CN1386140A - Cold rolled steel sheet and galvanized steel sheet having strain aging hardening property and method for producing the same - Google Patents

Abstract

An object of the present invention is to provide a cold-rolled steel sheet and an alloyed hot-dip galvanized steel sheet in which tensile strength is effectively increased by press forming and heat treatment while maintaining excellent deep drawability in press forming. Specifically, a steel composition contains less than 0.01% of C, 0.005 to 1.0% of Si, 0.01 to 1.0% of Mn, 0.005 to 0.050% of Nb, 0.005 to 0.030% of Al, 0.005 to 0.040% of N, 0.0005 to 0.0015% of B, 0.05% or less of P, and 0.01% or less of S, the balance substantially composed of Fe, in which the following equations (1) and (2) are satisfied: N% >=0.0015 + 14/93-Nb% + 14/27-Al% + 14/11-B% C% <= (12/93)-Nb%.

Description

Cold-rolled steel sheet, steel plate galvanized and manufacture method thereof with strain-aged hardening characteristics

Technical field

The present invention relates to be used for building slab, physical construction and implement intensity heat treated cold-rolled steel sheet sheet stock, that have excellent strain aging hardening properties, electrogalvanizing steel plate, hot-dip galvanized steel sheet and alloyed hot-dip galvanized steel plate and their manufacture method that is suitable as molding that rise with structural desired strengths such as parts, intensity when particularly being out of shape and/or inflexible position, adopting punching press etc. to shape the back with the structure of parts and automobile.

In addition, in the present invention, so-called " having excellent strain aging hardening properties " is meant: after the predeformation of tension strain 5%, with when 170 ℃ temperature, the condition that kept 20 minutes are carried out ageing treatment, the deformation stress increasing amount before and after this ageing treatment (is designated as the BH amount; Predeformation stress before yielding stress-ageing treatment after the BH amount=ageing treatment) be more than the 80MPa, and the tensile strength increasing amount before and after the strain aging processing (aforementioned predeformation+aforementioned ageing treatment) (is designated as Δ TS; Tensile strength before tensile strength-predeformation after the Δ TS=ageing treatment) be more than the 40MPa.

Background technology

When the manufacturing steel-sheet strikes out body, thereby, developed the BH steel plate as the steel plate of such baking usefulness of spraying paint as forming soft so that drawing before the drawing easily, the method for the baking of spraying paint is arranged under 200 ℃ of less thaies in the method that improves strength of parts of making it after the drawing to harden.

For example, the spy open clear 55-141526 communique disclose according to the C in the steel, N, Al content add Nb, the Nb/ (solid solution C+ solid solution N) that will represent with at% is when being limited in specified range, adjusts the solid solution C in the steel plate, the method for solid solution N by the speed of cooling after the control annealing; Special public clear 61-45689 communique discloses the method that baking hardenability is improved by compound interpolation Ti and Nb.

, above-mentioned steel plate is in order to form the good material of deep-draw ductility, and the intensity of sheet stock is low, may not be sufficient as the structure material material.

In addition, the spy opens flat 5-25549 communique and discloses the method that improves baking hardenability by single ground or compound interpolation W, Cr, Mo in steel.

In above-mentioned prior art, by baking hardening intensity being risen is the solid solution C that has utilized the trace in the steel plate, the effect of solid solution N, and in addition as is well known, the situation of BH steel plate is that YIELD STRENGTH is risen, and tensile strength is risen.So, have only the effect of the distortion initial stress that improves parts, improve from distortion and begin can not say so fully to the effect of the needed stress of distortion (tensile strength after the shaping) in the whole deformed zone territory that distortion is finished.

As the cold-rolled steel sheet that rises in shaping back draft intensity, for example specially open flat 10-310847 communique and disclose alloyed hot-dip galvanized steel plate more than tensile strength rising 60MPa under 200～450 ℃ the thermal treatment temp district.

This steel plate, its composition is represented with quality %, containing C:0.01～0.08%, Mn:0.01～3.0% and containing the total amount is 0.05～3.0% W, Cr, more than a kind or 2 kinds of Mo, contain Ti:0.005～0.1%, Nb:0.005～0.1%, more than a kind or 2 kinds of V:0.005～0.1% in addition as required, and the microtexture of steel is made of ferrite or ferrite main body.

; this technology forms fine carbide by the thermal treatment after being shaped in steel plate; dislocation is bred in the strain of giving when making punching press effectively; dependent variable is increased; therefore; need heat-treat 220～370 ℃ temperature range, the difficult point of existence is that needed thermal treatment temp is than general baking hardening treatment temp height.

And, being associated with the discharge gas regulation of the nearest global environment problem that is derived from, alleviating of the car body weight of automobile becomes epochmaking problem.In order to alleviate the car body weight of automobile, increase the intensity of employed steel plate, that is to say the use high tensile steel plate, the steel plate attenuation of use is effective.

Used the trolley part of the high tensile steel plate of minimal thickness, must bring into play fully with the characteristic that its effect adapts.Characteristic is according to the difference of parts and difference, and static strength corresponding to print resistance, bending, torsional deformation, resistance to fatigue, shock-resistant characteristic etc. are for example arranged.That is, the employed high tensile steel plate of trolley part need be all good in these characteristics of processing back that are shaped.These characteristics have relation with the intensity of the steel plate after processing that is shaped, so in order to reach minimal thicknessization, need to set the low intensity limit of the high tensile steel plate that uses.

On the other hand, in the process of making trolley part, steel plate is carried out drawing.Under the situation of drawing, when the intensity of steel plate was too high, the problem of generation was: 1. shape freezing deterioration; 2. ductility reduces, and cracks when being shaped and unfavorable condition such as necking down; 3. in addition, when reducing thickness of slab, print resistance (for the patience of the pit that is produced by partial compressive load load) deterioration has hindered the application of high tensile steel plate to car body thus.

As the method for breaking this situation, for example the cold-rolled steel sheet of using for outer plate panel is known that with ultralow carbon steel be starting material, will finally be controlled at the steel plate of proper range with the remaining C amount of solid solution attitude.This steel plate remains soft when drawing, guarantee shape freezing, ductility, the strain-age hardening phenomenon that the spray paint roasting procedure of utilization about 170 ℃ that carry out after the drawing * 20 minutes causes obtains the rising of yielding stress, guarantees print resistance.The C solid solution is in steel when drawing for this steel plate, and for soft, on the other hand, after drawing, in the dislocation that is imported when solid solution C is fixed in drawing in the roasting procedure that sprays paint, thereby yielding stress rises.

, for this steel plate, consider that from the viewpoint of the generation of the tension strain that prevents to become surface imperfection the yielding stress ascending amount that is produced by strain-age hardening is suppressed very lowly.Therefore, the difficult point of existence is in fact to help the light-weighted effect of parts little.

On the other hand, less become the purposes of problem for outward appearance, thereby proposed to use solid solution N further to increase the steel plate of baking hardening amount and be organized as the steel plate that the complex tissue that is made of ferrite and martensite further improves baking hardenability by making.

For example, the spy open clear 60-52528 communique disclose will contain that C:0.02～0.15%, Mn:0.8～3.5%, P:0.02～0.15%, Al:0.10% are following, the steel of N:0.005～0.025% the temperature below 550 ℃ reel make hot rolling and cold rolling after the manufacture method that is annealed into all good high-strength steel sheet of the heat treated ductility of controlled chilling and spot-welded on.Adopt the special steel plate of opening the technology manufacturing of clear 60-52528 communique record to have the mixed structure that constitutes mutually by low temperature phase change resultant based on ferrite and martensite, when ductility was good, the strain aging when utilization is toasted by spraying paint of the N generation of adding energetically obtained high strength.

; open the technology of clear 60-52528 communique record for the spy; the increasing amount of the yielding stress YS that is produced by strain-age hardening is big; but the increasing amount of tensile strength TS is few; in addition; the fluctuation of mechanical propertiess such as the increasing amount of yielding stress YS is also discrete widely is also big, and therefore the desired light-weighted steel plate of trolley part that helps can not expect to realize minimal thickness on present situation.

Again, special fair 5-24979 communique discloses to have and has contained C:0.08～0.20%, Mn:1.5～3.5%, remainder and be grouped into, organized by containing uniform bainite or a part of martensitic bainite baking hardenability high strength cold-rolled steel sheet that constitute of ferrite content below 5% by the one-tenth that Fe and unavoidable impurities constitute.The cold-rolled steel sheet of special fair 5-24979 communique record, in the process of cooling after continuous annealing, with 400～200 ℃ temperature range chilling, the slow cooling by thereafter makes the tissue that is organized as the bainite main body, the high baking hardening amount that was not in the past had.

; though the steel plate of special fair 5-24979 communique record rises in the baking back yield strength of spraying paint, the high baking hardening amount that was not in the past had, connecting tensile strength can not rise; when being used for strength member, the resistent fatigue characteristic after can not expecting to be shaped, the raising of shock-resistant characteristic.Therefore, the problem of leaving over is can not be applied on the purposes of strong request resistent fatigue characteristic, shock-resistant characteristic etc.

Again, special public clear 61-12008 communique discloses the manufacture method of the high tensile steel plate with high r value, this manufacture method has and is characterised in that: with ultralow C steel is starting material, in the annealing of ferritic-austenitic coexistence, the steel plate of gained has high r value and the high baking hardenability that sprays paint (BH) in cold rolling back, but the BH of gained amount is about 60MPa at most, in addition, though this steel plate yield-point after timeliness also rises, TS does not rise, and has limited this problem of parts applicatory.

And, for above-mentioned steel plate in the past, though in the intensity evaluation after the baking processing of spraying paint of being undertaken by simple tension test is good, but according to actual punching press condition, intensity during viscous deformation exists very big discrete, may not can be described as fully when being applied to require the parts of reliability.

In striking out the baking steel plate that sprays paint of body, about hot-rolled steel sheet, for example special fair 8-23048 communique disclose add man-hour be soft, handle and to improving the manufacture method that fatigue characteristic effectively make the hot-rolled steel sheet that tensile strength rises significantly by the baking vanish after the processing.

In this technology, making the C amount is 0.02～0.13 quality %, with the N volume be added to 0.0080～0.0250 quality %, control final rolling temperature and coiling temperature in addition, the solid solution N of volume is residued in the steel, making metal structure is complex tissue based on ferrite and martensite, thereby in shaping postheat treatment temperature: 170 ℃ of increases that are issued to the tensile strength more than the 100MPa.

In addition, when Te Kaiping 10-183301 communique discloses in the composition of steel particularly C and N has been limited in C:0.01～0.12 quality %, N:0.0001～0.01 quality %, the average crystal grain particle diameter is controlled at below the 8 μ m, the high BH amount that 80MPa is above be can guarantee in view of the above, baking hardenability and the good hot-rolled steel sheet of anti-room-temperature aging below the 45MPa simultaneously the AI amount are suppressed at.

,,, therefore be difficult to obtain high r value, be difficult to have sufficient deep-draw ductility so by the austenite/ferrite transformation after the finish rolling, randomization is organized in ferritic set because these steel plates are hot-rolled sheets.

And as starting materials, even carry out cold rolling and recrystallization annealing, the tensile strength that also may not necessarily obtain after the shaping-thermal treatment the same with hot-rolled steel sheet rises and the high BH more than the 80MPa with the hot-rolled steel sheet that adopts these technology to obtain.This be because: different microtexture when structure of steel becomes with hot rolling by cold rolling and recrystallization annealing causes big strain accumulation, thereby forms carbide, nitride or carbonitride easily that the state of solid solution C and solid solution N changes when cold rolling in addition.

The present invention develops according to above-mentioned actual state, its purpose is: keep good deep-draw ductility when being provided at drawing, simultaneously the cold-rolled steel sheet that has excellent strain aging hardening properties and alloyed hot-dip galvanized steel plate and their the favourable manufacture method that makes the tensile strength increase by drawing-thermal treatment.

Again, the present invention is in view of the problem points of above-mentioned conventional art, and purpose also is: good deep-draw ductility of having of TS * r value 〉=750MPa and good strain-aged hardening characteristics (cold-rolled steel sheet and hot-dip galvanized steel sheet (hot-dip galvanized steel sheet that also comprises alloying) and their favourable manufacture method that the deep-drawing of BH 〉=80MPa and Δ TS 〉=40MPa) is used are provided.

Further, the present invention also aims to: solve the problem of above-mentioned conventional art, the trolley part that is applicable to the plasticity that requires height is provided, when soft, have high plasticity and stable quality characteristic, be configured as the trolley part of complicated shape easily, there is not resilience, reverse, the shape defect of warpage etc., the generation of crackle etc., and adopt the thermal treatment trolley part be configured as behind the trolley part can obtain full intensity, can help the light-weighted of car body fully, have high r value more than 1.2 and good strain-aged hardening characteristics high strength cold rolled steel plate and industrial can be at an easy rate, and do not destroy the manufacture method that these steel plates are made on shape ground.

Summary of the invention

The inventor is in order to finish above-mentioned problem, will form and creates conditions and carry out all changes, makes steel plate and carried out a lot of material evaluation experimental.The result obtains following knowledge: the N that will in the past less actively be utilized in the field that requires high working property is as strengthening element, advantageously make full use of the big strain-age hardening phenomenon that the effect by this strengthening element manifests, can easily obtain the raising of plasticity in view of the above simultaneously and be shaped after high strength.

And then, the inventor finds: in order advantageously to make full use of the caused strain-age hardening phenomenon by N, need the strain-age hardening phenomenon that will cause by N and automobile spray paint baking condition or further energetically the heat-treat condition after the shaping advantageously combine, for this reason, make hot-rolled condition and cold rolling, cold rolled annealed condition suitable, it is effective that the microstructure of steel plate and solid solution N amount are controlled at certain scope.Also find in addition: in order stably to manifest the strain-age hardening phenomenon that is caused by N, it is important particularly controlling Al content according to N content aspect composition.

And then, the inventor finds: in order to obtain high r value, and reduction C content, under the two-phase region temperature of ferritic-austenitic, implement continuous annealing, control cooling thereafter, be formed on the tissue that contains the acicular ferrite phase of representing with area occupation ratio more than 5% in the ferritic phase, the combination with such microstructure and suitable solid solution N amount can obtain having high r value, press formability is good and the cold-rolled steel sheet that has excellent strain aging hardening properties.Also find in addition: also can not occur in the past problem in view of the above, can effectively utilize N fully as the room-temperature aging deterioration of problem.

Promptly, the inventor finds: N is used as strengthening element, according to N content Al content is controlled at suitable scope, make hot-rolled condition and cold rolling, cold rolled annealed condition suitable simultaneously, make microstructure and solid solution N optimizing, can obtain in view of the above comparing, have high r value, have the steel plate of good especially plasticity and the above-mentioned unexistent strain-aged hardening characteristics of steel plate in the past with C-Mn steel plate, the precipitation strength shaped steel plate of in the past solution strengthening type.

In addition, steel plate of the present invention, the strength ratio steel plate height in the past after the baking processing of spraying paint that obtains by simple tension test, and also the intensity when making it viscous deformation according to actual punching press condition is discrete little, can obtain stable strength of parts characteristic, applicable to the parts that require reliability.For example, apply the part that strain, thickness of slab reduce significantly, its hardening capacity is big than other parts, as if with this bearing load merit rating of (thickness of slab) * (intensity), then is the direction of homogenizing, is stable as the intensity of parts.

The inventor further concentrates on studies repeatedly in order to reach above-mentioned purpose, and the result obtains following knowledge:

1) for tensile strength is risen, is necessary to carry out tensile deformation to import new dislocation.By interacting, even make that it is necessary reaching that dislocation that upper yield stress imports by predeformation do not move yet by the dislocation that be shaped to import and clearance type element or precipitate.

2), be necessary the thermal treatment temp after being shaped is brought up to more than 200 ℃ in order to obtain above-mentioned interaction by carbide, nitride or the carbonitride that forms W, Cr, Mo, Ti, Nb, Al etc.Therefore, positive effective utilization of clearance type element effectively utilize the carbide of Fe or the thermal treatment temp of the nitride of Fe after making shaping to reduce on this point be favourable.

3) in the clearance type element, with solid solution C ratio,, should be engaged in even reach surrender even its interaction with the dislocation that imports by being shaped of thermal treatment temp that solid solution N reduces after being shaped is also big, the dislocation that predeformation imported also is difficult to migration.

4) as the place that exists of the solid solution N in the steel, intragranular and crystal boundary are arranged, but for the later intensity increasing amount of the thermal treatment after being shaped, big big of grain boundary area.Be that size of microcrystal is favourable for a short time.

5) consider from the viewpoint that enlarges grain boundary area that in the time of with Nb and the compound interpolation of B, cooling immediately can suppress normally the growing up of ferrite crystal grain after hot rolling is finished after finishing by hot rolling, and can be suppressed at the grain growth in the recrystallization annealing that follows closely after cold rolling.

The present invention finishes according to above-mentioned knowledge.Above-mentioned knowledge is obtained by following experiment.

Experiment 1

% represents with quality, to contain C:0.0015%, B:0.0010%, Si:0.01%, Mn:0.5%, P:0.03%, S:0.008% and N:0.011% and contain in 0.005～0.05% scope that Nb, scope 0.005～0.03% contain Al, remainder is the thin slab (thickness: 30mm) behind 1150 ℃ of even heating, be Ar in processing temperature of the composition of Fe and unavoidable impurities ₃Carry out hot rolling with 3 passes under 900 ℃ the prerequisite more than the transformation temperature, after rolling the finishing, water-cooled after 0.1 second.Implement then 500 ℃, 1 hour be equivalent to reel the thermal treatment of coiled material.

The hot-rolled sheet of thickness of slab with gained: 4mm is with draft: 82.5% cold rolling after, implement 800 ℃, the recrystallization annealing in 40 seconds, then implement draft: 0.8% skin-pass.Produce No. 5 tension test sheets of JIS from the cold-reduced sheet upper edge rolling direction that obtains like this, use common tensile testing machine, with rate of straining: measured tensile strength in 0.02/ second.Again, bestow in addition the tension strain of No. 5 tension test sheets of producing from these cold-reduced sheet upper edge rolling directions 10% of JIS, implement 120 ℃, 20 minutes thermal treatment after, be used for common tension test.With the difference of the tensile strength of these test films of producing from cold-reduced sheet and the tensile strength of bestowing the heat treated test film that has carried out 120 ℃, 20 minutes after 10% the tension strain as shaping back draft intensity ascending amount (Δ TS).

Fig. 1 represents the result that studies about the relation of composition of steel (N%-14/93Nb%-14/27Al%-14/11B%) and Δ TS.

Distinguish: according to shown in this figure like that, satisfy 0.0015 quality % when above in the value of (N%-14/93Nb%-14/27Al%-14/11B%), Δ TS reaches more than the 60MPa.

Experiment 2

% represents with quality, to contain C:0.0010%, Si:0.02%, Mn:0.6%, P:0.01%, S:0.009%, N:0.012%, Al:0.01% and Nb:0.015% and contain B in 0.00005～0.0025% scope, remainder is the thin slab (thickness: 30mm) behind 1100 ℃ of even heating, be Ar in processing temperature of the composition of Fe and unavoidable impurities ₃Carry out 3 groove rollings under above 920 ℃ the prerequisite of transformation temperature, after rolling the finishing, water-cooled after 0.1 second kind, implement 450 ℃, 1 hour be equivalent to reel the thermal treatment of coiled material.

The hot-rolled sheet of thickness of slab with gained: 4mm is with draft: 82.5% cold rolling after, implement the recrystallization annealing of 820 ℃, 40 seconds kinds, then implement draft: 0.8% skin-pass.

Produce JIS5 tension test sheet from the cold machine plate upper edge rolling direction of such acquisition, use common tensile testing machine, with rate of straining: measured tensile strength in 0.02/ second.Again, bestow in addition the tension strain of the tension test sheet of producing from these cold-reduced sheets 10%, implement 120 ℃, 20 minutes thermal treatment after, be used for common tension test.

Fig. 2 represents the result that studies about the relation of B content in the steel and Δ TS.As can be known, according to shown in this figure like that, when containing the B of 0.0005～0.0015 quality %, can obtain the above high Δ TS of 60MPa.

In addition, by compound interpolation Nb and B, crystal grain can be obtained high Δ TS by refinement, and this distinguishes by microstructure observation.

That is, can infer: when B quantity not sufficient 0.0005 quality %, the grain refining effect that produces by the compound interpolation with Nb is little.On the contrary, when B amount surpasses 0.0015 quality %, crystal boundary and near the B amount of segregation increase because this B atom is strong with the interatomic interaction of N, so effectively solid solution N amount reduces, so Δ TS reduction.

Experiment 3

% represents with quality, steel A consists of: contain C:0.0010%, N:0.012%, B:0.0010%, Si:0.01%, Mn:0.5%, P:0.03%, S:0.008%, Nb:0.014% and Al:0.01%, remainder is Fe and unavoidable impurities; Steel B consists of: contain C:0.010%, N:0.0012%, B:0.0010%, Si:0.01%, Mn:0.5%, P:0.03%, S:0.008%, Nb:0.014% and Al:0.01%, remainder is Fe and unavoidable impurities.Each thin slab (thickness: 30mm) behind 1150 ℃ of even heating, be Ar with steel A and steel B in processing temperature ₃Carry out 3 groove rollings under above 910 ℃ the prerequisite of transformation temperature, after rolling the finishing, began gas cooling after the kind at 0.1 second, then implement 600 ℃, 1 hour be equivalent to reel the thermal treatment of coiled material.

The hot-rolled sheet of thickness of slab with gained: 4mm is with draft: 82.5% cold rolling after, implement the recrystallization annealing of 880 ℃, 40 seconds kinds, then implement draft: 0.8% skin-pass.

Produce No. 5 tension test sheets of JIS from the cold-reduced sheet upper edge rolling direction that makes like this, use common tensile testing machine, with rate of straining: measured tensile strength in 0.02/ second.Again, bestow in addition the tension strain of the tension test sheet of producing from these cold-reduced sheets 10%, implement the thermal treatment of 20 fens kinds at various temperatures after, be used for common tension test.

The result that the influence of Δ TS was studied when Fig. 3 represented about the thermal treatment temp after being shaped.According to shown in this figure like that, in the thermal treatment temp after the shaping is lower zone below 200 ℃, demonstrate as Ultra-low carbon, the steel A that contains the steel of high N then that to liken to be the also high Δ TS of steel B of the low N steel of half Ultra-low carbon,, demonstrate the Δ TS of same degree in the high-temperature zone.From these experimental results as can be known, guarantee the Δ TS at cold zone, it is effective making full use of solid solution N.

In addition, Fig. 4 represents about size of microcrystal d and composition of steel (N%-14/93Nb%-14/27Al%-14/11B%) by the reduction amount (Δ E1) of the unit elongation due to the room temperature ageing with the result that studies of the influence of the tensile strength ascending amount (Δ TS) after being shaped.Moreover the breaking elongation that No. 5 test films of JIS that the reduction amount of unit elongation (Δ E1) is produced from cold-reduced sheet upper edge rolling direction with employing are measured is estimated with using the test film of producing in addition, the difference that execution is handled the breaking elongation of measuring the back as the maintenance at 100 ℃, 8 hours of the promotion processing of room temperature ageing.

As can be known, according to shown in this figure like that, value (N%-14/93Nb%-14/27Al%-14/11B%) is that the above and size of microcrystal d of 0.0015 quality % is 20 μ m when following, can obtain high Δ TS and low Δ E1 simultaneously.

Experiment 4

The thin slab of 0.0015%C-0.30%Si-0.8%Mn-0.03%P-0.005%S-0.012%N-0.02～0.08%Al steel is heated to 1050 ℃ equably, then under being 670 ℃ prerequisite, processing temperature carries out hot finishing with 7 passes, then carry out 700 ℃ * 5 hours recrystallization annealing, with the hot-rolled sheet of the thickness of slab 4mm that makes with draft: 82.5% is cold rolling, then to carry out recrystallization annealing in 875 ℃ * 40 seconds, then carry out skin-pass with draft 0.8%, produce No. 5 tension test sheets of JIS from the cold-reduced sheet of gained, use common tensile testing machine with rate of straining 3 * 10 ^-3Carry out tension test/second, measure TS * r value and Δ TS.The results are shown in table 5.Satisfying N/Al 〉=0.30 o'clock, can realize TS * r value 〉=750MPa and Δ TS 〉=40MPa.Moreover N/Al 〉=0.30 o'clock can realize that the situation of BH 〉=80MPa has confirmed separately.

Experiment 5

The thin slab of 0.0015%C-0.0010%B-0.01%Si-0.5%Mn-0.03%P-0.008%S-0.011%N-0.005～0.05%Nb-0.005～0.03%Al steel is heated to 1000 ℃ equably, then under being 650 ℃ prerequisite, processing temperature carries out hot finishing with 7 passes, carry out 800 ℃ * 60 seconds recrystallization annealing then, with the hot-rolled sheet of the thickness of slab 4mm that makes with draft: 82.5% is cold rolling, then under 880 ℃ * 40 seconds, carry out recrystallization annealing, carry out skin-pass with draft 0.8% then, produce No. 5 tension test sheets of JIS from the cold-reduced sheet of gained, use common tensile testing machine with rate of straining 3 * 10 ^-3Carry out tension test/second, measured TS * r value, BH, Δ TS.The relation of these measured values and N/ (Al+Nb+B) is shown in Fig. 5.In this experiment, use the steel that contains Nb:0.005～0.05%, B:0.0010%, as shown in Figure 5, in the scope of N/ (Al+Nb+B) 〉=0.30, can realize BH 〉=80MPa, Δ TS 〉=60MPa, TS * r value 〉=850MPa.

Experiment 6

The thin slab of 0.0010%C-0.02%Si-0.6%Mn-0.01%P-0.009%S-0.015%N-0.01%Al-0 .015%Nb-0.0001～0.0025%B steel is heated to 1050 ℃ equably, then under being 680 ℃ prerequisite, processing temperature carries out hot finishing with 7 passes, recrystallization annealing is carried out in the annealing of adopting then 750 ℃ * 5 hours at intermittence, carry out cold rolling with draft 82.5% hot-rolled sheet of the thickness of slab 4mm of gained, then under 880 ℃ * 40 seconds, carry out recrystallization annealing, carry out skin-pass with draft 0.8% then, produce No. 5 tension test sheets of JIS from the cold-reduced sheet that makes, use common tensile testing machine with rate of straining 3 * 10 ^-3Carry out tension test/second, measure TS * r value, BH, Δ TS.The relation of these measured values and B amount is shown in Fig. 6.

As shown in Figure 6, in the scope of B:0.0003～0.0015%, except BH 〉=80MPa, can also realize as Δ TS level than B＜0.0003% o'clock high Δ TS 〉=60MPa, TS * r value 〉=850MPa.In addition, can be seen by microstructure observation: in this B weight range, crystal grain is especially by refinement.

Result by experiment 5,6 distinguishes: the scope of regulation N/ (Al+Nb+B) 〉=0.30, and B 〉=0.0003%, also by compound interpolation Nb, thus grain refining, Δ TS, TS * r value level further is enhanced.When B＜0.0003%, the grain refining effect that produces by compound interpolation not with Nb.On the other hand, when B＞0.0015%, instead characteristic reduces.This can infer be since crystal boundary and near the B amount of segregation increase, by B atom and the interatomic strong interaction of N, make the cause that effective solid solution N amount reduces.In addition, also carried out same investigation about adding Ti, V with the situation that replaces Nb, and confirmed to obtain the effect the same with Nb.The present invention is based on that above knowledge finishes, and its purport is as follows:

The 1st the present invention is a kind of cold-rolled steel sheet that has excellent strain aging hardening properties, it is characterized by: % represents with quality, have contain that C:0.15% is following, Si:1.0% following, Mn:2.0% is following, P:0.1% is following, S:0.01% is following, Al:0.005～0.030%, N:0.0050～0.0400% and N/Al:0.30 N above, the solid solution attitude are more than 0.0010%, remainder is by forming that Fe and unavoidable impurities constitute.

For the 1st invention, in aforementioned component, preferred especially following scope.Promptly, a kind of cold-rolled steel sheet that has excellent strain aging hardening properties, it is characterized by: % represents with quality, has to contain C: less than 0.01%, Si:0.005～1.0%, Mn:0.01～1.5%, P:0.1% are following, S:0.01% is following, Al:0.005～0.030%, N:0.005～0.040% and N/Al:0.30 N above, the solid solution attitude are more than 0.0010%, remainder is by forming that Fe and unavoidable impurities constitute.

For the 1st invention, on the basis of above-mentioned composition, also contain B:0.0001～0.0030% represented with quality %, Nb:0.005～0.050% for well in the scope that satisfies following formula (1), (2).

N％≥0.0015+14/93·Nb％+14/27·Al％+14/11·B％??---(1)

C％≤0.5·(12/93)·Nb％????????????????????????????---(2)

For the 1st invention, on above-mentioned composition basis, also contain the total amount of representing with quality % as required and be Cu, Ni below 1.0%, the composition more than a kind or 2 kinds among the Mo for well.

For the 1st invention, the size of microcrystal of steel plate is that 20 μ m are following for well.

For the 1st invention, in thermal treatment temp: 120～200 ℃ cold zone has the intensity ascending amount after the shaping: more than the 60MPa.

For the 1st the present invention, also can possess electro-galvanizing, galvanizing and alloyed hot-dip zinc-coated layer on the surface of above-mentioned cold-rolled steel sheet.

The 2nd the present invention is a kind of manufacture method of the cold-rolled steel sheet that has excellent strain aging hardening properties, it is characterized in that: % represents with quality, to contain C: less than 0.01%, Si:0.005～1.0%, Mn:0.01～1.5%, below the P:0.1%, below the S:0.01%, Al:0.005～0.030%, N:0.005～0.040%, and content range satisfies more than the N/Al:0.30, the steel billet that remainder is essentially the composition of Fe carries out hot rolling, at this moment, after finishing, finish rolling begins to cool down immediately, in the coiling temperature: reel down for 400～800 ℃, implement draft then: 60～95% cold rolling after, under 650～900 ℃ temperature, implement recrystallization annealing.

For the 2nd the present invention, on the basis of above-mentioned composition, also contain B:0.0001～0.0030% represented with quality %, Nb:0.005～0.050% for well in the scope that satisfies following formula (1), (2).

N％≥0.0015+14/93·Nb％+14/27·Al％+14/11·B％??---(1)

C％≤0.5·(12/93)·Nb％????????????????????????????---(2)

For the 2nd the present invention, in the temperature-rise period of above-mentioned recrystallization annealing, heated up to well with 1～20 ℃/second speed in the humidity province of 500 ℃～recrystallization temperature.

For the 2nd the present invention, after recrystallization annealing, also can implement galvanizing and handle, then implement the heating Alloying Treatment.

The 3rd the present invention is a kind of deep-drawing that has excellent strain aging hardening properties cold-rolled steel sheet, it is characterized by: % represents with quality, have contain that C:0.01% is following, Si:1.0% following, Mn:0.01～1.5%, P:0.1% is following, S:0.01% is following, Al:0.005～0.020%, N:0.0050～0.040% and N/Al:0.30 N above, the solid solution attitude are more than 0.0010%, remainder is by forming that Fe and unavoidable impurities constitute, its TS * r value: more than the 750MPa.

For the 3rd the present invention, on the basis of above-mentioned composition, also contain B:0.0001～0.0030% represented with quality %, Nb:0.005～0.050% for well in the scope that satisfies following formula (1), (2).

N％≥0.0015+14/93·Nb％+14/27·Al％+14/11·B％??---(1)

C％≤0.5·(12/93)·Nb％????????????????????????????---(2)

For the 3rd the present invention, on the basis of above-mentioned composition, also contain the composition more than a kind or 2 kinds among B:0.0001～0.0030% represented with quality %, Nb:0.005～0.050%, Ti:0.005～0.070%, V:0.005～0.10%, and N/ (Al+Nb+Ti+V+B): more than 0.30, solid solution N:0.0010% is above for well.

The 4th the present invention is the manufacture method of a kind of deep-drawing that has excellent strain aging hardening properties with cold-rolled steel sheet, it is characterized in that: % represents with quality, to have below the C:0.01% of containing, Si:0.005～1.0%, Mn:0.01～1.0%, below the P:0.1%, below the S:0.01%, Al:0.005～0.030%, N:0.005～0.040%, contain B:0.0003～0.0030%, Nb:0.005～0.050%, Ti:0.005～0.070%, composition more than a kind or 2 kinds among V:0.005～0.10%, and N/ (Al+Nb+Ti+V+B): after the steel billet material of the composition more than 0.30 was heated to more than 950 ℃, making roughing finish temperature was below 1000 ℃, Ar ₃More than, carry out roughing, then at Ar ₃Below, the humidity province more than 600 ℃ is while lubricating finish rolling, coiling, make that to begin to total draft that finish rolling is finished from roughing be more than 80% this moment, the hot-rolled sheet of gained is carried out recrystallization annealing, then carry out cold rollingly, the cold-reduced sheet of gained is carried out recrystallization annealing with draft 60～95%.

The 5th the present invention is a kind of plasticity, strain-aged hardening characteristics and the good high strength cold rolled steel plate of anti-room temperature ageing, it is characterized in that: % represents with quality, has the C:0.0015 of containing～0.025%, below the Si:1.0%, below the Mn:2.0%, below the P:0.1%, below the S:0.02%, below the Al:0.02%, N:0.005 0～0.0250%, and contain B:0.0005～0.0050%, the composition more than a kind or 2 kinds of Nb:0.002～0.050%, and making N/Al is more than 0.3, the N of solid solution attitude is more than 0.0010%, remainder is by forming of constituting of Fe and unavoidable impurities and by the acicular ferrite of representing with area occupation ratio more than 5% mutually and median size: the tissue that the following ferritic phase of 20 μ m constitutes, its r value: more than 1.2.

For the 5th the present invention, on the basis of aforementioned component, also contain the composition more than 1 group or 2 groups among the following a group～c group of representing with quality % for well, wherein,

A group: among Cu, Ni, Cr, the Mo more than a kind or 2 kinds, the total amount is below 1.0%;

B group: among Ti, the V a kind or 2 kinds, the total amount is below 0.1%;

C group: Ca, REM a kind or 2 kinds, the total amount is 0.0010～0.010%.

The 6th the present invention is a kind of r value that has: more than 1.2, plasticity, the manufacture method of the high strength cold rolled steel plate that strain-aged hardening characteristics and anti-room temperature ageing are good, it is characterized in that: % represents with quality, to contain C:0.0015～0.025%, below the Si:1.0%, below the Mn:2.0%, below the P:0.1%, below the S:0.02%, below the Al:0.02%, N:0.0050～0.0250%, and contain B:0.0003～0.0050%, more than a kind or 2 kinds of Nb:0.002～0.050%, and N/Al is that the plate slab of the composition more than 0.3 is heated to slab heating temperature: more than 1000 ℃, carry out roughing and form thin slab, implement successively this thin slab execution finish rolling is gone out the material temperature: the finish rolling more than 800 ℃, and in the coiling temperature: form the hot-rolled process of hot-rolled sheet thereby reel below 650 ℃, thereby this hot-rolled sheet is implemented the cold rolling process of pickling and cold rolling formation cold-reduced sheet, under the temperature in ferrite-austenite two-phase region this cold-reduced sheet is carried out continuous annealing, with speed of cooling: 10～300 ℃ of/second cold-reduced sheet annealing operations that are cooled to the humidity province below 500 ℃.

For the 6th the present invention, on the basis of aforementioned component, also contain the composition more than 1 group or 2 groups among the following a group～c group of representing with quality % for well, wherein,

A group: among Cu, Ni, Cr, the Mo more than a kind or 2 kinds, the total amount is below 1.0%;

B group: among Ti, the V more than a kind or 2 kinds, the total amount is below 0.1%;

C group: Ca, REM a kind or 2 kinds, the total amount is 0.0010～0.010%.

The 7th the present invention is a kind of have high r value and good strain-aged hardening characteristics and non-ageing high strength cold rolled steel plate of normal temperature, it is characterized in that: % represents with quality, has the C:0.025 of containing～0.15%, below the Si:1.0%, below the Mn:2.0%, below the P:0.08%, below the S:0.02%, below the Al:0.02%, N:0.0050～0.0250%, and N/Al is more than 0.3, the N that contains the solid solution attitude more than 0.0010%, remainder is by forming that Fe and unavoidable impurities constitute, with contain the average crystal grain particle diameter of representing with area occupation ratio more than 80%: the ferritic phase that 10 μ m are following, also contain tissue, its r value: more than 1.2 as the martensitic phase of representing with area occupation ratio more than 2% of the 2nd phase.

For the 7th the present invention, on the basis of aforementioned component, also contain the composition more than 1 group or 2 groups among the following d group～g group of representing with quality % for well, wherein,

D group: among Cu, Ni, Cr, the Mo more than a kind or 2 kinds, the total amount is below 1.0%;

E group: among Nb, Ti, the V more than a kind or 2 kinds, the total amount is below 0.1%;

F group: the B below 0.0030%;

G group: among Ca, the REM a kind or 2 kinds, the total amount is 0.0010～0.010%.

The 8th the present invention has a r value for a kind of: the manufacture method of the non-ageing high strength cold rolled steel plate of high r value more than 1.2 and good strain-aged hardening characteristics and normal temperature, it is characterized in that: % represents with quality, to contain C:0.025～0.15%, below the Si:1.0%, below the Mn:2.0%, below the P:0.08%, below the S:0.02%, below the Al:0.02%, N:0.0050～0.0250%, and N/Al is that the plate slab of the composition more than 0.3 is heated to slab heating temperature: more than 1000 ℃, carry out roughing and form thin slab, implement successively this thin slab execution finish rolling is gone out the material temperature: the finish rolling more than 800 ℃, and in the coiling temperature: form the hot-rolled process of hot-rolled sheet thereby reel below 650 ℃, thereby this hot-rolled sheet is implemented the cold rolling process of pickling and cold rolling formation cold-reduced sheet, to this cold-reduced sheet in annealing temperature: more than the recrystallization temperature～implement pack annealing below 800 ℃, then at annealing temperature: Ac ₁Transformation temperature～(Ac ₃Transformation temperature-20 ℃) carries out continuous annealing under, then with speed of cooling: 10～300 ℃ of/second cold-reduced sheet annealing operations that are cooled to the humidity province below 500 ℃.

For the 8th the present invention, continue with cooling after the aforementioned continuous annealing, stop humidity province below the temperature, more than 350 ℃ in aforementioned refrigerative cooling and carry out the overaging of residence time more than 20 seconds and be treated to.

For the 8th the present invention, on the basis of aforementioned component, also contain the composition more than 1 group or 2 groups among the following d group～g group of representing with quality % for well, wherein,

D group: among Cu, Ni, Cr, the Mo more than a kind or 2 kinds, the total amount is below 1.0%;

E group: among Nb, Ti, the V more than a kind or 2 kinds, the total amount is below 0.1%;

F group: the B below 0.0030%;

G group: Ca, REM a kind or 2 kinds, the total amount is 0.0010～0.010%.

The simple declaration of accompanying drawing

Fig. 1 is the graphic representation of the relation of the tensile strength ascending amount (Δ TS) after expression composition of steel (N%-14/93Nb%-14/27Al%-14/11B%) and the shaping.

Fig. 2 is the figure that is illustrated in the relation of B content and Δ TS in the steel of compound interpolation Nb, B.

Fig. 3 is for solid solution C many steel B (steel always) and the many steel A (invention steel) of solid solution N, compares, shows the different graphic representation of the tensile strength ascending amount that is caused by the shaping postheat treatment at cold zone.

Fig. 4 is expression size of microcrystal d and composition of steel (N%-14/93Nb%-14/27Al%-14/11B%) to the figure of the influence of the reduction amount (Δ E1) of the unit elongation that is caused by room temperature ageing and shaping back draft intensity ascending amount (Δ TS).

Fig. 5 is the graphic representation of the relation of expression TS * r value, BH, Δ TS and N/ (Al+Nb+B).

Fig. 6 is the graphic representation of the relation of expression TS * r value, BH, Δ TS and B amount.

The preferred plan that carries out an invention

For the 1st the present invention, be grouped into the reason that is limited to aforementioned range about one-tenth and illustrated steel plate.

C: less than 0.01 quality %

As far as possible for a small amount of, deep-draw ductility is good more, is favourable aspect press formability for C.Again, in the annealing process after cold rolling, NbC dissolves again, and intragranular solid solution C increases, and causes anti-room temperature ageing reduction easily.Therefore, C amount is suppressed at less than 0.01 quality % for well.More preferably below the 0.0050 quality %, below the preferred especially 0.0030 quality %.

Si:0.005～1.0 quality %

Si is the useful component that suppresses the reduction of unit elongation, simultaneously intensity is improved, but its additive effect deficiency when containing quantity not sufficient 0.005 quality %, on the other hand, if surpass 1.0 quality %, surface texture is worsened, cause ductility to reduce, so Si is limited to the scope of 0.005～1.0 quality %.The more preferably scope of 0.01～0.75 quality %.

Mn:0.01～1.5 quality %

Mn is not only as the reinforcement composition of steel and useful, and formation MnS, the effect of the embrittlement that inhibition causes by S is arranged, but when containing quantity not sufficient 0.01 quality %, its additive effect deficiency, on the other hand, when surpassing 1.5 quality %, cause the deterioration and the ductility of surface texture to reduce, so regulation Mn contain in the scope of 0.01～1.5 quality %.More preferably 0.10～0.75 quality %.

Below the P:0.10 quality %

P helps the reinforcement of steel effectively as the solution strengthening composition, but addition form phosphides such as (FeNb) xP, so deep-draw ductility reduces when surpassing 0.10 quality %.Therefore P is limited to below the 0.10 quality %.

Below the S:0.01 quality %

When S is contained sometimes in a large number, the inclusion amount increases, and causes that ductility reduces, and therefore wish to do one's utmost to avoid sneaking into of S, but tolerable is to 0.01 quality %.

Al:0.005～0.030 quality %

Al is as reductor, simultaneously form effective utilization of composition and add in order to improve carbonitride, when containing quantity not sufficient 0.005 quality %, there is not effect of sufficient, on the other hand, when addition surpassed 0.030 quality %, the N amount that causes adding among the Ying Xianggang increased, and is easy to generate slab defect during steel-making.Therefore, regulation Al contains in the scope of 0.005～0.030 quality %.

N:0.005～0.040 quality %

N is the important element that plays the effect that gives the steel plate strain-aged hardening characteristics in the present invention., when containing quantity not sufficient 0.005 quality %, can not get sufficient strain-aged hardening characteristics, on the other hand, when volume increases above 0.040 quality %, cause the reduction of press formability.Therefore, regulation N contains in the scope of 0.005～0.040 quality %.Moreover, preferred 0.008～0.015 quality %.

B:0.0001～0.003 quality %

B by with the compound interpolation of Nb, refinement hot rolling microstructure and cold rolling recrystallized structure are improved the effect of anti-secondary processing brittleness in addition effectively., content is if less than 0.0001 quality % then can not get sufficient thinning effect, and on the other hand, when content surpassed 0.003 quality %, not only the BN amount of separating out increased, and was brought obstacle in the meltization of slab heating phase.Therefore B contains in the scope of 0.0001～0.003 quality %.Moreover, preferred 0.0001～0.0015 quality %, more preferably 0.0007～0.0012 quality %.

Nb:0.005～0.050 quality %

Nb by with the compound interpolation of B, help the refinement of hot rolling microstructure and cold rolling recrystallization annealing tissue effectively, have in addition with the fixedly effect of solid solution C of NbC form.Again, Nb forms this mononitride of NbN, helps the refinement of cold rolling recrystallization annealing tissue., when Nb less than 0.005 quality %, not only be difficult to solid solution C is separated out fixing, and the refinement of hot rolling microstructure and cold rolling recrystallization annealing tissue becomes insufficient, on the other hand, when surpassing 0.050 quality %, causes ductility to reduce.Therefore Nb contains in the scope of 0.005～0.050 quality %.Preferred 0.010～0.030 quality %.

In addition, according to above-mentioned, Nb has with the fixedly effect of solid solution C of NbC form.Form this mononitride of NbN again.Similarly, Al and B form AlN, BN respectively.Therefore, in order to guarantee solid solution N amount fully, reduce solid solution C fully simultaneously, the relation that satisfies following formula (1), (2) is important.

N％≥0.0015+14/93·Nb％+14/27·Al％+14/11·B％??---(1)

C％≤0.5·(12/93)·Nb％????????????????????????????---(2)

In addition, in this invention,, prevent the timeliness deterioration simultaneously, reduce size of microcrystal and be fit in order to obtain high distortion aging property.

That is, as shown in Figure 4, be reduced to below the 20 μ m by making size of microcrystal, at (N%-14/9 3Nb%-14/27Al%-14/11B%) 〉=0.0015 quality % with contain the occasion of the solid solution N of more amount, Δ E1 is suppressed to also becomes possibility below 2.0%.Moreover better situation is that size of microcrystal d is reduced to below the 15 μ m.This is because as shown in Figure 4, when size of microcrystal d being reduced to 15 μ m when following, Δ E1 is suppressed to becomes possibility below 1.5%.

Narrated about the 2nd of the present invention creating conditions.

Known smelting processes such as employing converter are smelted the steel that above-mentioned suitable component is formed, and adopt ingot casting method or continuous metal cast process to make steel billet.

Then, after this steel billet heating, soaking, implement hot rolling and make hot-rolled sheet.In this invention, the hot rolled Heating temperature is regulation especially, but in order to improve deep-draw ductility, it is favourable that solid solution C is fixedly made it to separate out with the carbide form, and for this reason, the hot rolled Heating temperature is for well below 1300 ℃.In addition, in order further to improve processibility, be taken as below 1150 ℃ to well., during 900 ℃ of Heating temperature less thaies, the improvement of processibility is saturated, and on the contrary, the rolling load during hot rolling increases, and the danger that rolling accident takes place increases, so the lower limit of Heating temperature is taken as 900 ℃ for well.

Secondly, the total draft during hot rolling is for well more than 70%.At this moment because: during total draft less than 70%, the grain refining of hot-rolled sheet becomes insufficient.

In addition, the finish rolling in the hot rolling is finished 960～650 ℃ humidity province to good, and the hot rolling processing temperature can be Ar ₃The γ district that transformation temperature is above also can be Ar ₃The α district that transformation temperature is following.When the hot rolling processing temperature surpasses 960 ℃, the grain coarsening of hot-rolled sheet, the deep-draw deteriorated ductility after cold rolled annealed.On the other hand, as if 650 ℃ of less thaies, then resistance to deformation increases, thus cause the hot rolling load to increase, the rolling difficulty that becomes.

After above-mentioned hot finishing is finished, begin to cool down immediately, wish that in view of the above when preventing normal grain growth, the AlN that also is suppressed in the process of cooling separates out.

At this, limit especially about above-mentioned cooling process condition, but wish the cooling time opening be after finish rolling is finished preferred 1.5 seconds with interior, more preferably 1.0 seconds with interior, most preferably in 0.5 second.This be because: when cooling off immediately after rolling the finishing, condensate depression becomes big under strain accumulative state, thus more ferrite nucleus generation, when promoting ferrite transformation, suppress the solid solution N of γ in mutually and be diffused in the ferrite crystal grain, the solid solution N amount that exists on the ferrite crystal boundary increases.

In addition, about speed of cooling,, be taken as more than 10 ℃/second to well in order to ensure solid solution N.Moreover, be Ar particularly in the hot rolling processing temperature ₃The occasion that transformation temperature is above is taken as 50 ℃/second with speed of cooling and is more suitable for aspect the solid solution N guaranteeing.

Secondly, with hot-rolled sheet coil coiled coiled material.This coiling temperature is high temperature, help the alligatoring of carbide more, but when surpassing 800 ℃, at the formed scale thing thickening in hot-rolled sheet surface, the load of not only removing the operation of scale thing increases, and carry out nitride and form, cause the coiled material fluctuation of solid solution N amount longitudinally, on the other hand, as if 400 ℃ of coiling temperature less thaies, then winding work becomes difficult, so the coiling temperature of hot-rolled sheet must be taken as 800～400 ℃ scope.

Secondly, hot-rolled sheet is implemented cold rolling, but must be taken as 60～95% at this draft in cold rolling.This be because: when cold rolling draft less than 60%, can not expect high r value, on the other hand, when above 95% the time, instead the r value reduces.

Implement above-mentioned cold rolling cold-reduced sheet and be then used in recrystallization annealing.Method for annealing can be continuous annealing, also can be intermittently annealing, wherein any can, but continuous annealing is favourable.Moreover this continuous annealing can be at any of processing on the common continuous annealing line or the processing on the continuous hot-dipping zinc wire.

In addition, annealing conditions be taken as more than 650 ℃, more than 5 seconds for well.This be because: 650 ℃ of annealing temperature less thaies, annealing conditions less than can not be finished recrystallize in the time of 5 seconds, so deep-draw ductility reduces.In order to improve deep-draw ductility more, wish in the annealing of the ferrite single phase region more than 800 ℃ more than 5 seconds.

In addition, by in the more annealing of pyritous α+γ two-phase region, α → γ phase transformation takes place partly, { 111} set tissue is flourishing, and r value improves, but α → γ phase transformation is when fully carrying out, and randomization is organized in set, so the reduction of r value, and deep-draw ductility is compromised thus.

Moreover the upper limit of annealing temperature is taken as 900 ℃ for well.This be because, when annealing temperature surpassed 900 ℃, the dissolving again of carbide was carried out, solid solution C excessively increases, slow ageing reduction, in addition, in the occasion that α → γ phase transformation takes place, randomization is organized in set, so the reduction of r value, deep-draw ductility is compromised.

Again, in the temperature-rise period of above-mentioned recrystallization annealing, make from 500 ℃ of humidity provinces and slowly heat, AlN etc. is separated out fully, can reduce the size of microcrystal of steel plate in view of the above effectively to recrystallization temperature.

Here, the humidity province that should implement above-mentioned control heating for begin to separate out from AlN etc. 500 ℃ to recrystallization temperature.

In addition, heat-up rate is taken as 1～20 ℃/second for well.This be because: when heat-up rate surpasses 20 ℃/second, the amount separated out fully, on the other hand, during 1 ℃/second of less than, the precipitate alligatoring is a little less than the inhibition effect of grain growth.

Moreover, after above-mentioned recrystallization annealing,, also can carry out the skin-pass below 10% in order to carry out shape correction, surface smoothness adjustment further.

In addition, the speed of cooling after the soaking in the recrystallization annealing is taken as 10～50 ℃/second for well.This be because, during 10 ℃/second of speed of cooling less thaies, cause grain growth in the cooling, cause grain coarsening, distortion aging property and aging characteristic at normal temperatures reduce.On the other hand, more than 50 ℃/second the time, the N of solid solution attitude can not take place fully to the diffusion of crystal boundary, and aging characteristic is at normal temperatures reduced.Moreover, preferred 10～30 ℃/second.

Continue with above-mentioned recrystallization annealing, carry out galvanizing as required and handle, then heat Alloying Treatment, form alloyed hot-dip galvanized steel plate in view of the above.

Handle and Alloying Treatment about such galvanizing, limit especially, as long as according to known method always.

Moreover, form after the alloyed hot-dip galvanized steel plate, the surface-treated steel plate that had execution that the steel plate etc. of slushing oil, lubricated wet goods oil lamella adopts as steel sheet usually for the steel plate of implementing skin-pass for the outward appearance after improving processibility and improving processing (passivity is handled the steel plate that steel plate, light processing steel plate, surface form specific roughness decorative pattern), surface, if in this invention scope, then can obtain the effect of this invention fully.

Like this, can not only be had good deep-draw ductility, and be made the cold-rolled steel sheet that has excellent strain aging hardening properties and the alloyed hot-dip galvanized steel plate of tensile strength increase by drawing-thermal treatment.

Illustrated about in the 3rd the present invention, the one-tenth of steel plate being grouped into the reason that is limited to aforementioned range.

C: less than 0.01 quality %

C is a small amount of as far as possible, and deep-draw ductility is good more, and is favourable aspect press formability.In addition, in the annealing process after cold rolling, carry out the dissolving again of NbC, intragranular solid solution C increases, and causes the reduction of anti-room temperature ageing easily.Therefore, C amount is suppressed at less than 0.01 quality % for well.More preferably below the 0.0050 quality %, most preferably below the 0.0030 quality %.Moreover, from guaranteeing intensity and the viewpoint that prevents grain coarsening, wish that C contains more than 0.0005%.Si:0.005～1.0 quality %

Si suppresses the useful component that unit elongation reduces and improve intensity, but when containing quantity not sufficient 0.005 quality %, its additive effect deficiency, on the other hand, when surpassing 1.0 quality %, surface texture is worsened, cause ductility to reduce, so Si is limited to the scope of 0.005～1.0 quality %.The scope of 0.01～0.75 quality % more preferably.Mn:0.01～1.5 quality %

Mn is not only as the reinforcement composition of steel and useful, and formation MnS, the effect of the embrittlement that inhibition causes by S is arranged, but when containing quantity not sufficient 0.01 quality %, its additive effect deficiency, on the other hand, when surpassing 1.5 quality %, cause surface texture to worsen and the ductility reduction, so Mn contains in the scope of 0.01～1.5 quality %.More preferably 0.10～0.75 quality %.Below the P:0.10 quality %

P helps the reinforcement of steel effectively as the solution strengthening composition, but addition form phosphides such as (FeNb) xP, thereby deep-draw ductility reduces when surpassing 0.10 quality %.Therefore, P is limited to below the 0.10 quality %.Below the S:0.01 quality %

The S volume contains sometimes, and the inclusion amount increases, and causes ductility to reduce, and therefore wishes to do one's utmost to avoid sneaking into of S, but can allow 0.01 quality %.Al:0.005～0.030 quality %

Al is as reductor, also form effective utilization of composition and add in order to improve carbonitride, but if content is less than 0.005 quality %, then there is not effect of sufficient, on the other hand, when addition surpassed 0.030 quality %, the N amount that causes adding among the Ying Xianggang increased the slab defect when easily steel-making taking place.Therefore, Al contains in the scope of 0.005～0.030 quality %.N:0.005～0.040 quality %

N has been the important element that gives the effect of steel plate strain-aged hardening characteristics in the present invention.,, then sufficient strain-aged hardening characteristics can not be obtained, on the other hand, when volume is added above 0.04 quality %, the reduction of press formability will be caused if contain quantity not sufficient 0.005 quality %.Therefore, N contains in the scope of 0.005～0.040 quality %.Moreover, preferred 0.008～0.015 quality %.B:0.0001～0.003 quality %

B by with the compound interpolation of Nb, refinement hot rolling microstructure and cold rolling recrystallized structure are improved the effect of anti-secondary processing brittleness in addition effectively., if contain quantity not sufficient 0.0001 quality %, then can not get sufficient thinning effect, on the other hand, when surpassing 0.003 quality %, not only the BN amount of separating out increases, and brings obstacle for the solutionizing of slab in the heating phase.Therefore, B contains in the scope of 0.0001～0.003 quality %.Moreover, preferred 0.0001～0.0015 quality %, more preferably 0.0007～0.0012 quality %.Nb：0.005～0.050％、Ti：0.005～0.070％、V：0.005～0.10％

Nb, Ti, V by with the compound interpolation of B, help refinement hot rolling microstructure and cold rolling recrystallized structure, and have the effect that C is separated out with NbC, TiC, VC form, therefore add with B as required, but during difference less than 0.005 quality, its effect is insufficient.On the other hand, when Nb surpasses 0.05%, Ti surpasses 0.070%, when V surpasses 0.10%, causes deteriorated ductility.So Nb is taken as 0.005～0.050%, Ti is taken as 0.005～0.070%, V is taken as 0.005～0.10%.

In addition, according to above-mentioned, Nb has with the fixedly effect of solid solution C of NbC form.Also form this mononitride of NbN.Similarly, Al and B form AlN, BN respectively.Therefore, in order fully to guarantee solid solution N amount, reduce solid solution C fully simultaneously, the relation that satisfies following formula (1), (2) is important.

N％≥0.0015+14/93·Nb％+14/27·Al％+14/11·B％??---(1)

C%≤0.5 (12/93) Nb%---(2) N/Al or N/ (Al+Nb+Ti+V+B): more than 0.30

Al forms AlN and reduces solid solution N.In order to ensure the appropriate amount of solid solution N, must make N/Al is more than 0.30.In addition, when compound interpolation Nb, Ti, V or B, they all form NbN, TiN respectively, VN, BN reduce solid solution N, so in order to ensure the appropriate amount of solid solution N, must make N/ (Al+Nb+Ti+V+B) is more than 0.30.More than the solid solution N:0.0010%

In order to improve the strain-aged hardening characteristics of steel plate, solid solution N must exist with the content more than 0.0010%.

At this, the solid solution N amount total N content from steel deducts separates out the N amount and tries to achieve.Moreover as separating out N quantitative analysis method, the inventor compares, has studied various analytical methods, and according to the result, it is effective adopting the electrolytic extraction analytical method of having used the constant potential electrolytic process to try to achieve.Moreover, be used to extract the method for the iron matrix of analysis as dissolving, acid decomposition, halogen method and electrolytic process are arranged.Wherein, electrolytic process can not make extremely unsettled precipitate such as carbide, nitride decompose, and can only stably dissolve iron matrix.Use methyl ethyl diketone system, electrolysis under constant potential as electrolytic solution.In the present invention, use the constant potential electrolytic process to measure to separate out the result of N amount to demonstrate and best corresponding of the strength of parts of reality.

Thus, in the present invention, will utilize the residue of constant potential electrolytic process extraction to carry out chemical analysis, obtain the N amount in the residue, it will be measured as separating out N.

Moreover, in order to obtain higher BH and Δ TS, solid solution N amount more than 0.0015% for well, more preferably more than 0.0020%, preferred especially more than 0.0030%.

Cold-rolled steel sheet of the present invention be with have above-mentioned composition, simultaneously TS * r value 〉=750MPa is the deep-drawing cold-rolled steel sheet that has excellent strain aging hardening properties of feature.

For the steel plate of TS * r value, can not be widely used in having the member of the key element of structural member less than 750MPa.In addition, in order further to enlarge the scope of application, TS * r value is for well more than the 850MPa.

The baking processing condition of spraying paint in the past adopts 170 ℃ * 20 minutes as standard.Moreover, the steel plate of the present invention of the solid solution N that contains volume is applied strained occasion more than 5%, even more demulcent (low temperature one side) processing also can realize sclerosis, in other words, acquisitive prescription condition more in a wide range.In addition, in general, in order to strive for hardening capacity, only otherwise soften because of the over-drastic timeliness, then maintenance is favourable for more time under high temperature more.

Narration particularly, for steel plate of the present invention, the become lower limit of significant Heating temperature of predeformation post-hardening is about 100 ℃.On the other hand, when Heating temperature surpassed 300 ℃, sclerosis culminated, and has occurred remollescent trend a little on the contrary, and thermal strain and tempering color becomes remarkable in addition.In addition, about the hold-time, when 200 ℃ of left and right sides of Heating temperature, if more than being about about 30 seconds, then can reach sufficient sclerosis substantially.In order further to obtain big stable sclerosis, the hold-time is for well more than 60 seconds.,, then not only can not wish further to be hardened if the hold-time surpasses 20 minutes, however production efficiency reduce significantly, unfavorable aspect practical.

Because above situation, in the present invention, be decided to be: to estimate 170 ℃, the hold-time in 20 minutes as the Heating temperature of in the past the baking processing condition of spraying paint as the ageing treatment condition.Even the baking-type steel plate that sprays paint in the past can not reach under the ageing treatment condition of sufficient hardened low-temperature heat short period of time maintenance, steel plate of the present invention also can stably reach sufficient sclerosis.Moreover the method for heating does not limit especially, removes atmosphere that the stove that utilizes the common baking of spraying paint to be adopted carries out heats, and for example utilizes heating that induction heating, non-oxidation flame, laser, plasma etc. carry out etc. to use well.In addition, also can only optionally heat the part that intensity is risen.

Automobile must be able to be resisted stress-loaded from the complexity of outside with strength of parts, so for sheet stock, not only the strength characteristics at little strain regions is important, and also is important in the strength characteristics of big strain regions.The inventor is according to this point, and making the BH that will make the raw-material steel plate of the present invention of trolley part is more than the 80MPa, and making Δ TS simultaneously is more than the 40MPa.Moreover more preferably BH is that 100MPa is above, Δ TS is more than the 50MPa.In order to make BH and Δ TS bigger, as long as the Heating temperature during with ageing treatment is set in more high temperature one side and/or will be set in longer time one side the hold-time.

In addition, steel plate of the present invention possesses the following advantage that in the past was provided with: under the state of processing that is not formed, about 1 year timeliness deterioration (phenomenon that YS increases and E1 reduces) do not take place for a long time even at room temperature place yet.

In addition, in the present invention,, there is not any problem, TS, BH, the Δ TS of same levels before demonstrating and plating even implement galvanizing or alloyed hot-dip zinc-coated on the surface of above-mentioned cold-rolled steel sheet of the present invention yet.In addition, as galvanizing and alloyed hot-dip zinc-coated beyond the kind of plating, electro-galvanizing, eleetrotinplate, electrodeposited chromium, electronickelling etc. can both be suitable for well.

Narrated about the 4th of the present invention creating conditions.

At first, adopt generally well-known smelting method such as converter to smelt the steel with following composition: to contain C: less than 0.01%, N:0.0050～0.04%, Al:0.005～0.03%, Si:0.005～1.0%, Mn:0.01～1.5%, P:0.1% be following, below the S:0.01%, or also with B:0.0001～0.003% contain in Nb:0.005～0.050%, Ti:0.005～0.070%, V:0.005～0.10% more than a kind or 2 kinds and N/ (Al+Nb+Ti+V+B): more than 0.30.Then, adopt ingot casting method or continuous metal cast process to make its solidify out into steel ingot.

Make hot-rolled sheet with carrying out hot rolling after this steel ingot heating, the soaking.When Heating temperature (SRT) is crossed when low, processibility to improve effect saturated, and the rolling load during hot rolling increases, and rolling accident takes place or also produce the insufficient danger of homogenizing that causes solid solution N, thus SRT more than 950 ℃ for well.Moreover in order to improve deep-draw ductility, fixedly it is separated out with the carbide form is favourable to solid solution C, and SRT below 1300 ℃ for well.Moreover, in order further to improve processibility, be taken as below 1150 ℃ to well.

If total draft of hot rolled roughing～finish rolling is less than 80%, and then the grain refining of hot-rolled sheet is insufficient, so be defined as more than 80% to well.

When the roughing temperature surpasses 1000 ℃, the grain coarsening of γ → α phase transformation, the r value reduces, as not enough Ar ₃The time because recrystallize alligatoring of α crystal grain or grain growth, make the reduction of r value, so roughing below 1000 ℃, Ar ₃Carry out to good above humidity province.

On the other hand, when surpassing Ar ₃Humidity province when finishing finish rolling, because γ → α phase transformation makes set organize randomization, can not get good deep-draw ductility, on the other hand, when 600 ℃ of less thaies finish finish rolling down, expectation improves less than further deep-draw ductility, and only rolling load increases, so finish rolling is at Ar ₃Below, the humidity province more than 600 ℃ carries out to good.

In addition, when finish rolling, if be not lubricated rolling, then because the effect of the frictional force between roll and the steel plate, additional shear action is in the steel plate skin section, its result the steel plate skin section preferentially form deep-draw ductility unfavorable the 110} position to, so the deep-draw deteriorated ductility.So, carry out to good while finish rolling is lubricated.

Then, hot-rolled sheet is wound into web-like.Moreover, be also referred to as coiled material via the treated material of coiling operation.The coiling temperature (CT) of hot-rolled sheet is high temperature, help the alligatoring of carbide more, but when surpassing 800 ℃, the formed scale thing thickening in hot-rolled sheet surface, the load of removing the operation of scale thing increases, or carries out nitride formation, cause coiled material solid solution N amount fluctuation longitudinally, on the other hand, as if 400 ℃ of less thaies, then winding work becomes difficult.For this reason, CT is taken as 800～400 ℃ for well.

Then, the hot-rolled sheet with gained carries out recrystallization annealing by continuous annealing or annealing at intermittence.Carrying out this annealing (hot-rolled sheet annealing) is that the formed rolling processing set tissue of α district middle temperature rolling that utilization is carried out in finish rolling carries out recrystallize, thereby obtains recrystallize set tissue.

Then, hot-rolled sheet is by the cold rolling cold-reduced sheet that becomes.During cold rolling draft less than 60%, can not expect high r value, on the other hand, when surpassing 95%, instead r value reduces, so is taken as 60～95% for well.

Then, cold-reduced sheet is by recrystallization annealing.This annealing is good in any enterprising behavior of continuous annealing line, continuous hot-dipping zinc wire.Annealing conditions be taken as annealing temperature more than 650 ℃ * hold-time more than 5 seconds for well.If annealing temperature more than 650 ℃, hold-time any more than 5 seconds can not satisfy, then recrystallize can not be finished, and deep-draw ductility reduces.Moreover in order to obtain better deep-draw ductility, preferred annealing temperature is more than 800 ℃ * hold-time is more than 5 seconds.But when annealing temperature surpasses 900 ℃, carry out the dissolving again of carbide, solid solution C exceedingly increases, therefore ageing slowly (anti-room temperature ageing) reduces, and the occasion of generation α → γ phase transformation, randomization is organized in set, and the r value reduces, deep-draw ductility is compromised, so annealing temperature is taken as below 900 ℃ to well.

And then, the cold rolled annealed buttress that cold-rolled steel sheet recrystallization annealing is obtained is implemented galvanizing or implemented Alloying Treatment again according to needs.At this moment, in plating was handled, making the speed of cooling before handle to plating after the recrystallization annealing was more than 5 ℃/second, the plate temperature when making galvanizing be 400～600 ℃ for well, in Alloying Treatment, make treatment temp be 400～600 ℃, treatment time be 5～40 seconds for well.

Moreover cold-rolled steel sheet after the recrystallization annealing or hot-dip galvanized steel sheet also can be with its skin-passes in order to carry out shape correction, adjustment surface smoothness.The draft of this skin-pass is for well below 10%.This is because when this draft surpassed 10%, the r value reduced.

Composition qualification reason about the 5th high strength cold rolled steel plate of the present invention is illustrated.

C：0.0015～0.025％

C gets organizational controls evenly and is fine, in order to ensure the acicular ferrite of q.s, must contain more than 0.0015% in the present invention.On the other hand, when surpassing 0.025%, the carbide mark in the steel plate is excessive, and ductility, r value also have plasticity to reduce significantly.Because this situation, so C is limited in 0.0015～0.025% the scope.Moreover, consider from the viewpoint that improves plasticity, be taken as below 0.020% to well, more preferably below 0.010%.In addition, especially consider that from the viewpoint that makes BH amount and stable material quality C content is taken as better above (12/93) Nb (%) (at this, Nb is Nb content (%)).

Below the Si:1.0%

Si can not make the ductility of steel reduce significantly, and can make the useful element of steel plate high strength, in the present invention, contains more than 0.005% for well, needs high-intensity occasion especially, contains more than 0.10% better.On the other hand, Si makes transformation temperature rise when hot rolling widely, makes the difficulty that becomes of guaranteeing of shape, or the aesthetic property that also gives surface texture, chemical conversion treatment etc., especially surface of steel plate further, produces bad influence to plated film ground with bad influence.In the present invention, be limited to below 1.0%.If Si is below 1.0%, that then above-mentioned bad influence can be suppressed is very low.Moreover, for the purposes of the aesthetic property that especially requires the plated film surface of steel plate, wish that Si is taken as below 0.5%.

Below the Mn:2.0%

Mn is the effective elements that prevents the thermal crack that caused by S, is added to according to the S amount that contains, and in addition, Mn has big effect to the refinement of crystal grain, wishes to add Mn and is used to improve material.From the fixedly viewpoint of S consideration stably, wish that Mn contains more than 0.1%.In addition, Mn is the element that increases armor plate strength, in the occasion of desired strength more, wishes to contain more than 0.5%.Moreover, more preferably more than 0.8%.

When Mn content is brought up to this level, have following big advantage: the discrete quilt with respect to steel plate mechanical properties, the particularly strain-aged hardening characteristics of the fluctuation of hot-rolled condition improves significantly.; when excessively containing Mn and surpass 2.0%; though detailed mechanism is unclear; but has the trend that increases the thermal distortion drag; the trend of deterioration weldability, welding zone plasticity is arranged in addition, and then suppress ferritic generation significantly, ductility reduces significantly; the tendency of r value reduction also becomes significantly in addition, so Mn is limited to below 2.0%.In the purposes that requires better solidity to corrosion and plasticity, be taken as below 1.5% to well.

Below the P:0.1%

P is as the solution strengthening element of steel and useful element, considers from the viewpoint of gaining in strength, and contains more than 0.002% for well, especially needs high-intensity occasion, preferably contains more than 0.02%.On the other hand, when excessively containing, make the steel embrittlement, and then worsen the crimping processibility of steel plate.In addition, because P tendency of segregation in steel is strong, result from its embrittlement of welding zone so cause.Therefore, P is limited to below 0.1%.Moreover in especially paying attention to crimping processibility and welding zone flexible purposes, P is taken as below 0.08% to well.More preferably below 0.06%.

Below the S:0.02%

S is that the form with inclusion exists in steel plate, and the ductility of steel plate is reduced, and also causes the element of solidity to corrosion deterioration, is reduced to as far as possible, and in the present invention, S is limited to below 0.02%.Especially for the purposes that requires good processibility, S is taken as below 0.015% to well.In addition, in the occasion that requires good especially crimping processibility, S is taken as below 0.010% to well.In addition, though detailed mechanism is unclear, for the strain-aged hardening characteristics with steel plate stably maintains high level, it is effective that S is reduced to below 0.008%.

Below the Al:0.02%

Al works as reductor, and the purity of steel is improved, and also the element of the tissue of refinement steel plate in the present invention, wishes to contain more than 0.001%.In the present invention, the N of solid solution attitude is utilized as strengthening element, but contain the aluminium killed steel and the rimming steel ratio in the past that does not add Al of the Al of proper range, its mechanical properties is good.On the other hand, contain superfluous Al the surface texture of steel plate is worsened, the N of solid solution attitude is reduced significantly, be difficult to obtain great strain-age hardening amount as emphasis point of the present invention.Because this situation, so in the present invention, Al is limited to below 0.02%.Moreover, consider from the viewpoint of the stability of material, wish that more making Al is 0.001～0.015%.In addition, reducing Al content and also worry grain coarsening, but in the present invention, is optimum quantity and to make annealing conditions be best scope by making other alloying elements, promptly prevents this situation effectively.

N：0.0050～0.0250％

N is the element that armor plate strength is increased by solution strengthening and strain-age hardening, is most important element in the present invention.In addition, in the present invention,, also resemble and Al content is adjusted into appropriate value above-mentioned, also control hot-rolled condition, annealing conditions etc. and create conditions, make and in cold rolling goods or plated product, guarantee essential and the N of solid solution attitude fully by containing an amount of N.In view of the above, can give full play to the intensity (yielding stress and tensile strength) that produces by solution strengthening and strain-age hardening and go up ascending effect, can obtain stably that the target value of the mechanical properties of following steel plate of the present invention: tensile strength 340MPa is above, baking hardening amount (BH amount) 80MPa is above, handle in strain aging more than the increasing amount Δ TS 40MPa of tensile strength of front and back.In addition, N has the effect that reduces transformation temperature, and it is effective containing under the occasion of the rolling grade of not wanting the thin thing that is rolled that reduces transformation temperature widely.

During N less than 0.0050%, ascending effect is difficult to stably manifest on the above-mentioned intensity.On the other hand, when N surpassed 0.0250%, the subsurface defect incidence of steel plate uprised, the slab crackle when continuous casting taking place simultaneously etc. morely.Therefore, N is limited to 0.0050～0.0250% scope.Moreover from the stability of having considered the material that manufacturing process is overall, the viewpoint that qualification rate improves, N is preferably 0.0070～0.0200%, more preferably 0.0100～0.0170% scope.Moreover, if be N amount in the scope of the invention, then fully not to the bad influence of weldability etc.

More than the N:0.0010% of solid solution attitude

In cold rolling goods, in order to ensure full intensity, and bring into play the strain-age hardening that causes by N effectively, in steel plate, must there be the N (also being solid solution N) of the solid solution attitude more than 0.0010% at least.

At this, solid solution N amount is that the total N content from steel deducts and separates out the N amount, and income value is measured as solid solution N.Moreover as separating out N quantitative analysis method, the inventor compares, has studied the whole bag of tricks, the result, and utilization has been used the electrolytic extracting process of constant potential electrolytic process and obtained is effective.Moreover, be used to extract the method for the iron matrix of analysis as dissolving, acid decomposition, halogen method and electrolytic process are arranged.Wherein, electrolytic process can not decomposed extremely unsettled precipitates such as carbide, nitride, can only stably dissolve iron matrix.Use methyl ethyl diketone system, electrolysis under constant potential as electrolytic solution.In the present invention, the result who uses constant potential electrolytic process mensuration to separate out the N amount demonstrates with actual material and changes well corresponding.

Because this situation in the present invention, will adopt the residue of constant potential electrolytic process extraction to carry out chemical analysis, obtain the N amount in the residue, and it is measured as separating out N.

Moreover, in the occasion of the higher BH of needs amount, Δ TS, make solid solution N amount be more than 0.0020% for well, in order to obtain higher value, be taken as more than 0.0030% to well.The higher limit of solid solution N amount does not limit especially, even but the reduction of the whole residual mechanical propertiess of total N content is also little.

The N/Al ratio of Al content (the N content with): more than 0.3

Under the goods state, for residual solid solution N more than 0.0010% stably, must restriction as the amount of the Al of the element of strong fix N.Steel plate about the combination that changed N content (0.0050～0.0250%) in the compositing range of the present invention and Al content (below 0.02%) in wide region is studied, the result as can be known, by making N/Al is more than 0.3, and can stably make the solid solution N in cold rolling goods and plated film goods is more than 0.0010%.Therefore, N/Al is limited to more than 0.3.Moreover from stably improving the viewpoint of strain-aged hardening characteristics, N/Al is for well more than 0.6.More preferably more than 0.8.

Nb：0.002～0.050％

Nb and B are compound, play useful effect mutually to generating acicular ferrite, in the present invention, must contain more than 0.002%.On the other hand, when content surpassed 0.050%, its effect was saturated, and the thermal distortion drag significantly increases, the hot rolling difficulty that becomes.Therefore, Nb is limited to 0.002～0.050% with in the scope.Moreover, more preferably 0.005～0.040%.

B：0.0001～0.0050％

B is compound with Nb, to generating the element that acicular ferrite plays a role mutually effectively, in the present invention, must contain more than 0.0001%.On the other hand, when content surpasses 0.0050%, the solid solution N that helps strain-aged hardening characteristics is reduced.Therefore, B is limited in 0.0001～0.0050% the scope.Moreover, preferred 0.0003～0.0030%.More preferably 0.0005～0.0030%.

In the present invention, on above-mentioned composition basis, it is above for well also to contain in the following a group～c group 1 group or 2 groups, wherein,

The a group: more than a kind or 2 kinds of Cu, Ni, Cr, Mo, total amount are below 1.0%;

The b group: more than a kind or 2 kinds of Ti, V, total amount are below 0.1%;

C group: Ca, REM a kind or 2 kinds, the total amount is 0.0010～0.010%.

A group element: Cu, Ni, Cr, Mo are the elements that helps armor plate strength to rise, and can select as required, independent or compound containing.This effect can be seen when containing Cu, Ni more than 0.01%, Cr, Mo respectively., when content was too much, the thermal distortion drag increased, and perhaps chemical surface treatment and generalized surface treatment characteristics worsen, and the welding zone sclerosis, welding zone plasticity deterioration.Therefore, Cu, Ni, Cr, Mo are taken as respectively below 1.0%, below 1.0%, below 0.5%, below 0.2% individually to well.Containing sometimes compoundly, adding up to that to measure be for well below 1.0%.

B group element: Ti, V are the elements that helps the grain refining homogenizing, can select as required, independent or compound containing.This effect can be seen when Ti, the V that contains respectively more than 0.005%., when content was too much, the thermal distortion drag increased, and chemical surface treatment and generalized surface treatment characteristics worsen simultaneously.Further, the bad influence that reduces solid solution N is also arranged.Therefore, Ti, V are taken as respectively below 0.1%, below 0.1% individually to well.Contain sometimes compound, add up to that to measure be for well below 0.1%.

C group element: Ca, REM are the elements that the control inclusion morphology is worked, and especially in the occasion that requires the crimping plasticity, to contain promising good independent or compoundly.When the total quantity not sufficient 0.0010% of d group element, the effect deficiency of control inclusion morphology, on the other hand, when surpassing 0.010%, becoming of surface imperfection is remarkable.Therefore, the d group element to be limited to the total amount be 0.0010～0.010% scope for well.In view of the above, can not be attended by the generation of surface imperfection, can improve the crimping processibility.

Tissue about steel plate of the present invention is illustrated.

Steel plate of the present invention represents to have the tissue that is made of phase of the acicular ferrite more than 5% and the ferritic phase below the average size of microcrystal 20 μ m with area occupation ratio.

The area occupation ratio of acicular ferrite phase: more than 5%

Cold-rolled steel sheet of the present invention is represented with area occupation ratio, contains the acicular ferrite phase more than 5%.By there being the acicular ferrite more than 5%, can obtain good ductility and big strain-age hardening amount.Though detailed mechanism is unclear, can infer this be because: by there being the acicular ferrite phase, the prestrain before timeliness adds man-hour, answer pole-changing effectively in inside by the accumulative cause.Again, the existence of acicular ferrite phase improves timeliness deterioration at normal temperatures, to reach normal temperature non-ageing also be effective.Moreover in order to obtain good intensity-ductility balance, higher intensity, the area occupation ratio that makes the acicular ferrite phase is for well more than 10%.Moreover, the problem that has reduction r value of the acicular ferrite phase of volume above 20%.Therefore, the area occupation ratio of acicular ferrite phase is more than 5%, and is preferred more than 10%, below 20%.

Said in the present invention acicular ferrite is to resemble the ultra low-carbon steel peculiar low temperature phase change phase that in inside do not have carbide of the present invention forming mutually, mainly can distinguish clearly with common polygonization ferrite by observation by light microscope, be inner dislocation desity height, the phase harder than polygonization ferritic phase.

According to observation by light microscope, the acicular ferrite of following several forms distributes mutually independent or compoundly: 1. crystal boundary has the grains of irregular corner angle; 2. along the crystal boundary of precipitate and so on and the grains that exists; 3. be and scratch the grains of hindering the shape pattern or crystal grain group shape (majority can be seen subgrain boundary in the 2nd bigger phase particle) etc.They can be distinguished clearly with common polygonization ferrite.In addition, the intragranular tone that is corroded is also different with martensite and bainite, with the common basic no change of polygonization ferrite, so also can distinguish clearly with martensite and bainite.According to the observation of transmission electron microscope, the crystal boundary of acicular ferrite phase is neighbouring and/or intragranular dislocation desity is very high, and particularly 3. the acicular ferrite of form part that its dislocation desity is very high mutually and lower part become stratiform.

Cold-rolled steel sheet of the present invention is an object with the automotive sheet of demanding plasticity, and in order to ensure ductility, beyond the acicular ferrite phase is ferritic phase mutually.When the area occupation ratio less than 80% of ferritic phase, guarantee as the necessary ductility of the automotive sheet that requires processibility, the high r value difficulty that becomes.Moreover, requiring better ductile occasion, the area occupation ratio of wishing ferritic phase is more than 80%, more preferably more than 85%.Moreover said in the present invention ferrite is meant the not so-called polygonization ferrite of residual strain state.

The average crystal grain particle diameter of ferritic phase: below the 20 μ m

In the present invention, as the average crystal grain particle diameter is to adopt from the section structure photo to utilize nominal diameter that value that the planimetry of ASTM regulation calculates and the process of chopping of utilizing same ASTM regulation obtain (for example, with reference to Mei Ben etc.: thermal treatment, 24 (1984), 334) among bigger person.

Cold-rolled steel sheet of the present invention, guarantee the solid solution N amount of defined amount in the goods stage, but according to the inventor's experimental study, even have the steel plate of the solid solution N of same amount, sometimes strain-aged hardening characteristics also produces discretely, has distinguished that one of its main essential factor is a size of microcrystal.Tissue of the present invention is below the 20 μ m at least, is preferably below the 15 μ m by making its average crystal grain particle diameter, can stably obtain high BH amount, Δ TS.Though detailed mechanism is unclear, can be speculated as: with alloying element to the segregation of crystal boundary, separate out and processing, thermal history relevant to their influence.

Therefore, in order to seek the stabilization of strain-aged hardening characteristics, the average crystal grain particle diameter that makes ferritic phase is below the 20 μ m, below the preferred 15 μ m.

Cold-rolled steel sheet of the present invention with above-mentioned composition and tissue, have tensile strength (TS) 340MPa above, below about 590MPa, and to have the r value be high r value and good strain-aged hardening characteristics more than 1.2.TS can not be widely used on the member with structural member key element less than the steel plate of 340MPa.In addition, in order further to enlarge the scope of application, wish that TS is more than the 400MPa.In addition, if r value less than 1.2 then can not be applicable to large-scale drawing parts.Moreover the preferable range of r value is more than 1.3.

The baking processing condition of spraying paint in the past adopts 170 ℃ * 20 minutes as standard.Moreover, the steel plate of the present invention of the solid solution N that contains volume is applied strained occasion more than 5%, even more demulcent (low temperature one side) processing also can reach sclerosis, in other words, acquisitive prescription condition more broadly.In addition, in general, in order to strive for hardening capacity, in not because of overaging remollescent limit, keeping under high temperature more is favourable for more time.

Narration particularly, steel plate of the present invention is about 100 ℃ at the become lower limit of significant Heating temperature of predeformation post-hardening.On the other hand, when Heating temperature surpassed 300 ℃, sclerosis culminated, and occurs remollescent trend a little on the contrary, and in addition, becoming of thermal strain and tempering color is remarkable.In addition, about the hold-time, if more than being about about 30 seconds during 200 ℃ of left and right sides of Heating temperature, then can reach sufficient sclerosis substantially.In order to obtain bigger stable sclerosis, the preferred hold-time is more than 60 seconds., when the hold-time surpasses 20 fens kinds, not only can not further be hardened, and production efficiency also significantly reduces, unfavorable aspect practical.

Thus, in the present invention, be decided to be: with 170 ℃, the hold-time of evaluation in 20 minutes as the Heating temperature of the baking processing condition of spraying paint in the past as the ageing treatment condition.Even the baking-type steel plate that sprays paint in the past can not reach under the ageing treatment condition of sufficient hardened low-temperature heat short period of time maintenance, steel plate of the present invention also can stably reach big sclerosis.Moreover the method for heating is restriction especially, removes atmosphere that the stove that adopted by the common baking of spraying paint carries out heats, and for example, the heating of being undertaken by induction heating, non-oxidation flame, laser, plasma etc. etc. all can be adopted well.

Automobile must be able to be resisted stress-loaded from the complexity of outside with strength of parts, so sheet stock is important in the strength characteristics of little strain regions not only, and also is important in the strength characteristics of bigger strain regions.The inventor is according to this point, make the BH amount (corresponding to the strength characteristics of smaller strain regions) that will become the raw-material steel plate of the present invention of trolley part for more than the 80MPa, make Δ TS amount (corresponding to the strength characteristics of bigger strain regions) simultaneously for more than the 40MPa.Moreover more preferably the BH amount is for 100MPa is above, Δ TS is more than the 50MPa.In addition, the Heating temperature by with ageing treatment the time is set in more high temperature one side and/or will be set in longer time one side the hold-time, can make BH amount and Δ TS bigger.

Even effect of the present invention also can be brought into play when the sheet thickness rate is thicker, but when the goods thickness of slab surpasses 3.2mm, in the cold-reduced sheet annealing operation, can not guarantee essential speed of cooling fully, when continuous annealing, produce strain aging, be difficult to obtain strain-aged hardening characteristics as the goods target.Therefore, the thickness of slab of steel plate of the present invention below 3.2mm for well.

In addition, in the present invention, even do not have any problem in execution plating of the surface of above-mentioned cold-rolled steel sheet of the present invention or hot dip process yet.These plated film steel plates also demonstrate and TS, the BH amount of plating preceding the same degree, Δ TS amount.As the kind of plated film, electro-galvanizing, galvanizing, alloyed hot-dip zinc-coated, eleetrotinplate, electrodeposited chromium, electronickelling etc. can both finely be used.

Manufacture method about the 6th steel plate of the present invention is illustrated.

Steel plate of the present invention is made by implementing following operation successively basically: the plate slab heating back roughing that will have the composition of above-mentioned scope, base laminates, this thin slab is implemented finish rolling, thereby postcooling is finished in finish rolling, the hot-rolled process of making hot-rolled sheet of reeling, this hot-rolled sheet is implemented pickling and the cold rolling cold-reduced sheet annealing operation of making the cold rolling process of cold-reduced sheet, this cold-reduced sheet being carried out continuous annealing.

The slab that uses in manufacture method of the present invention will prevent the macrosegregation of composition, wishes to adopt the continuous metal cast process manufacturing, but also can adopt ingot casting method, the manufacturing of thin slab casting.In addition, after making slab, except the method always of cool to room temperature for the time being and then heating, do not cool off the dead-beat that just is encased in process furnace and is rolled with hot base state rolling or heat a little after the energy-conservation technology such as direct rolling that directly is rolled also can the use of no problem ground.Particularly in order to guarantee the N of solid solution attitude effectively, dead-beat is rolling to be one of useful technology.

At first, the term restriction reason about hot-rolled process is illustrated.

Slab heating temperature: more than 1000 ℃

Slab heating temperature in order to ensure as A-stage must and fully solid solution N amount, satisfy the target value of the solid solution N amount in goods, be taken as more than 1000 ℃ to well.Moreover, because along with the increase loss of oxidation weight increases, so be taken as below 1280 ℃ to well.

Jia Re slab is by the roughing base that laminates under these conditions.Moreover the condition of roughing needn't special stipulation, as long as according to ordinary method., consider, wish to carry out with the short period of time as far as possible from the viewpoint of guaranteeing solid solution N amount.Then the planished sheet base is made hot-rolled sheet.

Moreover, in the present invention, between roughing and finish rolling, wish that the thin slab that front and back are adjacent is engaged with each other, continuous rolling.Use pressure welding method, method of laser welding, electron beam welding connection etc. for well as engagement means.

By continuous rolling, the so-called rolling non-constant part of the front-end and back-end of coiled material (processed material) becomes and does not have, and stable hot-rolled condition spreads all over coiled material (processed material) total length and overall with becomes possibility.This also is extremely effective not only to hot-rolled steel sheet to cross-sectional shape and the size of improving cold-rolled steel sheet.In addition, rolling after, cooling the time also can give tension force on hot run table, so can keep the steel plate shape well.

In addition,, the coiled material front end is stably passed through, in the unit of each common thin slab is rolling, can use the unworkable lubrication and rolling of problem because of sheet material trafficability characteristic and engaging-in property for by carrying out tandem rolling.Can reduce rolling load in view of the above, also can reduce the surface pressure of roll simultaneously, can prolong the life-span of roll.

In addition, in the present invention, finishing mill between roughing and finish rolling is imported a side, use add hot thin slab width end thin slab edges of boards well heater, add any one party or two sides in the thin slab well heater of hot thin slab length direction end, the uniformity of temperature profile that makes thin slab width and length direction is for well.In view of the above, the material that can further reduce in the steel plate is discrete.Thin slab edges of boards well heater, thin slab well heater are induction heating mode for well.

Use wishes at first to adopt the temperature head of thin slab edges of boards well heater compensation width in proper order.The heat that adds of this moment also is based on steel and forms, but the width temperature distribution scope that finish rolling goes out material one side be set at about below 20 ℃ for well.Then utilize the temperature head of thin slab well heater compensating length direction.This moment add heat set for the length end region temperature than central area temperature high approximately about 20 ℃ for good.

Finish rolling goes out the material temperature: more than 800 ℃

In order to obtain evenly fine hot rolling motherboard tissue, finish rolling goes out material temperature FDT and is taken as more than 800 ℃.When FDT was lower than 800 ℃, the tissue of steel plate became inhomogeneous, and partly the residual process tissue can not be eliminated and left behind through the ununiformity of organizing after the cold rolled annealed operation.Therefore, when to avoid worked structure residual, when adopting high coiling temperature, produce coarse grain, same unfavorable condition takes place.In addition, be high temperature by making the coiling temperature, the remarkable reduction of solid solution N amount takes place, therefore be difficult to obtain tensile strength as more than the purpose 340MPa.Because this situation, finish rolling goes out material temperature FDT and is taken as 800 ℃.In order further to improve mechanical properties, wish that making FDT is more than 820 ℃.Moreover, consider that from the viewpoint that improves the r value FDT is Ac ₃Transformation temperature is above better.In addition, the not special stipulation of the upper limit of FDT, but when exceedingly high, scale thing defective etc. become remarkable.Moreover FDT is taken as approximately about 1000 ℃ for well.

Coiling temperature: below 800 ℃

Along with the reduction of coiling temperature CT, there is the trend that increases in armor plate strength.More than target tensile strength TS340MPa, CT is taken as below 800 ℃ to well.Moreover when 200 ℃ of CT less thaies, the steel plate shape is irregular easily, in the actually operating, produces the dangerous high of unfavorable condition, demonstrates the tendency that the material homogeneity reduces.Therefore, wish that CT is taken as more than 200 ℃.Moreover, more requiring the inhomogeneity occasion of material, CT is taken as more than 300 ℃ to well.More preferably more than 350 ℃.

In addition, in the present invention, when finish rolling,, also can be lubricated rolling in order to reduce hot rolling load.Rolling by being lubricated, the shape material effect of uniform more that makes hot-rolled sheet is arranged.Moreover, the frictional coefficient during lubrication and rolling in 0.25～0.10 scope for well.In addition, the rolling and continuous rolling by combined lubrication, the hot rolled operation is stable.

The hot-rolled sheet of having implemented above-mentioned hot-rolled process is implemented pickling and cold rolling then by cold rolling process, makes cold-reduced sheet.

The condition of pickling gets final product with generally well-known condition, does not limit especially.Moreover, in the scale thing occasion as thin as a wafer of hot-rolled sheet, also can not implement pickling and directly carry out cold rolling.

In addition, cooling conditions gets final product with generally well-known condition, does not limit especially.Moreover, consider that from the viewpoint of guaranteeing homogeneity of structure cold rolling draft is taken as more than 60% to well.Below illustrated about the term restriction reason of cold-reduced sheet annealing operation.

Cold-reduced sheet is then implemented the cold-reduced sheet annealing operation that is made of continuous annealing-cooling.

Continuous annealing temperature: the temperature in ferrite-austenite two-phase coexistence

By annealing under the temperature in ferrite-austenite two-phase coexistence, form the acicular ferrite phase.And, in ferritic phase (111) set organize also very flourishing, so can obtain high r value.On the other hand, become under the high temperature of austenite one phase surpassing ferrite-austenite two-phase coexistence, by reverse transformation and phase transformation, randomization is organized in the set of steel plate, so the r value reduces.For this reason, in the present invention, the annealing temperature of continuous annealing is limited to temperature in the above ferrite of recrystallization temperature-austenite two-phase coexistence.Moreover, consider from the stability of r value, be taken as austenitic mark and be more than 10%～50% temperature when following is for well.

In addition, the hold-time of continuous annealing time from production efficiency, thinning microstructure, guarantee that the viewpoint of solid solution N amount considers, short in as much as possible well.Consider that from the viewpoint of the stability of operation the hold-time is for well more than 10 seconds.In addition, from thinning microstructure with guarantee that the viewpoint of solid solution N amount considers, be taken as below 90 seconds to well.Moreover, consider from the viewpoint of the stabilization of material, be taken as more than 20 seconds better.

Cooling after the continuous annealing: be cooled to humidity province below 500 ℃ with 10～300 ℃/second speed of cooling

Cooling after the soaking in the continuous annealing from thinning microstructure, form the acicular ferrite phase, guarantee the viewpoint of solid solution N amount considers it is important.In the present invention, supersign is cooled to humidity province below 500 ℃ continuously with the speed of cooling more than 10 ℃/second.When 10 ℃/second of speed of cooling less thaies, can not obtain the acicular ferrite amount of necessary amounts, even and fine tissue and the solid solution N of q.s.On the other hand, when speed of cooling surpassed 300 ℃/second, steel plate was at the lack of uniformity of the material of width.In addition, when the cooling under 10～300 ℃/second the speed of cooling after continuous annealing stops temperature above 500 ℃, can not realize the refinement of organizing.

Skin-pass or leveling processing: unit elongation 0.5～10%

In the present invention, continue,, also can implement the processing of skin-pass or leveling for the purpose of correcting shape, adjustment smooth finish with cold rolled annealed operation.When the unit elongation of skin-pass or leveling processing adds up to quantity not sufficient 0.5%, can not reach the purpose of correcting shape, adjusting smooth finish.On the other hand, when surpassing 10%, cause ductility to reduce.Moreover, consider from guaranteeing the ductile viewpoint, be taken as below 5% better.In addition, for skin-pass and leveling processing, its form processing difference, both do not have big difference but confirmed its effect.Even skin-pass, leveling processing also are effective after coating film treatment.

Composition qualification reason about the 7th high strength cold rolled steel plate of the present invention is illustrated.

C：0.025～0.15％

C is the element that increases armor plate strength, in addition, in order evenly and imperceptibly to control the tissue as important composition prerequisite of the present invention, guarantees the martensitic phase of q.s, must contain more than 0.025%.On the other hand, when surpassing 0.15%, the carbide mark in the steel plate is excessive, ductility, also has plasticity to reduce significantly.Again, as prior problem, when C content surpassed 0.15%, spot-welded on, electric-arc welding weldability etc. significantly reduced.Because this situation, C is limited in 0.025～0.15% the scope.Moreover, consider from the viewpoint that improves plasticity, be taken as below 0.08% to well.In addition, in requiring good especially ductile purposes, be taken as below 0.05% better.

Below the Si:1.0%

Si is that the ductility that does not make steel significantly reduces, can make the useful nothing of steel plate high strength plain, preferably contains more than 0.005%, more preferably contains more than 0.1%.On the other hand, Si rises transformation temperature when hot rolling greatly, is difficult to guarantee quality, shape, or the aesthetic property that also gives surface texture, chemical surface treatment etc., especially surface of steel plate is with bad influence, and then bring bad influence also for plated film, in the present invention, be limited to below 1.0%.If Si below 1.0%, then can suppress above-mentioned bad influence very low.Moreover, low in the requirement of strength rank, particularly require on the purposes of surface aesthetic, wish that Si is taken as below 0.5%.

Below the Mn:2.0%

Mn is the effective element that prevents the thermal crack that caused by S, is added to according to the S amount that contains, and Mn has big effect to the refinement of crystal grain in addition, wishes to add it and is used to improve material.During the quick cooling of Mn after continuous annealing, be for making martensite stably generate utmost point effective elements again.From the fixing viewpoint of S stably, wish that Mn contains more than 0.2%.In addition, Mn is the element that increases armor plate strength, in the occasion that requires the super intensity of TS 500MPa, wishes to contain more than 1.2%.More preferably more than 1.5%.

When Mn content was brought up to this level, the big advantage that has was: the discrete quilt with respect to mechanical properties, the particularly strain-aged hardening characteristics of the steel plate of the fluctuation of hot-rolled condition improves significantly., when excessively containing Mn and surpass 2.0%, be difficult to obtain the high r value as one of important prerequisite of the present invention, while ductility reduces significantly, so Mn is limited to below 2.0%.In the purposes that requires better solidity to corrosion and plasticity, be taken as below 1.7% to well.

Below the P:0.08%

P is as the solution strengthening element of steel and useful element, considers from the viewpoint that intensity increases, and contains 0.001% or more for well, contains more than 0.015% better.On the other hand, when excessively containing, make the steel embrittlement, also worsen the crimping processibility of steel plate.Therefore in addition, P tendency of segregation in steel is strong, causes to result from this embrittlement of welding zone.Therefore P is limited to below 0.08%.Moreover, paying attention in crimping processibility and the welding zone flexible purposes special, P is taken as below 0.04% to well.

Below the S:0.02%

There is, reduces the ductility of steel plate in S, also causes the element of solidity to corrosion deterioration with the inclusion form in steel plate, is reduced to as far as possible, and in the present invention, S is limited to below 0.02%.Particularly on the purposes that requires good processibility, S is taken as below 0.015% to well.In addition, in the occasion that requires good especially crimping processibility, S is taken as below 0.008% to well.In addition, though detailed mechanism is unclear, for the strain-aged hardening characteristics with steel plate stably maintains high level, it is effective that S is reduced to below 0.008%.

Below the Al:0.02%

Al plays a role as reductor, improves the purity of steel, the element of the tissue of refinement steel plate also, in the present invention, wishes to contain more than 0.001%.In the present invention, the N of solid solution attitude is utilized as strengthening element, but the aluminium killed steel that contains the Al of proper range compares with the rimming steel in the past that does not add Al, its mechanical properties is good.On the other hand, contain the surface texture that superfluous Al will worsen steel plate, also reduce the N of solid solution attitude significantly, be difficult to obtain great strain-age hardening amount.Because this situation, in the present invention, Al is limited to below 0.02%.Moreover, consider that from the viewpoint of the stability of material Al is taken as 0.001～0.015% for well.In addition, reduce Al content and also might bring grain coarsening, but in the present invention, by other alloying elements being limited in optimum quantity, making annealing conditions, thereby prevented this situation effectively at optimum range.

N：0.0050～0.0250％

N is the element that armor plate strength is increased by solution strengthening and strain-age hardening, is most important element in the present invention.In addition, in the present invention, by containing an amount of N, and resemble and Al content is adjusted into appropriate value above-mentioned, and control hot-rolled condition, annealing conditions etc. create conditions, guarantee in cold rolling goods or plated film goods institute must and the N of enough solid solution attitude.In view of the above, can give full play to the intensity (yielding stress and tensile strength) brought by solution strengthening and strain-age hardening and go up ascending effect, can obtain stably that the target value of the mechanical properties of following steel plate of the present invention: tensile strength 440MPa is above, baking hardening amount (BH amount) 80MPa is above, handle more than the tensile strength increasing amount Δ TS 40MPa of front and back in strain aging.

When N less than 0.0050%, ascending effect is difficult to stably manifest on the above-mentioned intensity.On the other hand, when N surpassed 0.0250%, the subsurface defect incidence of steel plate uprised, and the slab crackle during continuous casting etc. also more simultaneously a generation.Therefore, N is limited to 0.0050～0.0250% scope.Moreover from the stability of having considered the raising material that manufacturing process is overall, the viewpoint of qualification rate, N is preferably 0.0070～0.0170%.Moreover, if be N amount in the scope of the invention, then fully not to the bad influence of weldability etc.

More than the N:0.0010% of solid solution attitude

In cold rolling goods, in order to ensure full intensity, and bring into play the strain-age hardening that causes by N effectively, in steel plate, must there be the N (also being solid solution N) of the solid solution attitude more than 0.0010% at least.

At this, solid solution N amount is that the total N content from steel deducts and separates out the N amount, and income value is measured as solid solution N.Moreover as separating out N quantitative analysis method, the inventor compares, has studied the whole bag of tricks, the result, and employing has been used the electrolytic extracting process of constant potential electrolytic process and obtained is effective.Moreover, be used to extract the method for the iron matrix of analysis as dissolving, acid decomposition, halogen method and electrolytic process are arranged.Wherein, electrolytic process can not decomposed extremely unsettled precipitates such as carbide, nitride, can only stably dissolve iron matrix.Use methyl ethyl diketone system, electrolysis under constant potential as electrolytic solution.In the present invention, the result who uses constant potential electrolytic process mensuration to separate out the N amount demonstrates with actual material and changes well corresponding.

Because this situation in the present invention, will adopt the residue of constant potential electrolytic process extraction to carry out chemical analysis, obtain the N amount in the residue, and it is measured as separating out N.

Moreover, in the occasion of the higher BH of needs amount, Δ TS, make solid solution N amount be more than 0.0020% for well, in order to obtain higher value, be taken as more than 0.0030% to well.The higher limit of solid solution N amount does not limit especially, even but the reduction of the whole residual mechanical propertiess of total N content of adding is also little.

The N/Al ratio of Al content (the N content with): more than 0.3

Under the goods state, for residual solid solution N more than 0.0010% stably, must restriction as the amount of the Al of the element of strong fix N.Steel plate about the combination that changed N content (0.0050～0.0250%) in the compositing range of the present invention and Al content (below 0.02%) in wide region is studied, the result as can be known, by making N/Al is more than 0.3, and can stably make the solid solution N in cold rolling goods and plated film goods is more than 0.0010%.Therefore, N/Al is limited to more than 0.3.

In the present invention, on above-mentioned composition basis, it is above for well also to contain in the following d group～g group 1 group or 2 groups, wherein,

The d group: more than a kind or 2 kinds of Cu, Ni, Cr, Mo, total amount are below 1.0%;

The e group: more than a kind or 2 kinds of Nb, Ti, V, total amount are below 0.1%;

F group: the B below 0.0030%;

G group: Ca, REM a kind or 2 kinds, the total amount is 0.0010～0.010%.

D group element: Cu, Ni, Cr, Mo are the elements that helps armor plate strength to rise, and can select as required, independent or compound containing.This effect can be seen when containing Cu, Ni more than 0.005%, Cr, Mo respectively., when content was too much, the thermal distortion drag increased, and perhaps chemical surface treatment and generalized surface treatment characteristics worsen, and the welding zone sclerosis, welding zone plasticity deterioration.The r value also has the tendency of reduction in addition.Therefore, the element total amount of a group is for well below 1.0%.Moreover, contain to the Mo volume 0.05% when above, the r value is reduced significantly.When containing Mo in the present invention, be limited to less than 0.05% for well.

E group element: Nb, Ti, V are the elements that helps the grain refining homogenizing, can select as required, independent or compound containing.This effect can be seen when containing Nb, Ti more than 0.005%, V respectively., when content was too much, the thermal distortion drag increased, and chemical surface treatment and generalized surface treatment characteristics worsen simultaneously.Therefore, b group element total amount is for well below 0.1%.

F group element: B is the element with effect of the hardening capacity that improves steel, and the purpose for the mark increase that makes ferritic phase low temperature phase change phase in addition, increase hardness of steel can contain as required.This effect can be seen when the B that contains more than 0.0005%., when equivalent was too much, thermal distortion can reduce, and owing to generating BN solid solution N was reduced.Therefore, B is taken as below 0.0030% to well.

G group element: Ca, REM are the elements that the control inclusion morphology is worked, and especially in the occasion that requires the crimping plasticity, to contain promising good independent or compoundly.At this moment, when the total quantity not sufficient 0.0010% of d group element, the effect deficiency of control inclusion morphology, on the other hand, when surpassing 0.010%, becoming of surface imperfection is remarkable.Therefore, the d group element to be limited to the total amount be 0.0010～0.010% scope for well.In view of the above, can not be attended by the generation of surface imperfection, can improve the crimping processibility.

Tissue about steel plate of the present invention is illustrated below.

The area occupation ratio of ferritic phase: more than 80%

Cold-rolled steel sheet of the present invention is an object with the automotive sheet that requires processibility to a certain degree, in order to ensure ductility, formation contains the tissue of the ferritic phase of representing with area occupation ratio more than 80%, when the area occupation ratio less than 80% of ferritic phase, be difficult to guarantee the necessary ductility of automotive sheet as requiring processibility.Moreover, requiring better ductile occasion, the area occupation ratio of wishing ferritic phase is more than 85%.Moreover said in the present invention ferrite is meant the not so-called polygonization ferrite of residual strain state.

The average crystal grain particle diameter of ferritic phase: below the 10 μ m

In the present invention, as the average crystal grain particle diameter, be to adopt from the section structure photo to utilize the nominal diameter that value that the planimetry of ASTM regulation calculates and the process of chopping of utilizing same ASTM regulation obtain (for example, with reference to Mei Ben etc.: thermal treatment, 24 (1984), 334) the bigger person among.

Cold-rolled steel sheet of the present invention, guarantee the solid solution N amount of defined amount in the goods stage, but according to the inventor's experimental study, even have the steel plate of the solid solution N of same amount, sometimes strain-aged hardening characteristics also produces discretely, has distinguished that one of its main essential factor is a size of microcrystal.Tissue of the present invention by making the average crystal grain particle diameter at least below the 10 μ m, below the preferred 8 μ m, can stably obtain high BH amount, Δ TS.Though detailed mechanism is unclear, can be speculated as: with alloying element to the segregation of crystal boundary, separate out and processing, thermal history relevant to their influence.

Therefore, in order to seek the stabilization of strain-aged hardening characteristics, the average crystal grain particle diameter that must make ferritic phase is below the 10 μ m, below the preferred 8 μ m.

As described above, in order to ensure as the ductility of automotive sheet and the stabilization of seeking strain-aged hardening characteristics, form in the present invention that to contain the average crystal grain particle diameter of representing with area occupation ratio more than 80% be ferritic tissue below the 10 μ m.

The area occupation ratio of martensitic phase: more than 2%

Cold-rolled steel sheet of the present invention contains the martensite of representing with area occupation ratio as the 2nd phase more than 2%.By there being the martensite more than 2%, can obtain good ductility, bigger strain-age hardening.Though detailed mechanism is unclear, can infer it is because, put aside the strained cause effectively in internal poles because the existence of martensitic phase makes that the prestrain before timeliness adds man-hour.Again, the existence of martensitic phase also is effective to improving the timeliness deterioration.Moreover in order to obtain good intensity-ductility balance, low yielding ratio, the area occupation ratio that makes martensitic phase is for well more than 5%.Moreover having of the martensitic phase of the volume above 20% reduces the ductile problem.Therefore, the area occupation ratio of martensitic phase is more than 2%, and is preferred more than 5%, below 20%.

As the 2nd phase, except that above-mentioned martensitic phase, exist perlite, bainite, residual austenite also not to have what problem, be 2% or more but must make the ferritic phase mark be in the present invention, make the martensitic phase mark more than 80%.The total area occupation ratio of perlite, bainite, residual austenite is limited to less than 18%.

Cold-rolled steel sheet of the present invention with above-mentioned composition and tissue is to have that tensile strength (TS) 440MPa is above, about 780MPa following and to have the r value be the high r value more than 1.2, the cold-rolled steel sheet of good strain-aged hardening characteristics by controlling the ferritic set tissue of parent phase.TS can not be widely used in having on the member of structural member key element less than the steel plate of 440MPa.In addition, in order further to enlarge the scope of application, wish that TS is more than the 500MPa.In addition, if r value less than 1.2 then can not be applicable to large-scale drawing parts.Moreover the preferable range of r value is more than 1.4.

In the present invention, so-called " good strain-aged hardening characteristics " is meant: as described above, after the predeformation of tension strain 5%, 170 ℃ temperature, when keeping under 20 minutes the condition ageing treatment, the deformation stress increasing amount before and after this ageing treatment (is designated as the BH amount; Predeformation stress before yielding stress-ageing treatment after the BH amount=ageing treatment) be more than the 80MPa, and the tensile strength increasing amount before and after the strain aging processing (aforementioned predeformation+aforementioned ageing treatment) (is designated as Δ TS; Tensile strength before tensile strength-predeformation after the Δ TS=ageing treatment) be more than the 40MPa.

The occasion of regulation strain-aged hardening characteristics, prestrain (predeformation) amount becomes the important factor.Inventor's hypothesis is applicable to the distortion pattern of automotive sheet, about the prestrain amount influence of strain-aged hardening characteristics is studied, its result is: the deformation stress in the 1. aforementioned distortion pattern is except profound occasion of drawing processing, and big activation is to be equivalent to 1 strain (tension strain) amount arrangement; 2. in physical unit, this dependent variable that is equivalent to 1 is approximately greater than 5%; 3. the intensity (YS and TS) that has obtained after having found out strength of parts and having handled in the strain aging of prestrain 5% is corresponding well.Based on this knowledge, the predeformation that the present invention handles strain aging is decided to be tension strain 5%.

The baking processing condition of spraying paint in the past adopts 170 ℃ * 20 minutes as standard.Moreover, the steel plate of the present invention of the solid solution N that contains volume is applied strained occasion more than 5%, even more demulcent (low temperature one side) processing also can reach sclerosis, in other words, acquisitive prescription condition more broadly.In addition, in general, in order to strive for hardening capacity, in not because of overaging remollescent limit, keeping under high temperature more is favourable for more time.

Narration particularly, steel plate of the present invention is about 100 ℃ at the become lower limit of significant Heating temperature of predeformation post-hardening.On the other hand, when Heating temperature surpassed 300 ℃, sclerosis culminated, and occurs remollescent trend a little on the contrary, and in addition, becoming of thermal strain and tempering color is remarkable.In addition, about the hold-time, if more than being about about 30 seconds during 200 ℃ of left and right sides of Heating temperature, then can reach sufficient sclerosis substantially.In order to obtain bigger stable sclerosis, the preferred hold-time is more than 60 seconds., when the hold-time surpasses 20 fens kinds, not only can not further be hardened, and production efficiency also significantly reduces, unfavorable aspect practical.

Thus, in the present invention, be decided to be: with 170 ℃, the hold-time of evaluation in 20 minutes as the Heating temperature of the baking processing condition of spraying paint in the past as the ageing treatment condition.Even the baking-type steel plate that sprays paint in the past can not reach under the ageing treatment condition of sufficient hardened low-temperature heat short period of time maintenance, steel plate of the present invention also can stably reach big sclerosis.Moreover the method for heating is restriction especially, removes atmosphere that the stove that adopted by the common baking of spraying paint carries out heats, and for example, the heating of being undertaken by induction heating, non-oxidation flame, laser, plasma etc. etc. can both be used well.

Automobile must be able to be resisted stress-loaded from the complexity of outside with strength of parts, so sheet stock is important in the strength characteristics of little strain regions not only, and also is important in the strength characteristics of big strain regions.The inventor makes the BH amount that will become the raw-material steel plate of the present invention of trolley part for more than the 80MPa according to this point, makes Δ TS amount for more than the 40MPa simultaneously.Moreover more preferably the BH amount is for 100MPa is above, Δ TS is more than the 50MPa.In addition, the Heating temperature by with ageing treatment the time is set in more high temperature one side and/or will be set in longer time one side the hold-time, can more increase BH amount and Δ TS and measure.

In addition, the advantage that steel plate of the present invention has is: do not heat especially after shaping, only at room temperature place about 1 week, can expect that about 40% intensity of complete timeliness increases.

In addition, steel plate of the present invention also possesses the advantage that ageing steel plate was provided with in the past: under the state of processing that is not formed, even timeliness deterioration (phenomenon that YS increases and E1 (unit elongation) reduces) does not take place at room temperature long-time the placement yet.Moreover, in order in the drawing of reality, not produce unfavorable condition, 3 months timeliness at room temperature before drawing must reach: the increasing amount of YS is that 30MPa is following, unit elongation be reduced to below 2%, the answer of elongation at yield point is below 0.2%.

In addition, in the present invention, even do not have any problem in execution plating of the surface of above-mentioned cold-rolled steel sheet of the present invention or hot dip process yet.TS, the BH of equal extent amount, Δ TS amount before these plated film steel plates also demonstrate and plate.As the kind of plated film, electro-galvanizing, galvanizing, alloyed hot-dip zinc-coated, eleetrotinplate, electrodeposited chromium, electronickelling etc. can both be used well.

Manufacture method about the 8th steel plate of the present invention is illustrated.

Steel plate of the present invention is made by implementing following operation successively basically: the plate slab heating back roughing that will have the composition of above-mentioned scope, base laminates, this thin slab is implemented finish rolling, thereby postcooling is finished in finish rolling, the hot-rolled process of making hot-rolled sheet of reeling, this hot-rolled sheet is implemented pickling and the cold rolling cold rolling process of making cold-reduced sheet, this cold-reduced sheet is implemented pack annealing, then carried out the cold-reduced sheet annealing operation of continuous annealing.

The slab that uses in manufacture method of the present invention will prevent the macrosegregation of composition, wishes to adopt the continuous metal cast process manufacturing, but also can adopt ingot casting method, the manufacturing of thin slab casting.In addition, after making slab, except the method always of cool to room temperature for the time being and then heating, do not cool off the dead-beat that just is encased in process furnace and is rolled with hot base state rolling or heat a little after the energy-conservation technology such as direct rolling that directly is rolled also can the use of no problem ground.Particularly in order to guarantee the N of solid solution attitude effectively, dead-beat is rolling to be one of useful technology.

At first, the term restriction reason about hot-rolled process is illustrated.

Slab heating temperature: more than 1000 ℃

As the hot rolled A-stage, in order to ensure essential and solid solution N amount fully, make the solid solution N amount in the goods satisfy target value, slab heating temperature is taken as more than 1000 ℃ to well.Moreover, because along with the increase loss of oxidation weight increases, so wish to be taken as below 1280 ℃.

Jia Re slab is by the roughing base that laminates under these conditions.Moreover the condition of roughing needn't special stipulation, as long as according to ordinary method., consider, wish to carry out with the short period of time as far as possible from the viewpoint of guaranteeing solid solution N amount.Then the planished sheet base is made hot-rolled sheet.

Moreover, in the present invention, between roughing and finish rolling, wish that the thin slab that front and back are adjacent is engaged with each other, continuous rolling.Use pressure welding method, method of laser welding, electron beam welding connection etc. for well as engagement means.

By continuous rolling, the so-called rolling non-constant part of the front-end and back-end of coiled material (processed material) becomes and does not have, and stable hot-rolled condition spreads all over coiled material (processed material) total length and overall with becomes possibility.This also is extremely effective not only to hot-rolled steel sheet to cross-sectional shape and the size of improving cold-rolled steel sheet.In addition, rolling after, cooling the time also can give tension force on hot run table, so can keep the steel plate shape well.

In addition,, the coiled material front end is stably passed through, in the unit of each common thin slab is rolling, can use the out of use lubrication and rolling of problem because of sheet material trafficability characteristic and engaging-in property for by carrying out tandem rolling.Can reduce rolling load in view of the above, also can reduce the surface pressure of roll simultaneously, can prolong the life-span of roll.

In addition, in the present invention, finishing mill between roughing and finish rolling advances base one side, use add the hot thin slab lateral ends thin slab edges of boards well heater, add any one party or two sides in the thin slab well heater of hot thin slab longitudinal end, make the thin slab width and longitudinally uniformity of temperature profile for well.In view of the above, the material that can further reduce in the steel plate is discrete.Thin slab edges of boards well heater, thin slab well heater are induction heating mode for well.

Use wishes at first to adopt the temperature head of thin slab edges of boards well heater compensation width in proper order.The heat that adds of this moment also is based on steel and forms, but the width temperature distribution scope that finish rolling goes out material one side be set at about below 20 ℃ for well.Then utilize the temperature head of thin slab well heater compensating length direction.This moment add heat set for the longitudinal end temperature than central area temperature high approximately about 20 ℃ for good.

Finish rolling goes out the material temperature: more than 800 ℃

In order to obtain evenly fine hot rolling motherboard tissue, finish rolling goes out material temperature FDT and is taken as more than 800 ℃.When FDT was lower than 800 ℃, the tissue of steel plate became inhomogeneous, and partly the residual process tissue can not be eliminated and left behind through the ununiformity of organizing after the cold rolled annealed operation.Therefore, when to avoid worked structure residual, when adopting high coiling temperature, produce coarse grain, same unfavorable condition takes place.In addition, be high temperature by making the coiling temperature, the remarkable reduction of solid solution N amount takes place, therefore be difficult to obtain tensile strength as more than the purpose 440MPa.Because this situation, finish rolling goes out material temperature FDT and is taken as 800 ℃.In order further to improve mechanical properties, wish that making FDT is more than 820 ℃.The not special stipulation of the upper limit of FDT, but when exceedingly high, scale thing defective etc. become remarkable.Moreover FDT is taken as approximately about 1000 ℃ for well.

Moreover the cooling after the finish rolling does not especially strictly limit, but is wishing to be following condition aspect the material homogeneity of the portraitlandscape of steel plate.That is, the present invention wishes that after finish rolling is finished (in 0.5 second) begins to cool down immediately, and making the average cooling rate in the cooling is more than 40 ℃/second.By satisfying this condition, the high-temperature zone chilling that AlN can be separated out can be guaranteed the N of solid solution attitude effectively.When this cooling time opening or speed of cooling do not satisfy above-mentioned condition, grain growth excessively carries out, and is difficult to reach the refinement of crystal grain, and exists because of the AlN due to the rolling strain energy that imports and separate out by promoted tendency, might lack solid solution N, uneven in a organized way tendency.Moreover, consider that from the inhomogeneity viewpoint of guaranteeing the material shape speed of cooling is suppressed at below 300 ℃/second to well.

Coiling temperature: below 800 ℃

Along with the reduction of coiling temperature CT, there is the trend that increases in armor plate strength.More than target tensile strength TS440MPa, CT is taken as below 800 ℃ to well.Moreover when 200 ℃ of CT less thaies, the steel plate shape is irregular easily, in the actually operating, produces the dangerous high of unfavorable condition, demonstrates the tendency that the material homogeneity reduces.Therefore, wish that CT is taken as more than 200 ℃.Moreover, more requiring the inhomogeneity occasion of material, CT is taken as more than 300 ℃ to well.More preferably more than 350 ℃.In addition, in the present invention, when finish rolling,, also can be lubricated rolling in order to reduce hot rolling load.Rolling by being lubricated, the shape material effect of uniform more that makes hot-rolled sheet is arranged.Moreover, the frictional coefficient during lubrication and rolling in 0.25～0.10 scope for well.In addition, the rolling and continuous rolling by combined lubrication, the hot rolled operation is stable.

The hot-rolled sheet of having implemented above-mentioned hot-rolled process is implemented pickling and cold rolling then by cold rolling process, makes cold-reduced sheet.

The condition of pickling gets final product with generally well-known condition, does not limit especially.Moreover, in the scale thing occasion as thin as a wafer of hot-rolled sheet, also can not implement pickling and directly carry out cold rolling.

In addition, cooling conditions gets final product with generally well-known condition, does not limit especially.Moreover, consider that from the viewpoint of guaranteeing homogeneity of structure cold draft is taken as more than 40% to well.Below illustrated about the term restriction reason of cold rolling process.

Cold-reduced sheet is then implemented the cold-reduced sheet annealing operation that is made of pack annealing, continuous annealing.

The pack annealing temperature: more than the recrystallization temperature～below 800 ℃

In the present invention, cold-reduced sheet is implemented pack annealing, control becomes the set tissue of the ferritic phase of matrix.By controlling the set tissue of this ferritic phase, can seek the high r value of sheet.By this pack annealing, in sheet, form easily and realize high r value and desirable (111) set tissue.

When pack annealing temperature during less than recrystallization temperature, can not finish recrystallize, can not adjust the set tissue of ferritic phase, can not seek high r value.On the other hand, during pack annealing, becoming significantly of Surface Defects in Steel Plate can not reach the purpose at initial stage under surpassing 800 ℃ temperature.Moreover pack annealing is based on nitrogen, carries out to good containing under the annealing atmosphere of 3～5% hydrogen.Under this occasion, the heating speed of cooling adopts common pack annealing condition to get final product, and is approximately about 30 ℃/hour.In addition, be 100% hydrogen by making annealing atmosphere gas, can adopt and heat speed of cooling faster.

Continuous annealing temperature: Ac ₁More than the transformation temperature～(Ac ₃Transformation temperature-20 ℃) below

As the not enough Ac of continuous annealing temperature ₁During transformation temperature, can not form martensitic phase after the annealing, on the other hand, when surpassing (Ac ₃Transformation temperature-20 ℃) time, the desirable set tissue that forms in pack annealing is lost because of phase transformation, so can not obtain having the sheet of high r value.Therefore, continuous annealing temperature is taken as Ac ₁More than the transformation temperature～(Ac ₃Transformation temperature-20 ℃) following for well.In addition, the hold-time of continuous annealing time from production efficiency, thinning microstructure, guarantee that the viewpoint of solid solution N amount considers, short in as much as possible well.On the other hand, consider that the hold-time is for well more than 10 seconds from the viewpoint of the stability of operation.In addition, from thinning microstructure with guarantee that the viewpoint of solid solution N amount considers, be taken as below 120 seconds to well.Moreover, consider from the viewpoint of the stabilization of material, be taken as more than 20 seconds better.

Cooling after the continuous annealing: be cooled to humidity province below 500 ℃ with 10～300 ℃/second speed of cooling

Cooling after the soaking in the continuous annealing from thinning microstructure, form martensitic phase, guarantee the viewpoint of solid solution N amount considers it is important.In the present invention, be cooled to humidity province below 500 ℃ continuously with the speed of cooling more than 10 ℃/second at least.When 10 ℃/second of speed of cooling less thaies, can not obtain the martensite volume of necessary amounts, even and fine tissue and the solid solution N of q.s.On the other hand, when speed of cooling surpassed 300 ℃/second, oversaturated solid solution C amount significantly increased, so steel plate reduces in the homogeneity of horizontal material.When the cooling under 10～300 ℃/second speed of cooling after the continuous annealing stops temperature above 500 ℃, can not reach the refinement of tissue.

The overaging treatment condition: continue with the cooling after the continuous annealing, the humidity province residence time that stops below the temperature, more than 350 ℃ in this refrigerative cooling is more than 20 seconds

Stop to continue with the cooling after the soaking of continuous annealing, stopping humidity province below the temperature, more than 350 ℃ in cooling, to carry out the residence time be that overaging more than 20 seconds is handled also passable.Handle by carrying out overaging, can under the state of keeping solid solution N amount, optionally reduce solid solution C amount.When 350 ℃ of retention temperature district less thaies, reducing solid solution C needs for a long time, cause that productivity reduces, and therefore is taken as humidity province more than 350 ℃ for well.

Be detained more than 20 seconds by the humidity province that stops in cooling below the temperature, more than 350 ℃, can reduce solid solution C amount, reach the more non-ageing at room temperature of height.By making the residence time longer, be expected further improvement, but its effect is tending towards saturated when the about 120 seconds left and right sides, so be taken as below 120 seconds to well the residence time.

In order to obtain big strain-age hardening amount, it is favourable that solid solution C and solid solution N utilize, but when utilizing solid solution C, becomes significantly in the timeliness deterioration of room temperature, and the suitable position of steel plate is restricted.Therefore, in order to make strain-age hardening shaped steel plate, on the basis of the solid solution N that guarantees fully to measure, carry out overaging and be treated to widely-used property.

Moreover, be manufactured on high strength cold rolled steel plate of the present invention surface and have the occasion of hot-dip coated high strength cold rolled steel plate, carry out continuous annealing after on the continuous hot-dipping production line, following pack annealing closely, continue with the cooling after the continuous annealing, carry out galvanizing or carry out Alloying Treatment again, also can make hot-dip galvanized steel sheet.

Skin-pass or leveling processing: unit elongation 0.2～15%

In the present invention, continue,, also can implement the processing of skin-pass or leveling for the purpose of correcting shape, adjustment smooth finish with cold rolled annealed operation.When the unit elongation of skin-pass or leveling processing adds up to quantity not sufficient 0.2%, can not reach the desired purpose of correcting shape, adjusting smooth finish.On the other hand, when surpassing 15%, cause significant ductility to reduce.Moreover, for skin-pass and leveling processing, its form processing difference, both do not have big difference but confirmed its effect.Even skin-pass, leveling processing also are effective after coating film treatment.

Below for reference, the molding condition when this invention steel plate being used for the occasion of shaping such as drawing processing with and subsequent intensity rising heat-treat condition illustrated.The steel plate of this invention for example is used to draw the occasion of the punch process of processing etc., and the strain that imports by punch process is percentum～tens percent.Differently strained amount according to molded component changes, but inner panel in automotive field and structure unit can import the strain about 5～10%.

Then, these molded components are implemented thermal treatments such as the baking processing of spraying paint, but this invention steel plate can improve molding intensity effectively after thermal treatment.Moreover, in this invention,, produce the tension test sheet of No. 5 sizes of JIS along rolling direction as method at this baking hardenability of laboratory evaluation, utilize tensile testing machine to give 10% tension strain, apply thermal treatment then after, implement tension test once more.Particularly estimate the occasion of the characteristic after the thermal treatment of cold zone, heat-treat condition is decided to be 120 ℃, 20 minutes.This test evaluation follows the characteristic of having carried out the parts after heat treated the finishing after the drawing closely.

That is, in this invention, so poor (Δ TS) that gives the tensile strength of tensile strength after tension strain one thermal treatment and goods defined as intensity rising heat treatment capacity.

Usually, in order to improve the intensity ascending amount of molding, the thermal treatment temp after the big or processing of the dependent variable that imports by shaping is high for well.

, this invention steel plate is above-mentioned about 5～10% occasion in the dependent variable that gives, even shaping postheat treatment temperature is lower than in the past, promptly thermal treatment temp also can be sought enough intensity and rise below 200 ℃.Though so, during 120 ℃ of thermal treatment temp less thaies, can not obtain ascending effect on the full intensity answering under the situation of step-down.On the other hand, the thermal treatment temp after being shaped is when surpassing 350 ℃ temperature, will soften.So the thermal treatment temp after the shaping is taken as about 120～350 ℃ to well.

Moreover, as heating means, can use methods such as hot blast heating, infra-red furnace heating, heating bath thermal treatment, energising heating, ratio-frequency heating, do not stipulate especially.In addition, also can be only optionally to heat the part that intensity is risen.

Embodiment

In following embodiment, solid solution N amount, microstructure, tensile properties, r pH-value determination pH, strain-aged hardening characteristics, aging characteristic have been investigated.Investigation method is as follows.

(1) solid solution N amount

The solid solution N amount total N content from the steel of being obtained by chemical analysis deducts separates out the N amount and obtains.Separating out the N amount herein, is to adopt the analytical method of having used above-mentioned constant potential electrolytic process to obtain.

(2) microstructure

Produce test film from each cold rolled annealed plate, use opticmicroscope or scanning electron microscope pair to take microstructure, use visual resolver to obtain and ferriticly organize the kind of mark and the 2nd phase and organize mark with the vertical cross section of rolling direction (C cross section).

(3) size of microcrystal

In the present invention, as size of microcrystal is to adopt from the section structure photo to utilize value that the planimetry of ASTM regulation obtains and utilize nominal diameter that the cutting-off method of ASTM regulation obtains (for example from the section structure photo, with reference to Mei Ben etc.: thermal treatment, 24 (1984), 334) the some big value among.

(4) tensile properties

Produce No. 5 test films of JIS from each cold rolled annealed plate along rolling direction, according to the regulation of JIS Z 2241 with rate of straining: 3 * 10 ^-3Yielding stress YS, tensile strength TS, unit elongation E1 are obtained in/second enforcement tension test.

(5) strain-aged hardening characteristics

Produce No. 5 test films of JIS from each cold rolled annealed plate along rolling direction, as predeformation in this stretching prestrain of bestowing 5%, then implement 170 ℃ * 20 minutes be equivalent to spray paint after the thermal treatment of baking processing, with rate of straining 3 * 10 ^-3/ second implement tension test, obtain the tensile properties (yielding stress YSBH, tensile strength TSBH) after the predeformation-baking processing of spraying paint, calculate BH amount=YSBH-YS5%, Δ TS=TSBH-TS.Moreover YS5% is the deformation stress during with sheet predeformation 5%, and YSBH, TSBH are yielding stress, the tensile strengths after the predeformation-baking processing of spraying paint, and TS is the tensile strength of sheet.

(6) r pH-value determination pH

From the rolling direction (L direction) of each cold rolled annealed plate, be 45 ° direction (D direction), be 90 ° direction (C direction) with rolling direction and produce No. 5 test films of JIS with rolling direction.Obtain the transvrsal strain and the strain of thickness of slab direction of each test film when these test films are applied 5% uniaxial tensile strain, by transvrsal strain and thickness of slab direction strained ratio as the definition of r value

r＝ln(w/w ₀)/In(t/t ₀)

(wherein, w ₀, t ₀Be the width and the thickness of slab of the test film before testing, w, t are the width and the thickness of slab of the test film after testing.) obtain the r value of all directions, pass through following formula

r _{On average}=(r _L+ 2r _D+ r _CIt is average that average r value r is obtained in)/4.Wherein, r _LBe the r value of rolling direction (L direction), r _DFor being the r value of 45 ° direction (D direction), r with rolling direction (L direction) _CFor being the r value of 90 ° direction (C direction) with rolling direction.Moreover, in order to improve the precision of experiment, be assumed to be given volume, calculate by the variation of tension strain and transvrsal strain.

(7) aging characteristic

Produce No. 5 test films of JIS from each cold rolled annealed plate, this test film is applied 50 ℃ * 200 hours ageing treatment after, implement tension test, obtain yield extension rate variance Δ Y-E1 before and after the ageing treatment by the result of gained, estimate the aging characteristic of normal temperature.If Δ Y-E1 is 0, then as the non-ageing characteristic good of anti-room temperature ageing that is evaluated as.

(8) tensile strength after the shaping-thermal treatment

Tensile strength after the shaping-thermal treatment is to produce No. 5 test films of JIS from the sheet upper edge in the system direction, after giving 10% prestrain, in 120 ℃ and the conduct carried out be equivalent to spray paint 170 ℃ of thermal treatments of implementing 20 minutes down of thermal treatment temp of baking in the past, measure tensile strength and obtain.

(9) the reduction amount of the breaking elongation due to the room temperature ageing (Δ E1)

The promotion of room temperature ageing that the reduction amount of the breaking elongation due to the room temperature ageing (Δ E1) is the breaking elongation that will produce No. 5 test films of JIS from sheet upper edge rolling direction and measure with the execution of having used in addition No. 5 test films of producing along rolling direction of JIS is handled the differing from of breaking elongation of (100 ℃ kept 8 hours) back mensuration and is obtained.

Embodiment 1

The plate slab that becomes to be grouped into shown in the table 1 is made the hot-rolled sheet that thickness of slab is 3.5mm under condition shown in the table 2, after then making the cold-reduced sheet that thickness of slab is 0.7mm, on continuous annealing line or continuous annealing-alloyed hot-dip zinc-coated line, implement recrystallization annealing, implement alloyed hot-dip zinc-coated processing again, implement draft then: 1.0% skin-pass, thus making cold-rolled steel sheet and with average coating single side amount: 45g/m2 carries out the alloyed hot-dip galvanized steel plate of two sides plated film.Moreover it is not enough Ar3 transformation temperature that No.3 in the table 2,8 hot rolling machine temperature, in addition more than the Ar3 transformation temperature.

Investigate about the cold-rolled steel sheet that obtains like this and the tensile strength of alloyed hot-dip galvanized steel plate and the variation of the tensile strength after r value and the shaping-thermal treatment, the results are shown in table 3.

As shown in Table 3, compare with comparative example, all can obtain high r value and good strain-aged hardening characteristics by cold-rolled steel sheet and alloyed hot-dip galvanized steel plate that this invention obtains.In addition, particularly be fit among the example, size of microcrystal is that the reduction amount of the unit elongation due to following its room temperature ageing of steel plate of 20 μ m is represented with Δ E1, also diminishes to below 2.0%.

Embodiment 2

Use the slab of the grade of steel B of table 1 record, as the slab heating temperature of creating conditions identical: 1100 ℃, hot finishing temperature: after 900 ℃ of following hot rollings, in the coiling temperature: be wound into coiled material under 550 ℃ with the No.2 of table 2.With draft: behind 80% cold rolling this coiled material, under 840 ℃, carry out recrystallization annealing.The article characteristic of the cold-rolled steel sheet of gained is tensile strength TS=365Mpa, r value=1.7.Produce No. 5 test films of J1S from this cold-reduced sheet upper edge rolling direction, utilize tensile testing machine to give 10% tension strain after, implement thermal treatment down in the heat-treat condition shown in the table 4 (temperature, time), carry out tension test once more.Table 4 has been charged to the tensile strength ascending amount (Δ TS) from the tensile strength (TS=365MPa) that gives the goods before the strain simultaneously.

According to shown in the table 4, thermal treatment temp is high more, heat treatment time is long more, then the ascending amount of intensity is big more, even be as short as 2 minutes but invention steel plate thermal treatment temp is low to moderate 120 ℃ and hold-time, the thermal treatment of low temperature short period of time also can obtain the sufficient tensile strength ascending amount (during thermal treatment in 20 minutes more than 85%) of 82MPa, even also can obtain good strain-aged hardening characteristics.Moreover in structural member of automobile etc., in order to obtain ascending effect on the stable intensity, heat-treating under common temperature, time does not have any problem yet.Show in addition: this cold-rolled steel sheet is implemented galvanizing and heating Alloying Treatment, for the alloyed hot-dip galvanized steel plate of gained, also can obtain the result same with table 4.

Embodiment 3

Plate slab hot rolling under condition shown in the table 7 of forming shown in the table 6 is made the hot-rolled sheet of thickness of slab 3.5mm.Cold rolling these hot-rolled sheets under condition shown in the table 7 are made the cold-reduced sheet of thickness of slab 0.7mm, with these cold-reduced sheet recrystallization annealing, a part are wherein being implemented galvanizing or alloyed hot-dip zinc-coated under the condition shown in this table again under condition shown in this table.Sheet investigation solid solution N amount, microstructure, tensile properties, strain-aged hardening characteristics about gained.

The results are shown in table 8.By this table as can be known, steel plate constructed in accordance, all satisfy TS * value 〉=750MPa (when the time with the compound interpolation more than a kind or 2 kinds of B and Nb, Ti, V, TS * r value 〉=850MPa), BH 〉=80MPa, Δ TS 〉=40MPa further, but, do not reach level of the present invention more than a kind in this 3 specific character to comparative example.

Embodiment 4

Illustrated about embodiments of the invention below.

With the molten steel of forming shown in the converter smelting table 9, make steel billet with continuous metal cast process.These steel billets of heating carry out the roughing base that laminates under condition shown in the table 10, and then, the hot-rolled process of the finish rolling by condition shown in the execution table 10 is made hot-rolled sheet.Moreover, under the mimic condition, use processing phase transformation determinator (Fuji's electric wave industrial machinery corporate system) to measure the Ar3 transformation temperature, the hot finishing condition is shown in table 10.

By these hot-rolled sheets being made cold-reduced sheet by the cold rolling cold rolling process that constitutes of condition shown in pickling and the table 10.Then, under condition shown in the table 10, these cold-reduced sheets are carried out continuous annealing.A part is wherein implemented skin-pass after cold rolled annealed operation.

About the cold rolled annealed plate of gained, investigation solid solution N amount, microstructure, tensile properties, r pH-value determination pH, strain-aged hardening characteristics, aging characteristic.

Moreover, the surface of steel plate of No.4, No.10 is implemented galvanizing, form the plated film steel plate, similarly estimate various characteristics.

These the results are shown in table 11.

For example of the present invention, all demonstrate good ductility and extra high BH amount, Δ TS, be non-ageing good anti-room temperature ageing when having good strain-aged hardening characteristics, average r value and be high r value more than 1.2, room temperature ageing.Moreover, the surface of steel plate of No.4, No.10 is implemented the characteristic of the plated film steel plate of galvanizing gained, because the transverse contraction of coating is restrained, so with the cold-rolled steel sheet ratio, average r value reduces by 0.2, unit elongation E1 reduces about 1%, but the characteristic before strain-age hardening, anti-room temperature ageing and the plating does not change than basic.On the contrary, the comparative example outside the scope of the invention, its deteriorated ductility or BH measure, Δ TS is few or the timeliness deterioration is remarkable, can not possess the target complete characteristic, can not say so to have the steel plate of abundant characteristic.

The C of steel plate No.11, Al, N, N/Al depart from the scope of the invention, therefore, and r value, BH amount, Δ TS, anti-room temperature ageing reduction.In addition, B, the Nb of steel plate No.12 depart from the scope of the invention, and the acicular ferrite amount is lower, has departed from the scope of the invention, therefore, and BH amount, Δ TS, anti-room temperature ageing reduction.

The B of steel plate No.13 departs from OK range of the present invention, and the acicular ferrite amount is lower, has departed from the scope of the invention, therefore, and r value, BH amount, Δ TS, anti-room temperature ageing reduction.In addition, the Nb of steel plate No.14 departs from the scope of the invention, and solid solution N amount is lower, has departed from the scope of the invention, and therefore, strain-aged hardening characteristics reduces.

The N of steel plate No.15 has departed from OK range of the present invention, and solid solution N is few, and strain-aged hardening characteristics reduces.The hot-rolled condition of steel plate No.17～No.20, cold-reduced sheet annealing conditions depart from OK range, and microstructure is outside the scope of the invention, and BH amount, Δ TS reduce, and strain-aged hardening characteristics reduces, anti-room temperature ageing deterioration.

Embodiment 5

Adopt method similarly to Example 4 that the steel of forming shown in the table 12 is made slab, this slab of heating under condition shown in the table 13 carries out roughing and forms the thick thin slab of 25mm, and then the hot-rolled process of the finish rolling by condition shown in the execution table 13 is made hot-rolled sheet.Moreover, after roughing, advance base one side in finish rolling and be engaged with each other with the fusion pressure welding method thin slab that front and back are adjacent, carry out continuous rolling.In addition, use thin slab edges of boards well heater, the width end of thin slab heater heats thin slab, the length direction end of induction heating mode, regulate the temperature of thin slab.

By these hot-rolled sheets being made the thick cold-reduced sheet of 1.6mm by the cold rolling cold rolling process that constitutes of condition shown in pickling and the table 13.Then, under the conditions shown in Table 13 these cold-reduced sheets are carried out continuous annealing.

About the cold rolled annealed plate of gained, investigate solid solution N amount, microstructure, tensile properties, r pH-value determination pH, strain-aged hardening characteristics with embodiment 4 the samely.In addition, about the width of each cold rolled annealed plate and vertically, at each 10 positions investigation tensile properties, investigation yield strength, tensile strength, unit elongation discrete.

These the results are shown in table 14.

Example of the present invention all has good strain-aged hardening characteristics and high r value, although the fluctuation of creating conditions also stably demonstrates extra high BH amount, Δ TS, average r value.Confirm in addition: in example of the present invention, continuous rolling and thin slab are vertical by implementing, the temperature adjustment of width, and the thickness of slab precision of goods steel plate and shape improve, and material is discrete to be reduced to 1/2.In addition, make that the unit elongation of skin-pass changes to 0.5～2%, the unit elongation of leveling changes to 0～1%, but strain-aged hardening characteristics does not reduce.

Embodiment 6

Illustrated about embodiments of the invention below.

With the molten steel of forming shown in the converter smelting table 15, adopt continuous metal cast process to make plate slab.Heating (a part of hot base is packed into) these plate slabs carry out the roughing base that laminates under condition shown in the table 16, and then the hot-rolled process of the finish rolling by condition shown in the execution table 16 is made hot-rolled sheet.Moreover a part of thin slab adopts the fusion pressure welding method thin slab that front and back are adjacent to be engaged with each other, and carries out continuous rolling.

By these hot-rolled sheets being made cold-reduced sheet by the cold rolling cold rolling process that constitutes of condition shown in pickling and the table 16.Then, the continuous annealing of under condition shown in the table 16, these cold-rolled steel sheets being carried out pack annealing and continuing with pack annealing.Wherein a part is implemented skin-pass after cold rolled annealed operation.Moreover the annealed situation of not casing has also been implemented.The annealing temperature of pack annealing all is taken as more than the recrystallization temperature.

About the cold rolled annealed plate of gained, solid solution N amount, microstructure, tensile properties, r pH-value determination pH, strain-aged hardening characteristics, aging characteristic have been investigated.

Moreover after the continuous annealing in table, the surface of steel plate to No.17, No.18 on production line is implemented galvanizing, makes the plated film steel plate, similarly estimates various characteristics.

These be the results are shown in table 17.

In example of the present invention, all demonstrate good ductility and especially high BH amount, Δ TS, the high r value, the normal temperature that have good strain-aged hardening characteristics, average r value and be more than 1.2 are non-ageing.Moreover, the characteristic of the hot-dip galvanized steel sheet of steel plate No.17, the No.18 shown in the table 17, similarly with the characteristic of the cold-rolled steel sheet of continuous annealing than there not being difference substantially.On the contrary, depart from the comparative example of the scope of the invention, its deteriorated ductility or BH measure, Δ TS is few or the timeliness deterioration is remarkable, can not possess all target properties, can not say so to have the steel plate of abundant characteristic.

The C of steel plate No.11, N amount departs from the scope of the invention, and solid solution N measures, martensite volume is lower, has departed from the scope of the invention, so BH measures, Δ TS reduces, and Δ Y-E1 increases.In addition, the Al of steel plate No.12, N/Al, N have departed from the scope of the invention, and solid solution N amount is lower, departs from the scope of the invention, and ferritic average crystal grain particle diameter is big, departs from the scope of the invention, and therefore, BH amount, Δ TS reduce, and Δ Y-E1 increases.

The slab heating temperature of steel plate No.13 and FDT depart from OK range of the present invention, and solid solution N measures, martensite volume is lower, has departed from the scope of the invention, ferritic average crystal grain particle diameter is big, has departed from the scope of the invention, therefore, r value, BH amount, Δ TS reduce, in addition, and the coiling temperature departure scope of the invention after the hot rolling of steel plate No.14, solid solution N amount is lower, departed from the scope of the invention, ferritic average crystal grain footpath is big, has departed from the scope of the invention, therefore, r value, BH amount, Δ TS reduce.

The continuous annealing temperature of steel plate No.15 breaks away from OK range of the present invention, can not generate martensite, and ferritic average crystal grain particle diameter is big, departs from the scope of the invention, and therefore, BH amount, Δ TS reduce, and Δ Y-E1 increases.In addition, steel plate No.16 does not implement pack annealing, and desirable set is organized undeveloped, and therefore particularly the r value reduces.In addition, ferritic median size, martensitic area occupation ratio also depart from the scope of the invention.

Embodiment 7

Adopt method similarly to Example 1 that the steel of forming shown in the table 18 is made slab, this slab of heating carries out roughing and makes the thick thin slab of 30mm under condition shown in the table 19, and then the hot-rolled process of the finish rolling by condition shown in the execution table 19 is made hot-rolled sheet.Moreover wherein a part is advanced base one side in finish rolling and is adopted the fusion pressure welding method thin slab that front and back are adjacent to be engaged with each other after roughing, carries out continuous rolling.In addition, use the thin slab edges of boards well heater of induction heating mode, width end, the longitudinal end of thin slab heater heats thin slab, regulate the temperature of thin slab.

By these hot-rolled sheets being made the thick cold-reduced sheet of 1.6mm by the cold rolling cold rolling process that constitutes of condition shown in pickling and the table 19.Then, under condition shown in the table 19, these cold-reduced sheets are carried out pack annealing, then used the continuous annealing of continuous annealing furnace.Moreover the annealing temperature of pack annealing all is taken as more than the recrystallization temperature.

About the cold rolled annealed plate of gained, solid solution N amount, microstructure, tensile properties, r pH-value determination pH, strain-aged hardening characteristics have been investigated with embodiment 1 the samely.In addition, about the width of each cold rolled annealed plate and vertically, at each 10 positions investigation tensile properties, investigation yield strength, tensile strength, unit elongation discrete.Moreover, poor, for example δ YS=(maximum value of YS)-(minimum value of the YS) expression of maximum value in all sites that is used in mensuration that disperses and minimum value.It the results are shown in table 20.

Example of the present invention all has good strain-aged hardening characteristics and high r value, although create conditions fluctuation, also stably demonstrates especially high BH amount, Δ TS, average r value.Confirm in addition: in example of the present invention, continuous rolling and thin slab are vertical by implementing, the temperature adjustment of width, and the thickness of slab precision of goods steel plate and shape improve, and material is discrete to be reduced.

Utilize possibility on the industry

According to the present invention, can obtain when drawing, guaranteeing good deep-draw ductility, simultaneously by drawing-thermal treatment, the cold-rolled steel sheet that TS increases widely.And can obtain following good effect: but adopt this cold-rolled steel sheet industrialness ground to make electrogalvanizing steel plate, hot-dip galvanized steel sheet, alloyed hot-dip galvanized steel plate.Table 1

Steel	Become to be grouped into (quality %)									(1) ' formula *	(2) ' formula **	Remarks
													????C	????N	????Si	????Mn	????B	????Al	????Nb	????P	????S
	??A	??0.0009	??0.011	??0.01	??0.12	??0.0009	??0.010	??0.016	??0.009													??0.005	????0.0023	?-0.0001	Be fit to example
??B										??0.0020	??0.015	??0.01	??0.11	??0.0011	??0.012	??0.035	??0.015	??0.006	????0.0021	?-0.0003	????″
	??C	??0.0005	??0.009	??0.01	??0.09	??0.0005	??0.009	??0.010	??0.011													??0.005	????0.0022	?-0.0001	????″
??D										??0.0020	??0.021	??0.01	??0.50	??0.0015	??0.020	??0.035	??0.030	??0.004	????0.0035	?-0.0003	????″
	??E	??0.0003	??0.010	??0.50	??0.12	??0.0006	??0.011	??0.099	??0.045													??0.010	????0.0022	?-0.0003	????″
??F										??0.0011	??0.030	??0.80	??0.80	??0.0011	??0.028	??0.025	??0.009	??0.005	????0.0103	?-0.0005	????″
	??G	??0.0011	??0.018	??0.70	??0.12	??0.0008	??0.012	??0.018	??0.008													??0.005	????0.0080	?-0.0001	????″
??H										??0.0005	??0.020	??0.35	??0.11	??0.0014	??0.020	??0.025	??0.007	??0.005	????0.0041	?-0.0011	????″
	??I	??0.0098	? 0.002	??0.01	??0.12	??0.0007	? 0.038	??0.055	??0.009													??0.005	???-0.0269	??0.0027	Comparative example
??J										??0.0022	? 0.001	??0.50	??0.12	??0.0008	??0.012	? 0.001	??0.008	??0.005	???-0.0064	??0.0021	????″
	??K	??0.0260	? 0.003	??0.02	??0.25	? 0.0001	? 0.035	? 0.001	??0.013													??0.007	???-0.0154	??0.0259	????″
??L										??0.0027	??0.011	??0.01	??0.12	??0.0007	??0.014	? 0.001	??0.009	??0.005	????0.0027	??0.0026	????″

* (1) ' formula: N%-(14/93Nb%+14/27Al%+14/11B%) (being suitable scope of the present invention more than 0.0015)

* (2) ' formula: C%-(0.512/93Nb%) (being suitable scope of the present invention below 0) table 2

??No.	Steel	Hot-rolled condition				The cold process conditions of prolonging				Remarks
											Slab heating temperature (℃)	Finish rolling finish temperature (℃)	Cooling conditions after the finish rolling (s, ℃/s)	The coiling temperature (℃)	Cold rolling draft (%)	Heat-up rate (℃/s)	The recrystallization annealing temperature (℃)	Have or not alloyed hot-dip zinc-coated processing
		??1	??A	????1150	????920	??0.39，58	??600	????80	????15										????840	Have	Be fit to example
??2	??B									????1100	????900	??0.32，53	??550	????80	????15	????840	????″	????″
		??3	??C	????1130	????650 *	??0.25，15	??600	????80	????15										????840	Do not have	????″
??4	??D									????1110	????900	??0.35，59	??400	????80	????15	????840	????″	????″
		??5	??E	????1160	????920	??0.28，70	??650	????80	????15										????840	Have	????″
??6	??F									????1150	????910	??0.39，65	??550	????80	????15	????840	????″	????″
		??7	??G	????1150	????900	??0.36，58	??500	????80	????15										????840	Do not have	????″
??8	??H									????1000	????680 *	??0.26，20	??500	????80	????15	????840	????″	????″
		??9	??A	????1150	????920	??1.13，10	??600	????80	????25										????840	Have	????″
??10	??E									????1160	????920	??0.67，15	??650	????80	????25	????840	????″	????″
		??11	? I	????1140	????920	??0.35，57	??650	????80	????15										????840	Have	Comparative example
??12	? J									????1000	????900	??0.68，7	??550	????80	????15	????840	????″	????″
		??13	? K	????1150	????880	??0.38，61	??500	????80	????15										????840	Do not have	????″
??14	? L									????1000	????920	??1.02，9	??600	????80	????15	??? 940	????″	????″

^*It is not enough Ar that temperature is finished in finish rolling ₃Transformation temperature.Cooling conditions after the finish rolling represent to cool off the time opening (s) and speed of cooling (℃/s).Table 3

??No.	Steel	Article characteristic				Tensile strength after the shaping-thermal treatment changes				Remarks
											Tensile strength T.S. (MPa)	The r value	Size of microcrystal (μ m)	???ΔE1 ???(％)	T.S. (MPa) after 120 ℃ of thermal treatment	Δ T.S. (MPa) after 120 ℃ of thermal treatment	T.S. (MPa) after 170 ℃ of thermal treatment	Δ T.S. (MPa) after 170 ℃ of thermal treatment
		??1	??A	????360	??1.8	????18	????1.6	????435	????75										????455	????95	Be fit to example
??2	??B									????365	??1.7	????12	????1.2	????460	????95	????470	????105	????″
		??3	??C	????355	??2.3	????19	????1.8	????420	????65										????440	????85	????″
??4	??D									????390	??1.9	????14	????1.3	????480	????90	????490	????100	????″
		??5	??E	????430	??1.8	????18	????1.7	????520	????90										????530	????100	????″
??6	??F									????460	??1.6	????18	????1.7	????575	????115	????595	????135	????″
		??7	??G	????430	??1.8	????13	????1.4	????540	????110										????555	????125	????″
??8	??H									????390	??2.1	????19	????1.7	????490	????100	????510	????120	????″
		??9	??A	????352	??1.9	????22	????2.4	????414	????62										????440	????88	????″
??10	??E									????417	??1.9	????23	????2.7	????489	????72	????503	????86	????″
		??11	? I	????370	??1.9	????18	????3.2	????420	????50										????450	????80	Comparative example
??12	? J									????400	??1.6	????22	????2.4	????435	????35	????460	????60	????″
		??13	? K	????360	??1.1	????26	????3.1	????390	????30										????415	????55	????″
??14	? L									????360	??1.2	????25	????4.2	????414	????54	????445	????85	????″

Table 4 Table 5

????Al ????％	?????N/Al	TS * r value MPa	????ΔTS ?????MPa
				????0.020	????0.75	????775	????58
????0.036	????0.42	????762	????55
				????0.049	????0.31	????753	????42
????0.072	????0.21	????720	????25
				????0.080	????0.19	????719	????19

Table 6

Steel	??C ??％	??Si ??％	??Mn ??％	??P ??％	??S ??％	??N ??％	??Al ??％	??Nb ??％	??Ti ??％	??V ??％	??B ??％	??N/(Al+Nb+ ???Ti+V+B)*	??Ar 3??℃
														??A	0.0013	??0.01	??0.15	?0.009	?0.005	?0.0135	?0.011	?---	?---	?---	?---	????1.23	??884
??B	0.0012	??0.50	??0.50	?0.011	?0.004	?0.0175	?0.010	?0.010	?---	?---	?0.0010	????0.83	??888
														??C	0.0008	??0.01	??0.01	?0.009	?0.003	?0.0190	?0.009	?---	?0.015	?0.015	?0.0010	????0.48	??896
??D	0.0025	??0.01	??0.09	?0.005	?0.003	?0.0160	?0.010	?0.010	?0.015	?---	?0.0006	????0.45	??876
														??E	0.0016	??0.55	??0.80	?0.04	?0.003	?0.0195	?0.015	?0.009	?---	?0.018	?0.0012	????0.45	??905
??F	0.0011	??0.75	??0.75	?0.02	?0.002	?0.0135	?0.008	?0.015	?---	?---	?0.0010	????0.56	??889
														??G	0.0032	??0.01	??0.14	?0.009	?0.003	?0.0130	? 0.045	?---	?---	?---	?---	??? 0.29	??894
??H	0.0019	??0.45	??0.45	?0.04	?0.005	?0.0140	?0.015	?0.035	?---	?---	?0.0012	??? 0.27	??882

* for un-added Nb, Ti, V, B, top concentration is designated as "---", when calculating N/ (Al+Nb+Ti+V+B), concentration is taken as " 0 ".Table 7

No.	Steel	Hot rolling							Hot-rolled sheet annealing		Cold rolling	Cold-reduced sheet recrystallization annealing		Cooling: the speed of cooling before plated film ℃/s	Plated film		Alloying		Remarks
																				Roughing		Finish rolling			Draft %	Reel	Temperature ℃	Operation intermittently continuously	Plate temperature ℃	Bathe warm ℃	Temperature ℃	Hold-time s
		????CT ????℃
			??SRT ??℃	??RDT ??℃	??FET ??℃	Have unlubricated	??FDT ??℃	Draft %	Temperature ℃	Time s
											1	A	?1150		?900	??810	Have	??660		????95	????510	790	Intermittently	?80.0		860							?40	??15	?470	465	-	??-	??II
2	B	?1150	?910	??830	Have	??660	????95	????510	840	Continuously				?80.0					860						?40		??-	?-	-	-	??-	??I
											3	C	?1140		?920	??840	Have	??680		????95	????520	800	Intermittently	?82.5		870							?40	??30	?465	460	460	??25	??III
4	D	?1180	?900	??820	Have	??650	????95	????500	830	Continuously				?82.5					850						?40		??35	?470	465	-	??-	??II
											5	E	?1190		?930	??850	Have	??690		????95	????530	810	Intermittently	?80.0		880							?40	??25	?465	460	460	??23	??III
6	F	?1160	?920	??840	Have	??670	????95	????530	810	Intermittently				?82.5					880						?40		??-	?-	-	-	??-	??I
											7	G	?1120		?910	??820	Have	??670		????95	????520	800	Intermittently	?80.0		870							?40	??50	?480	470	-	??-	??II
8	H	?1100	?900	??810	Have	??650	????95	????500	790	Intermittently				?80.0					860						?40		??15	?465	470	470	??20	??III
											9	A	?1080		?900	??810	Have	??660		????95	????500	790	Intermittently	?82.5		860							?40	??15	?470	465	-	??-	??II
10	B	?1140	?910	??820	Have	??670	??? 65	????520	790	Intermittently				?82.5					860						?40		??1	?470	460	460	??20	??III
											11	C	?1250		1150	? 1070	Have	??910		????95	????750	850	Continuously	?80.0		870							?40	??30	?465	460	460	??25	??III
12	D	?1170	?900	??810	Have	??660	????95	????510	??? Do not handle					?80.0					850						?40		??-	?-	-	-	??-	??I

The base temperature is advanced in SRT=slab heating temperature, RDT=roughing ejection temperature, FET=finish rolling, FDT=finish rolling goes out material temperature, CT=coiling temperature I=cold-rolled steel sheet, II=hot-dip galvanized steel sheet, III=alloyed hot-dip galvanized steel plate table 8

No.	Steel	Solid solution N %	Tensile properties before strain aging is handled					Strain-aged hardening characteristics		Remarks
											????YS ????MPa	????TS ????MPa	????E1 ????％	The r value	TSxr value MPa	????BH ????MPa	????ΔTS ????MPa
			1	?A	??0.0069	????225	????321	????53	????2.4									????770	????122	????75	Embodiment
2	?B	??0.0089								????274	????391	????43	????2.3	????899	????183	????93	Embodiment
			3	?C	??0.0054	????221	????316	????54	????2.8									????885	????97	????72	Embodiment
4	?D	??0.0049								????221	????316	????54	????2.8	????885	????90	????66	Embodiment
			5	?E	??0.0050	????304	????435	????39	????2.0									????870	????80	????63	Embodiment
6	?F	??0.0088								????304	????434	????39	????2.1	????911	????133	????87	Embodiment
			7	?G	? 0.0000	????224	????320	????53	????2.8									????896	??? 3	??? 0	Comparative example
8	?H	? 0.0000								????284	????405	????42	????2.1	????851	??? 2	??? 0	Comparative example
			9	?A	??0.0070	????215	????311	????50	????2.3									??? 715	????152	????83	Comparative example
10	?B	??0.0082								????274	????391	????43	????1.9	??? 743	????143	????94	Comparative example
			11	?C	??0.0035	????236	????331	????51	????2.0									??? 662	????93	????48	Comparative example
12	?D	??0.0041								????241	????336	????51	????2.1	??? 706	????85	????49	Comparative example

Table 9

Steel	Chemical ingredients (quality %)
													??C	??Si	??Mn	??P	??S	??Al	??N	?N/Al	????Nb	??12/93?Nb	????B	Other
	??A	?0.0025	??0.15	??0.85	0.050	0.002	0.005	0.0120	??2.40	0.0040	??0.0005	??0.0015													?????-
??B													?0.0050	??0.51	??1.20	0.004	0.001	0.008	0.0150	??1.88	0.0070	??0.0009	??0.0009	?????-
	??C	?0.0024	??0.15	??0.35	0.040	0.001	0.004	0.0120	??3.00	0.0050	??0.0006	??0.0015													?????-
??D													?0.0150	??0.15	??0.88	0.010	0.002	0.010	0.0100	??1.00	0.0102	??0.0013	??0.0012	?????-
	??E	?0.0023	??0.01	??1.40	0.005	0.002	0.011	0.0120	??1.09	0.0070	??0.0009	??0.0010													?????-
??F													?0.0023	??0.05	??1.35	0.045	0.001	0.007	0.0120	??1.71	0.0080	??0.0010	??0.0020	??Mo：0.15
	??G	?0.0025	??0.15	??1.25	0.007	0.001	0.004	0.0110	??2.75	0.0070	??0.0009	??0.0015													??Ti：0.013
??H													?0.0025	??0.25	??1.25	0.008	0.001	0.011	0.0140	??1.27	0.0060	??0.0008	??0.0014	??Cu：0.50，Ni：0.20
	??I	?0.0024	??0.15	??1.25	0.005	0.003	0.011	0.0150	??1.36	0.0089	??0.0010	??0.0018													??Ni：0.05，V：0.02
??J													?0.022	??0.15	??1.21	0.008	0.002	0.005	0.0120	??2.40	0.0076	??0.0011	??0.0020	??Cu：0.10，Ni：0.05
	??K	0.070	??0.25	??1.50	0.015	0.003	0.055	0.0040	? 0.07	0.0090	??0.0012	??0.0021													?????-
??L													?0.0025	??0.15	??0.85	0.050	0.002	0.005	0.0120	??2.40	0.0001	??0.0000	≤0.0001	?????-
	??M	?0.0025	??0.15	??0.85	0.050	0.002	0.005	0.0120	??2.40	0.0050	??0.0006	≤0.0001													?????-
??O													?0.0025	??0.17	??0.81	0.008	0.001	0.007	0.0120	??1.71	0.110	??0.0142	??0.0015	?????-
	??P	?0.0026	??0.17	??0.82	0.007	0.001	0.007	0.0400	??5.71	0.0070	??0.0009	??0.0017													?????-
??Q													?0.0025	??0.18	??0.81	0.008	0.001	0.007	0.0120	??1.71	0.0080	??0.0010	??0.0022	??Ca：0.0035

Table 10

Steel plate No.	Steel	Hot-rolled process							Cold rolling process		α-γ coexistence humidity province ℃	The cold-reduced sheet annealing operation				Skin-pass		Remarks
																			Continuous annealing
												Slab heating temperature SRT ℃	Roughing	Thin slab has or not joint	Finish rolling								Reel	Cold rolling draft %	Cold-reduced sheet thickness of slab mm
		The thick mm of thin slab
			??Ar 3Transformation temperature ℃	FDT ℃ of ejection temperature	Hot-rolled sheet thickness of slab mm	CT ℃ of coiling temperature	Annealing temperature ℃	Hold-time s	Speed of cooling ℃/s	Cooling stops temperature ℃			Kind													Unit elongation %
															1	A	?1210		????28	Do not have	????873	????900	????4.0				????550	????83	?0.70	?860～950	?880	?35	?30	350	Skin rolling	0.5	Example of the present invention
2	B	?1230	????28	Do not have	????837	????900	????4.0	????530	????81	?0.75	?835～935	?870	?30	?35				350						Skin rolling	0.5	Example of the present invention
															3	C	?1220		????28	Do not have	????908	????910	????4.0				????550	????83	?0.70	?865～955	?885	?25	?25	350	Skin rolling	0.5	Example of the present invention
4	D	?1180	????28	Do not have	????851	????890	????4.0	????530	????83	?0.70	?845～922	?885	?40	?45				350						??-	-	Example of the present invention
															5	E	?1190		????28	Do not have	????801	????890	????4.0				????520	????83	?0.70	?825～906	?875	?25	?40	450	Leveling	0.5	Example of the present invention
6	F	?1180	????25	Do not have	????827	????890	????4.5	????500	????78	?1.00	?855～930	?885	?30	?35				450						Skin rolling+leveling	0.5	Example of the present invention
															7	G	?1180		????25	Do not have	????820	????890	????6.0				????570	????80	?1.20	?835～918	?875	?45	?30	450	Skin rolling+leveling	0.7	Example of the present invention
8	H	?1180	????25	Do not have	????824	????890	????4.0	????610	????80	?0.80	?835～923	?880	?25	?45				450						Skin rolling+leveling	0.7	Example of the present invention
															9	I	?1190		????28	Do not have	????819	????890	????4.0				????550	????84	?0.65	?830～915	?865	?25	?30	300	Skin rolling+leveling	0.7	Example of the present invention
10	J	?1210	????28	Do not have	????823	????870	????4.0	????450	????83	?0.70	?830～910	?870	?25	?30				300						Skin rolling+leveling	0.7	Example of the present invention
															11	K	?1200		????28	Do not have	????808	????880	????4.0				????520	????83	?0.70	?755～895	?870	?25	?30	300	Skin rolling+leveling	0.5	Comparative example
12	L	?1200	????28	Do not have	????873	????900	????4.0	????550	????83	?0.70	?860～950	?880	?35	?30				300						Skin rolling+leveling	0.5	Comparative example
															13	M	?1200		????25	Do not have	????873	????900	????4.0				????550	????83	?0.70	?860～950	?880	?35	?30	300	Skin rolling+leveling	0.5	Comparative example
14	O	?1210	????25	Do not have	????856	????890	????4.0	????520	????83	?0.70	?850～940	?890	?30	?35				300						Skin rolling+leveling	0.5	Comparative example
															15	P	?1240		????25	Do not have	????854	????880	????4.0				????520	????83	?0.70	?850～940	?890	?30	?35	300	Skin rolling	0.7	Comparative example
16	Q	?1220	????25	Do not have	????856	????900	????4.0	????530	????83	?0.70	?850～940	?880	?30	?35				300						Skin rolling	0.7	Example of the present invention
															17	A	? 950		????25	Do not have	????870	??? 750	????4.0				????540	????83	?0.70	?855～950	?880	?30	?30	300	Skin rolling	0.7	Comparative example
18	A	?1200	????28	Do not have	????873	????900	????4.0	??? 780	????83	?0.70	?865～950	?870	?35	?35				300						Skin rolling	0.7	Comparative example
															19	A	?1190		????28	Do not have	????873	????905	????4.0				????540	????83	?0.70	?860～950	820	?25	?40	300	Skin rolling	0.7	Comparative example
20	A	?1190	????28	Do not have	????873	????890	????4.0	????550	????83	?0.70	?860～950	?870	?30	5				300						Skin rolling	0.7	Comparative example

Table 11

Steel plate No.	Steel	Steel plate solid solution N amount quality %	The steel plate tissue			The sheet characteristic				Strain-aged hardening characteristics		Ageing resistance	Remarks
														Ferrite		The 2nd phase	Tensile properties				BH measures MPa	?ΔTS ??MPa	????????ΔY-E1 ??????????％
			Area occupation ratio %	Particle diameter μ m	AF area occupation ratio %	?YS ?MPa	?TS ?MPa	?E1 ?％	Average r value
										????1	?A	?0.0090		????92	??7	????8	315	?448	??38	1.8				????85	????75	????0.0	Example of the present invention
????2	?B	?0.0100	????95	??8	????5	355	?510	??34	1.7				????90								????80	????0.0	Example of the present invention
										????3	?C	?0.0085		????92	??7	????8	295	?420	??41	1.8				????80	????75	????0.0	Example of the present invention
????4	?D	?0.0095	????92	??6	????8	334	?475	??36	1.4				????95								????80	????0.0	Example of the present invention **
										????5	?E	?0.0100		????93	??7	????7	325	?465	??37	1.7				????88	????75	????0.0	Example of the present invention
????6	?F	?0.0105	????90	??7	????10	385	?550	??35	1.5				????102								????75	????0.0	Example of the present invention
										????7	?G	?0.0105		????88	??6	????12	315	?455	??39	1.8				????88	????72	????0.0	Example of the present invention
????8	?H	?0.0095	????92	??10	????8	325	?460	??37	1.8				????98								????75	????0.0	Example of the present invention
										????9	?I	?0.0090		????90	??5	????10	320	?465	??37	1.8				????97	????85	????0.0	Example of the present invention
????10	?J	?0.0105	????88	??5	????12	420	?595	??29	1.4				????105								????85	????0.0	Example of the present invention **
										????11	? K	? 0.0002		????75	??7	????25	370	?545	??25	1.1				??? 45	??? 34	??? 1.5	Comparative example
????12	? L	?0.0080	????98	??15	??? 2	290	?420	??35	1.3				??? 15								??? 10	??? 1.5	Comparative example
										????13	? M	?0.0085		????97	??8	??? 3	290	?410	??33	1.2				??? 15	??? 7	??? 1.0	Comparative example
????14	? O	? 0.0003	????98	??6	??? 2	320	?455	??33	1.1				????5								????15	??? 0.8	Comparative example
										????15	? P	?0.0190		????95	??7	????5	310	?440	??37	1.6				????90	????70	??? 2.8	Comparative example
????16	?Q	?0.0098	????92	??7	????8	315	?450	??39	1.7				????90								????70	????0	Example of the present invention
										????17	?A	? 0.0009		????98	? 22	??? 2	275	?420	??33	1.1				??? 0	??? 15	??? 0.5	Comparative example
????18	?0.0040	????95	? 25	????5	275	?410	??34	1.3	??? 30				??? 10								??? 0.5	Comparative example
										????19		?0.0050		????100	??12	??? 0	270	?380	??33	1.3			??? 25	??? 12	??? 0.8	Comparative example
????20	?0.0030	????99	? 22	??? 1	265	?385	??31	1.3	??? 20				??? 10								??? 0.9	Comparative example

AF: acicular ferrite

^*: galvanizing processing list 12 is arranged

Steel	Chemical ingredients (quality %)
													??C	??Si	??Mn	??P	?S	??Al	??N	??N/Al	???Nb	??12/93Nb	???B	Other
	N	?0.0085	?0.005	??0.55	??0.009	?0.005	??0.015	?0.0126	??0.84	??0.008	??0.0010	?0.0015													-

Table 13

Steel plate No.	Steel	Hot-rolled process							Cold rolling process		α-γ coexistence humidity province ℃	The cold-reduced sheet annealing operation				Modulate rolling		Remarks
																			Continuous annealing
												Slab heating temperature SRT ℃	Roughing	Thin slab has or not joint	Finish rolling								Reel		Cold draft %	Cold-reduced sheet thickness of slab mm
		The thick mm of thin slab
			??Ar 3Transformation temperature ℃	Go out FDT ℃ of material temperature	Hot-rolled sheet thickness of slab mm	CT ℃ of coiling temperature	Annealing temperature ℃	Hold-time s	Speed of cooling ℃/s	Cooling stops temperature ℃			Kind														Unit elongation %
															2-1	N	?1250		????25	Have *	870	?890	?4.5	??570				??69	1.4	??840～900	880	??30	??45	300	Skin rolling	0.5	Example of the present invention
2-2	?1230	????25	Have *	870	?890	?4.5	??550	??69	1.4	??840～900	880	??35	??45	310				Skin rolling							0.5	Example of the present invention
															2-3		?1240		????25	Have **	870	?890	?4.5	??560			??69	1.4	??840～900	880	??30	??45	310	Skin rolling	0.5	Example of the present invention

^*) the enforcement lubrication and rolling

^*) implement lubrication and rolling, use thin slab well heater, edges of boards heater table 14

Steel plate No.	Steel	Steel plate solid solution N amount quality %	The steel plate tissue			The sheet characteristic				Sheet plate characteristic			Strain-aged hardening characteristics		Ageing resistance	Remarks
																	Ferrite		The 2nd phase	Tensile properties				The discrete * of tensile properties			BH measures MPa	?ΔTS ??MPa	??ΔY-E1 ????％
			Area occupation ratio %	Particle diameter μ m	AF area occupation ratio %	?YS ?MPa	TS MPa	?E1 ?％	Average r value	??δYS ???MPa	??δTS ???MPa	??δE1 ???％
													2-1	N	0.0120		??91	??7	????9	315	445	??37	1.6	????10	????10	????5				????15	????15	????0	Example of the present invention
2-2	N	0.0120	??91	??7	????9	319	447	??37	1.6	????5	????5	????2				????7											????6	????0	Example of the present invention
													2-3	N	0.0125		??92	??7	????8	318	450	??38	1.5	????3	????5	????1				????8	????5	????0	Example of the present invention

^*) δ YS, δ TS, δ E1:=(maximum value-minimum value)

^*) AF: acicular ferrite, M: martensite, B: bainite, P: pearly-lustre body surface 15

Steel	Chemical ingredients (quality %)									Transformation temperature (℃)
												??C	??Si	??Mn	??P	??S	??Al	??N	??N/Al	Other	??Ac 1	??Ac 3
	??A	?0.050	??0.01	??0.55	0.040	0.001	0.004	0.0120	??3.00	????-	??735												??858
??B												?0.080	??0.02	??0.30	0.060	0.001	0.008	0.0153	??1.91	????-	??749	??866
	??C	?0.070	??0.15	??0.45	0.040	0.001	0.002	0.0118	??5.90	REM：0.0015	??740												??862
??D												?0.055	??0.15	??0.88	0.050	0.002	0.006	0.0095	??1.58	Ca：0.0020	??739	??863
	??E	?0.030	??0.01	??1.40	0.005	0.002	0.011	0.0120	??1.09	Ca：0.0025，REM：0.0020	??706												??832
??F												?0.050	??0.05	??0.55	0.045	0.001	0.007	0.0123	??1.76	Mo：0.02	??739	??862
	??G	?0.065	??0.02	??0.75	0.045	0.001	0.004	0.0114	??2.85	Ti：0.013，B：0.0005	??735												??855
??H												?0.050	??0.01	??0.85	0.008	0.001	0.008	0.0138	??1.73	Cu：0.50，Ni：0.20，Cr：0.20	??717	??834
	??I	?0.040	??0.01	??0.55	0.005	0.003	0.011	0.0151	??1.37	Ni：0.05，V：0.02	??717												??842
??J												?0.120	??0.15	??0.95	0.008	0.002	0.005	0.0118	??2.36	Cu：0.10，Ni：0.05，Nb：0.007	??719	??830
	??K	? 0.010	??0.25	??0.96	0.015	0.003	0.002	0.0042	??2.10	????-	??723												??857
??L												?0.080	??0.15	??0.85	0.050	0.002	0.045	0.0040	? 0.09	????-	??739	??859

Table 16

Steel plate No.	Steel	Hot-rolled process								Cold rolling process			The cold-reduced sheet annealing operation					Skin-pass
																			Slab heating temperature SRT ℃	Roughing	Thin slab has or not joint	Finish rolling		Cold rolling postcooling		Reel	Cold draft %	Cold-reduced sheet thickness of slab mm	Pack annealing	Continuous annealing				Overaging
		The thick mm of thin slab
			Go out FDT ℃ of material temperature	Hot-rolled sheet thickness of slab mm	Time opening Δ t s	Speed of cooling V ℃/s	CT ℃ of coiling temperature	Annealing temperature ℃	Annealing temperature ℃	Hold-time s	Speed of cooling ℃/s	Cooling stops temperature ℃	The residence time of the humidity province more than 350 ℃ **????s	Unit elongation %
															??1	??A	????1210	????30		Do not have		????850	????4.0	????0.2	????50	????550			????83	??0.70	??700	??790	??40	??45	??270	????-	??0.2
??2	??B	????1230	????30	Do not have	????870	????4.0	????0.2	????50	????530	????81	??0.75	??680	??780	??30					??50		??270						????-	??0.2
															??3	??C	????1220	????30		Do not have		????840	????4.0	????0.1	????50	????550			????83	??0.70	??700	??800	??30	??55	??270	????-	??0.2
??4	??D	????1180	????30	Do not have	????850	????4.0	????0.5	????50	????530	????83	??0.70	??690	??800	??45					??45		??250						????-	??0.2
															??5	??E	????1190	????30		Do not have		????850	????4.0	????0.2	????45	????520			????83	??0.70	??720	??770	??25	??45	??200	????-	??0.5
??6	??F	????1180 ***	????35	Do not have	????864	????4.5	????0.2	????45	????500	????78	??1.00	??700	??780	??35					??55		??200						????-	??-
															??7	??G	????1180	????35		Do not have		????860	????6.0	????1.2	????45	????570			????80	??1.20	??700	??830	??50	??60	??300	????-	??0.5
??8	??H	????1180	????35	Do not have	????830	????4.0	????0.3	????45	????610	????80	??0.80	??700	??810	??25					??50		??400						????50	??0.5
															??9	??I	????1190	????30		Have		????840	????4.0 *	????0.3	????45	????550			????84	??0.65	??700	??790	??25	??45	??250	????-	??0.5
??10	??J	????1210	????30	Do not have	????840	????4.0	????0.3	????50	????450	????83	??0.70	??700	??770	??25					??30		??250						????-	??0.5
															??11	? K	????1200	????30		Do not have		????850	????4.0	????0.3	????50	????520			????83	??0.70	??700	??800	??25	??30	??250	????-	??0.5
??12	?? L	????1200	????30	Do not have	????880	????4.0	????0.2	????50	????550	????83	??0.70	??700	??790	??35					??30		??270						????-	??0.7
															??13	??A	??? 950	????35		Do not have		??? 750	????4.0	????0.5	????50	????540			????83	??0.70	??700	??800	??30	??30	??270	????-	??0.7
??14	??A	????1200	????35	Do not have	????880	????4.0	????0.3	????50	??? 780	????83	??0.70	??700	??830	??35					??35		??250						????-	??0.7
															??15	??A	????1190	????35		Do not have		????870	????4.0	????0.2	????50	????540			????83	??0.70	??700	??680	??25	??40	??250	????-	??0.5
??16	??A	????1200	????35	Do not have	????880	????4.0	????0.2	????50	????550	????83	??0.70	??-	??820	??29					??35		??250						????-	??0.5
															??17	??B	????1190	????30		Do not have		????840	????4.0	????0.3	????50	????520			????83	??0.70	??710	??780	??35	??70	??450	????-	?? ****
??18	??G	????1180	????30	Do not have	????850	????4.0	????0.3	????50	????520	????83	??0.70	??720	??780	??40					??60		??450						????-	?? ****

^*) the enforcement lubrication and rolling

^*) cooling stops the following residence time more than 350 ℃ of temperature ^{* *}) hot base packs into ^{* * *}) carry out the skin-pass table 17 of unit elongation 0.5% behind the galvanizing

Steel plate No.	Steel	Steel plate solid solution N amount quality %	The steel plate tissue				The sheet characteristic				Strain-aged hardening characteristics		Ageing resistance	Remarks
															Ferrite		The 2nd phase		Tensile properties				BH measures MPa	??ΔTS ???MPa	??ΔY-E1 ????％
			Area occupation ratio %	Particle diameter μ m	M area occupation ratio %	Other phases: kind	?YS ?MPa	TS ?MPa	E1 ％	Average r value
											????1	?A	0.0075		????86	????7	??12	??B	290	?550	?35	1.6				????80	????80	????0.0	Example of the present invention
????2	?B	0.0055	????92	????8	??7	??P	295	?556	?35	1.5				????90									????85	????0.0	Example of the present invention
											????3	?C	0.0055		????90	????7	??10	??-	285	?555	?34	1.6				????85	????75	????0.0	Example of the present invention
????4	?D	0.0075	????89	????6	??10	??B	295	?565	?34	1.6				????95									????80	????0.0	Example of the present invention
											????5	?E	0.0110		????91	????7	??9	??-	315	?605	?33	1.7				????85	????75	????0.0	Example of the present invention
????6	?F	0.0110	????90	????7	??10	??-	309	?595	?35	1.6				????100									????75	????0.0	Example of the present invention
											????7	?G	0.0095		????85	????6	??14	??B	314	?605	?35	1.6				????85	????70	????0.0	Example of the present invention
????8	?H	0.0078	????87	????10	??12	??B	318	?615	?33	1.6				????96									????75	????0.0	Example of the present invention
											????9	?I	0.0086		????86	????5	??12	??P	276	?525	?37	1.5				????90	????80	????0.0	Example of the present invention
????10	?J	0.0095	????84	????5	??15	??P	324	?620	?33	1.5				????102									????90	????0.0	Example of the present invention
											????11	?K	0.0003		????98	????7	? 1	??P	235	?355	?38	1.4				????45	????34	????1.5	Comparative example
????12	?L	0.0005	????93	??? 15	??7	??-	241	?370	?39	1.3				????15									????10	????1.5	Comparative example
											????13	?A	0.0009		????98	??? 22	? 0.5	??P	285	?430	?32	1.1				????0	????15	????0.5	Comparative example
????14	0.0009	????95	??? 25	??5	??-	285	?445	?32	1.2	????30				????10									????0.5	Comparative example
											????15		0.0010		????100	??? 12	? 0	??-	315	?480	?34	1.4			????25	????12	????0.8	Comparative example
????16	0.0020	????99	??? 22	? 1	??-	350	?545	?25	1.0	????20				????10									????0.9	Comparative example
											????17		?B		0.0060	????92	????8	??7	??P	297	?555	?35			1.5	????92	????85	????0	Example of the present invention
????18	?G	0.0055	????92	????8	??7	??P	296	?557	?34	1.5		????90		????85									????0	Example of the present invention

M: martensite, B: bainite, P: pearly-lustre body surface 18

Steel	Chemical ingredients (quality %)									Transformation temperature (℃)
												??C	??Si	??Mn	??P	??S	??Al	??N	??N/Al	Other	??Ac 1	??Ac 3
	?M	?0.052	??0.01	??0.60	?0.035	?0.001	?0.002	?0.0125	??6.25	?-	??735												??855

Table 19

Steel plate No.	Steel	Hot-rolled process								Cold rolling process			The cold-reduced sheet annealing operation					Skin-pass	Remarks
																				Slab heating temperature SRT ℃	Roughing	Thin slab has or not joint	Finish rolling		Cold rolling postcooling		Reel	Cold draft %	Cold-reduced sheet thickness of slab mm	Pack annealing	Continuous annealing				Overaging
		The thick mm of thin slab
			Go out FDT ℃ of material temperature	Hot-rolled sheet thickness of slab mm	Time opening Δ t s	Speed of cooling V ℃/s	CT ℃ of coiling temperature	Annealing temperature ℃	Annealing temperature ℃	Hold-time s	Speed of cooling ℃/s	Cooling stops temperature ℃	The residence time s of the humidity province more than 350 ℃	Unit elongation %
															2-1	??M	?1180	????30			Do not have		??850	?4.5	??0.3	??45	??540			????64	?1.6	?700	790	??40	??45	270	???-	0.2	Example of the present invention
2-2	?1200	????30	Have *	??850	?4.5	??0.3	??45	??540	????64	?1.6	?700	790	??40	??45					270	???-		0.2						Example of the present invention
															2-3		?1190	????30			Have **		??855	?4.5	??0.3	??45	??540		????64	?1.6	?700	700	??40	??45	270	???-	0.2	Example of the present invention

^*) the enforcement lubrication and rolling

^*) use thin slab well heater, edges of boards heater table 20

Steel plate No.	Steel	Steel plate solid solution N amount quality %	The steel plate tissue				The sheet characteristic				Sheet plate characteristic			Strain-aged hardening characteristics		Ageing resistance	Remarks
																		Ferrite		The 2nd phase		Tensile properties				Dispersing of tensile properties *			BH measures MPa	?ΔTS ??MPa	??ΔY-E1 ????％
			Area occupation ratio %	Particle diameter μ m	M area occupation ratio %	Other phases: kind **	?YS ?MPa	?TS ?MPa	?E1 ?％	Average r value	?δYS ??MPa	?δTS ??MPa	??δE1 ???％
														??2-1	??M	??0.0075		???85	??7	??12	????B	295	?551	?35	1.6	??25	???15	????2				????80	????80	????0	Example of the present invention
??2-2	??M	??0.0075	???85	??7	??12	????B	295	?552	?35	1.6	??20	???10	????1				????80												????80	????0	Example of the present invention
														??2-3	??M	??0.0075		???85	??7	??12	????B	292	?553	?35	1.6	??15	???8	????1				????80	????80	????0	Example of the present invention

^*) δ YS, δ TS, δ E1:=(maximum value-minimum value)

^*) M: martensite, B: bainite, P: perlite

Claims (25)

1. cold-rolled steel sheet that has excellent strain aging hardening properties, it is characterized in that: % represents with quality, have contain that C:0.15% is following, Si:1.0% following, Mn:2.0% is following, P:0.1% is following, S:0.02% is following, Al:0.005～0.030%, N:0.0050～0.0400% and N/Al:0.30 N above, the solid solution attitude are more than 0.0010%, remainder is by forming that Fe and unavoidable impurities constitute.

2. according to the cold-rolled steel sheet that has excellent strain aging hardening properties of claim 1 record, it is characterized in that: on the basis of aforementioned component, also contain the composition more than 1 group or 2 groups in the following a group～d group of representing with quality %, wherein,

A group: among Cu, Ni, Cr, the Mo more than a kind or 2 kinds, the total amount is below 1.0%;

B group: among Nb, Ti, the V more than a kind or 2 kinds, the total amount is below 0.1%;

C group: the B below 0.0030%;

D group: Ca, REM a kind or 2 kinds, the total amount is 0.0010～0.010%.

3. cold-rolled steel sheet that has excellent strain aging hardening properties, it is characterized in that: % represents with quality, has to contain C: less than 0.01%, Si:0.005～1.0%, Mn:0.01～1.5%, P:0.1% are following, S:0.01% is following, Al:0.005～0.030%, N:0.005～0.040% and N/Al:0.30 N above, the solid solution attitude are more than 0.0010%, remainder is by forming that Fe and unavoidable impurities constitute.

4. according to the cold-rolled steel sheet that has excellent strain aging hardening properties of claim 3 record, it is characterized in that: on the basis of above-mentioned composition, also contain B:0.0001～0.0030%, Nb:0.005～0.050% of representing with quality % in the scope that satisfies following formula (1), (2), remainder is essentially Fe.

N％≥0.0015+14/93·Nb％+14/27·Al％+14/11·B％??---(1)

C％≤0.5·(12/93)·Nb％????????????????????????????---(2)

5. according to claim 3 or 4 cold-rolled steel sheets of putting down in writing that have excellent strain aging hardening properties, it is characterized in that: on above-mentioned composition basis, also containing the total amount of representing with quality % as required is Cu, the Ni below 1.0%, the composition more than a kind or 2 kinds among the Mo.

6. according to the cold-rolled steel sheet that has excellent strain aging hardening properties of claim 1～5 record, it is characterized in that: the size of microcrystal of steel plate is below the 20 μ m.

7. according to the cold-rolled steel sheet that has excellent strain aging hardening properties of claim 1～6 record, it is characterized in that: in thermal treatment temp: 120～200 ℃ cold zone has the intensity ascending amount after the shaping: more than the 60MPa.

8. an electro-galvanizing that has excellent strain aging hardening properties, galvanizing and alloyed hot-dip galvanized steel plate is characterized in that: the surface at the cold-rolled steel sheet of claim 1～7 record possesses electro-galvanizing, galvanizing and alloyed hot-dip zinc-coated layer.

9. the manufacture method of a cold-rolled steel sheet that has excellent strain aging hardening properties, it is characterized in that: % represents with quality, to contain C: less than 0.01%, Si:0.005～1.0%, Mn:0.01～1.5%, below the P:0.1%, below the S:0.01%, Al:0.005～0.030%, N:0.005～0.040%, and content range satisfies more than the N/Al:0.30, the steel billet that remainder is essentially the composition of Fe carries out hot rolling, at this moment, after finishing, finish rolling begins to cool down immediately, in the coiling temperature: reel down for 400～800 ℃, implement draft then: 60～95% cold rolling after, under 650～900 ℃ temperature, implement recrystallization annealing.

10. according to the manufacture method of the cold-rolled steel sheet that has excellent strain aging hardening properties of claim 9 record, it is characterized in that: on the basis of above-mentioned composition, also contain B:0.0001～0.0030%, Nb:0.005～0.050% of representing with quality % in the scope that satisfies following formula (1), (2), remainder is essentially Fe.

N％≥0.0015+14/93·Nb％+14/27·Al％+14/11·B％??---(1)

C％≤0.5·(12/93)·Nb％????????????????????????????---(2)

11. manufacture method according to claim 9 or 10 cold-rolled steel sheets of putting down in writing that have excellent strain aging hardening properties, it is characterized in that: in the temperature-rise period of above-mentioned recrystallization annealing, the humidity province of the 500 ℃～recrystallization temperature speed with 1～20 ℃/second is heated up.

12. the manufacture method of an alloy hot-dip galvanized steel sheet that has excellent strain aging hardening properties is characterized in that: in claim 9～11, after the recrystallization annealing, implement galvanizing and handle, then implement the heating Alloying Treatment.

13. deep-drawing cold-rolled steel sheet that has excellent strain aging hardening properties, it is characterized in that: % represents with quality, have and contain C: less than 0.01%, Si:0.005～1.0%, Mn:0.01～1.5%, P:0.1% are following, S:0.01% is following, Al:0.005～0.030%, N:0.005～0.040% and N/Al:0.30 N above, the solid solution attitude are more than 0.0010%, remainder is by forming that Fe and unavoidable impurities constitute, its TS * r value: more than the 750MPa.

14. the deep-drawing cold-rolled steel sheet that has excellent strain aging hardening properties according to claim 13 record, it is characterized in that: have on the basis of above-mentioned composition, also contain B:0.0001～0.0030%, Nb:0.005～0.050% of representing with quality % in the scope that satisfies following formula (1), (2), remainder is by forming that Fe and unavoidable impurities constitute, its TS * r value: more than the 750MPa.N％≥0.0015+14/93·Nb％+14/27·Al％+14/11·B％??---(1)C％≤0.5·(12/93)·Nb％????????????????????????????---(2)

15. the deep-drawing cold-rolled steel sheet that has excellent strain aging hardening properties according to claim 13 record, it is characterized in that: have on the basis that the steel of claim 13 record is formed, also contain B:0.0001～0.0030% of representing with quality %, Nb:0.005～0.050%, Ti:0.005～0.070%, the composition more than a kind or 2 kinds among V:0.005～0.10%, and N/ (Al+Nb+Ti+V+B): more than 0.30, the N of solid solution attitude is more than 0.0010%, remainder is by forming that Fe and unavoidable impurities constitute, its TS * r value: more than the 750MPa.

A 16. deep-drawing that the has excellent strain aging hardening properties manufacture method of cold-rolled steel sheet, it is characterized in that: % represents with quality, to have the C of containing: less than 0.01%, Si:0.005～1.0%, Mn:0.01～1.5%, below the P:0.1%, below the S:0.01%, Al:0.005～0.030%, N:0.005～0.040%, contain B:0.0001～0.0030%, Nb:0.005～0.050%, Ti:0.005～0.070%, composition more than a kind or 2 kinds among V:0.005～0.10%, and N/ (Al+Nb+Ti+V+B): after the steel billet material of the composition more than 0.30 was heated to more than 950 ℃, making roughing finish temperature was below 1000 ℃, Ar ₃More than, carry out roughing, then at Ar ₃Below, the humidity province more than 600 ℃ is while lubricating finish rolling, coiling, make that to begin to total draft that finish rolling is finished from roughing be more than 80% this moment, the hot-rolled sheet of gained is carried out recrystallization annealing, then carry out cold rollingly, the cold-reduced sheet of gained is carried out recrystallization annealing with draft 60～95%.

17. plasticity, strain-aged hardening characteristics and the good cold-rolled steel sheet of anti-room temperature ageing, it is characterized in that: % represents with quality, has the C:0.0015 of containing～0.025%, below the Si:1.0%, below the Mn:2.0%, below the P:0.1%, below the S:0.02%, below the Al:0.02%, N:0.0050～0.0250%, and contain B:0.0001～0.0050%, the composition more than a kind or 2 kinds of Nb:0.002～0.050%, and making N/Al is more than 0.3, the N of solid solution attitude is more than 0.0010%, remainder is by forming of constituting of Fe and unavoidable impurities and by the acicular ferrite of representing with area occupation ratio more than 5% mutually and median size: the tissue that the following ferritic phase of 20 μ m constitutes, its r value: more than 1.2.

18. the cold-rolled steel sheet according to claim 17 record is characterized in that: on the basis of aforementioned component, also contain the composition 1 group or 2 group or more of the following a group～c that represents with quality % among organizing, wherein,

A group: among Cu, Ni, Cr, the Mo more than a kind or 2 kinds, the total amount is below 1.0%;

B group: among Ti, the V a kind or 2 kinds, the total amount is below 0.1%;

C group: Ca, REM a kind or 2 kinds, the total amount is 0.0010～0.010%.

19. one kind has the r value: more than 1.2, plasticity, the manufacture method of the cold-rolled steel sheet that strain-aged hardening characteristics and anti-room temperature ageing are good, it is characterized in that: % represents with quality, to contain C:0.0015～0.025%, below the Si:1.0%, below the Mn:2.0%, below the P:0.1%, below the S:0.02%, below the Al:0.02%, N:0.0050～0.0250%, and contain B:0.0001～0.0050%, more than a kind or 2 kinds of Nb:0.002～0.050%, and N/Al is that the plate slab of the composition more than 0.3 is heated to slab heating temperature: more than 1000 ℃, carry out the roughing base that laminates, implement successively this thin slab execution finish rolling is gone out the material temperature: the finish rolling more than 800 ℃, and in the coiling temperature: make the hot-rolled process of hot-rolled sheet thereby reel below 800 ℃, thereby this hot-rolled sheet is implemented pickling and the cold rolling cold rolling process of making cold-reduced sheet, under the temperature in the ferritic-austenitic two-phase region this cold-reduced sheet is carried out continuous annealing, with speed of cooling: 10～300 ℃ of/second cold-reduced sheet annealing operations that are cooled to the humidity province below 500 ℃.

20. the manufacture method according to the cold-rolled steel sheet of claim 19 record is characterized in that: on the basis of aforementioned component, also contain the composition 1 group or 2 group or more of the following a group～c that represents with quality % among organizing, wherein,

A group: among Cu, Ni, Cr, the Mo more than a kind or 2 kinds, the total amount is below 1.0%;

B group: among Ti, the V more than a kind or 2 kinds, the total amount is below 0.1%;

C group: Ca, REM a kind or 2 kinds, the total amount is 0.0010～0.010%.

21. one kind has high r value and good strain-aged hardening characteristics and the non-ageing high strength cold rolled steel plate of normal temperature, it is characterized in that: % represents with quality, has the C:0.025 of containing～0.15%, below the Si:1.0%, below the Mn:2.0%, below the P:0.08%, below the S:0.02%, below the Al:0.02%, N:0.0050～0.0250%, and N/Al is more than 0.3, the N that contains the solid solution attitude more than 0.0010%, remainder is by forming that Fe and unavoidable impurities constitute, with contain the average crystal grain particle diameter of representing with area occupation ratio more than 80%: the ferritic phase that 10 μ m are following, also contain tissue, its r value: more than 1.2 as the martensitic phase of representing with area occupation ratio more than 2% of the 2nd phase.

22. the high strength cold rolled steel plate according to claim 21 record is characterized in that: on the basis of aforementioned component, also contain the composition 1 group or 2 group or more of the following d group～g that represents with quality % among organizing, wherein,

D group: among Cu, Ni, Cr, the Mo more than a kind or 2 kinds, the total amount is below 1.0%;

E group: among Nb, Ti, the V more than a kind or 2 kinds, the total amount is below 0.1%;

F group: the B below 0.0030%;

G group: among Ca, the REM a kind or 2 kinds, the total amount is 0.0010～0.010%.

23. one kind has the r value: the manufacture method of the non-ageing high strength cold rolled steel plate of high r value more than 1.2 and good strain-aged hardening characteristics and normal temperature, it is characterized in that: % represents with quality, to contain C:0.025～0.15%, below the Si:1.0%, below the Mn:2.0%, below the P:0.08%, below the S:0.02%, below the Al:0.02%, N:0.0050～0.0250%, and N/Al is that the plate slab of the composition more than 0.3 is heated to slab heating temperature: more than 1000 ℃, carry out the roughing base that laminates, implement successively this thin slab execution finish rolling is gone out the material temperature: the finish rolling more than 800 ℃, and in the coiling temperature: make the hot-rolled process of hot-rolled sheet thereby reel below 800 ℃, thereby this hot-rolled sheet is implemented pickling and the cold rolling cold rolling process of making cold-reduced sheet, to this cold-reduced sheet in annealing temperature: more than the recrystallization temperature～implement pack annealing below 800 ℃, then at annealing temperature: Ac ₁Transformation temperature～(Ac ₃Transformation temperature-20 ℃) carries out continuous annealing under, then with speed of cooling: 10～300 ℃ of/second cold-reduced sheet annealing operations that are cooled to the humidity province below 500 ℃.

24. manufacture method according to the high strength cold rolled steel plate of claim 23 record, it is characterized in that: continue with the cooling after the aforementioned continuous annealing, carry out the overaging processing of residence time more than 20 seconds in the humidity province that aforementioned refrigerative cooling stops below the temperature, more than 350 ℃.

25. the manufacture method of high strength cold rolled steel plates according to claim 23 or 24 records is characterized in that: on the basis of aforementioned component, also contain the composition 1 group or 2 group or more of the following d group～g that represents with quality % among organizing, wherein,

D group: among Cu, Ni, Cr, the Mo more than a kind or 2 kinds, the total amount is below 1.0%;

E group: among Nb, Ti, the V more than a kind or 2 kinds, the total amount is below 0.1%;

F group: the B below 0.0030%;

G group: Ca, REM a kind or 2 kinds, the total amount is 0.0010～0.010%.

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