CN104662187A

CN104662187A - Ferritic stainless steel

Info

Publication number: CN104662187A
Application number: CN201380049398.1A
Authority: CN
Inventors: 吉野正崇; 寒川孝; 石井知洋; 福田国夫; 太田裕树; 尾形浩行
Original assignee: NKK Corp
Current assignee: JFE Steel Corp; JFE Engineering Corp
Priority date: 2012-09-25
Filing date: 2013-09-17
Publication date: 2015-05-27
Also published as: KR20150060919A; MY155937A; TW201420781A; WO2014050011A1; TWI516614B; JP5534119B1; JPWO2014050011A1

Abstract

Provided is ferritic stainless steel which exhibits excellent corrosion resistance even under such welding conditions where sufficient gas shielding cannot be achieved. Ferritic stainless steel which is characterized by containing, in mass%, 0.001-0.030% of C, 0.05-0.30% of Si, 0.05-0.50% of Mn, 0.05% or less of P, 0.01% or less of S, 18.0-19.0% of Cr, 0.05% or more but less than 0.50% of Ni, 0.30-0.60% of Cu, 0.001-0.030% of N, 0.10-1.50% of Al, 0.05-0.50% of Ti, 0.002-0.050% of Nb and 0.01-0.50% of V, while satisfying formulae (1) and (2) below, with the balance made up of Fe and unavoidable impurities. 0.40 <= Si + 1.5Al + 1.2Ti <= 2.4 (1) 0.60 <= 1.2Nb + 1.7Ti + V + 2.2Al (2) In the formulae, element symbols represent the contents (mass%) of respective elements.

Description

Ferrite-group stainless steel

Technical field

From air, immerse at oxygen or nitrogen the ferrite-group stainless steel that erosion resistance decline also not easily occurs from the welding conditions of welding object material immersion weld seam for weld seam (weld bead) and nitrogen or carbon even if the present invention relates to.

Background technology

Ferrite-group stainless steel can guarantee erosion resistance with less Ni amount compared with austenite stainless steel.Due to the element that Ni is high price, so ferrite-group stainless steel can with low cost manufacture compared with austenite stainless steel.In addition, ferrite-group stainless steel also has compared with austenite stainless steel that thermal conductivity is high, coefficient of thermal expansion is little and the excellent characteristic such as stress corrosion crack (stresscorrosion cracking) not easily occurs.Therefore, ferrite-group stainless steel is applied in the purposes widely of the material of construction such as automotive exhaust system component, roof, door and window and the water storage such as kitchen, hydro-thermal water store tank material etc. always.

Under above-mentioned materials most cases be by shearing stainless steel plate, press process etc. and the parts be processed into are made by welding assembly.Welding process often adopts TIG to weld (tungsteninert gas welding).During welding, weld part is also required to have good erosion resistance in the same manner as mother metal portion.

But, by austenite stainless steel, particularly the steel grade such as SUS304 (18%Cr-8%Ni) (JIS (Japanese Industrial Standards) G 4305) and ferrite-group stainless steel carry out TIG when welding, sometimes because being called as the phenomenon of sensitization (sensitization), the decline compared with mother metal of the erosion resistance of weld part is caused.Sensitization refer to due to during welding thermal treatment makes Cr and the C in steel, N is combined into chromium carbide (Cr ₂₃c ₆deng) or chromium nitride (Cr ₂n etc.) and separate out at grain boundary, near the grain boundary of weld part, generate the low Cr of Cr concentration ratio mother metal lacks layer (Cr depletion layer), causes the phenomenon declined in the erosion resistance of grain boundary.By austenite stainless steel, such as, when the C such as SUS304 and the N content steel higher than ferrite-group stainless steel weld with ferrite-group stainless steel, sometimes there is sensitization.

When carrying out TIG welding, the non-active gas such as argon gas are usually used to suppress as shielding gas to invade fusion pool (the weld metal pool) part of metal melting state (during the welding) from the oxygen of air, nitrogen.But in recent years along with the complex structure of welding assembly, cannot carry out sufficient gas shield when welding, the welding that oxygen in an atmosphere, nitrogen are mixed under the so incomplete condition of fusion pool is increasing gradually.Invade the sensitization of the nitrogen growth encourage weld part of fusion pool from air, cause erosion resistance to decline.

In addition, oxygen generates the oxide film thereon being called as the Cr system of tempering color (temper color) at weld part, the growth because of it causes the Cr density loss of weld part, and erosion resistance declines.Therefore, even if require that the composition of steel being applied in the ferrite-group stainless steel of such purposes is the erosion resistance utilizing shielding gas cannot suppress also can guarantee when the intrusion from the nitrogen of air or oxygen weld part.

On the other hand, in recent years except the gloss part of No.2B glossiness in the past, BA glossiness etc., the demand of the so-called functional part (functional products) of the parts (internal part etc. of the exhaust system component of automobile, various electric product and machinery) for thinking little of outward appearance is increased gradually.In order to suppress manufacturing cost, functional part, using the anneling production line of carbon steel, after annealing, adopts such as high speed acid washing method manufacture disclosed in patent documentation 1 at about 850 ~ 900 DEG C.Therefore, not only in order to manufacture No.2B gloss part, BA gloss part, also in order to can manufacturing function part, requiring to have the recrystallization temperature that can anneal with the anneling production line of carbon steel and the composition of steel of high speed pickling can be carried out.

For such problem, disclosing by adding Ti, the Nb larger than Cr with the avidity of carbon, nitrogen, suppressing the generation of carbon chromium nitride thus suppressing the method that sensitization occurs.For example, Patent Document 2 discloses add Ti and Nb by compound and improve the steel of the resistance to grain boundary corrosion (interglanular corrosion resistance) of ferrite-group stainless steel.But ferrite-group stainless steel needs the Mo of interpolation more than 1.5% disclosed in patent documentation 2.Mo is the element of the erosion resistance improving mother metal, but is also strong ferrite generating elements, when therefore adding the Mo of 1.5%, generates ferritic phase and sensitization occurs, sometimes cannot obtain the erosion resistance of sufficient weld part at weld part.

In addition, as the ferrite-group stainless steel of the excellent corrosion resistance of weld part, For example, Patent Document 3 discloses the ferrite-group stainless steel of the excellent corrosion resistance of weld part, Patent Document 4 discloses the ferrite-group stainless steel with the excellent corrosion resistance of the weld part of austenite stainless steel.These disclosed example all need the Nb of interpolation more than 0.1%, and recrystallization temperature is high.Therefore, exist the anneling production line of common carbon steel cannot be used with the such problem of low cost manufacturing function part.

Prior art document

Patent documentation

Patent documentation 1: Japanese Patent No. 2842787 publication (Japanese Unexamined Patent Publication 8-10823 publication)

Patent documentation 2: Japanese Laid-Open Patent Publication 51-88413 publication

Patent documentation 3: Japanese Unexamined Patent Publication 2007-270290 publication

Patent documentation 4: Japanese Unexamined Patent Publication 2010-202916 publication

Summary of the invention

If suppress the generation of sensitization by merely increasing Ti, Nb according to existing technological thought, the surface imperfection that then TiN inclusion causes increases, the Nb of solid solution separates out with the form of thick Nb precipitate at weld part, produces the problem of welding crack (weld crack) etc.

Therefore; the object of the present invention is to provide a kind of ferrite-group stainless steel; its cause due to the shape of welding assembly etc. carrying out in the welding of ferrite-group stainless steel sufficient gas shield and then oxygen invade that fusion pool produces the welding conditions of tempering color (oxide film thereon) at weld part, nitrogen invades and there is the such welding conditions of sensitization, nitrogen invades the welding conditions of weld seam from welding object material, also has excellent erosion resistance.

The present inventor etc. are in order to solve above-mentioned problem, for various Addition ofelements, the impact that the generation of tempering color and the relation of erosion resistance that cause and nitrogen invade the generation of the sensitization caused and the relation of erosion resistance is invaded on the oxygen in TIG welding, use composition based on 18.0 ~ 19.0 quality %Cr-0.15 quality %Mn-0.1 quality %Ni-0.35 quality %Cu and the steel that Si, Al, Ti, Nb and V are changed at wide region conducts in-depth research.

It found that the change of the erosion resistance that the generation that oxygen invades the tempering color caused causes and the relation of various Addition ofelements (can be designated as O below by Si+1.5Al+1.2Ti _xvalue.Should illustrate, the symbol of element in formula represents the content (quality %) of each element) conclude, by making O _xvalue is more than 0.40, can improve erosion resistance.If this is due to O _xvalue is the interpolation of mode compound Si, Al and Ti of more than 0.40; then tempering color is not the oxide film thereon of the Cr system oxide compound to generate in existing steel; but the densification of Al, Si and Ti denseization and have the oxide film thereon of protectiveness, and then tempering color is suppressed to grow the decline of the mother metal Cr concentration caused.But, also specify that if with O _xthe mode compound of value more than 2.4 adds Si, Al and Ti, then the crystallinity of oxide film thereon raises, suppress ion etc. through effect decline, erosion resistance declines again.

In addition, O is used _xvalue be 0.65 ~ 0.70 steel reactivate rate (reactivation rate) (be the index of the degree representing sensitization, less than 0.01% represent almost sensitization does not occur) that nitrogen found that of invading that the relation of sensitization movement and the various Addition ofelements caused analyzes is defined in JIS G0580 (1986) (N can be designated as below by 1.2Nb+1.7Ti+V+2.2Al _trvalue, should illustrate, the symbol of element in formula represents the content (quality %) of each element) conclude, N _trwhen value is more than 0.60, reactivate rate becomes less than 0.01%.That is, by making N _trvalue is more than 0.60, even if to invade or in the welding of the austenite stainless steel large with nitrogen content, nitrogen invades weld part and causes common ferrite-group stainless steel under the welding conditions of weld part generation sensitization at the nitrogen from air, also good erosion resistance can be obtained.

Should illustrate, infer and obtain above-mentioned O _xand N _trthe coefficient of each element of value and the avidity of this element and oxygen or nitrogen proportional.

The present invention carries out based on above-mentioned viewpoint, and its main points are as follows.

[1] a kind of ferrite-group stainless steel, it is characterized in that, in mass %, containing C:0.001 ~ 0.030%, Si:0.05 ~ 0.30%, Mn:0.05 ~ 0.50%, below P:0.05%, below S:0.01%, Cr:18.0 ~ 19.0%, Ni: be more than or equal to 0.05% and lower than 0.50%, Cu:0.30 ~ 0.60%, N:0.001 ~ 0.030%, Al:0.10 ~ 1.50%, Ti:0.05 ~ 0.50%, Nb:0.002 ~ 0.05%, V:0.01 ~ 0.50%, and meet following formula (1) and (2), remainder is made up of Fe and inevitable impurity.

0.40≤Si+1.5Al+1.2Ti≤2.4····(1)

0.60≤1.2Nb+1.7Ti+V+2.2Al····(2)

Should illustrate, the symbol of element in formula represents the containing ratio (quality %) of each element.

[2] ferrite-group stainless steel according to above-mentioned [1], it is characterized in that, further in mass % containing more than a kind that is selected from Zr:0.01 ~ 0.50%, W:0.01 ~ 0.20%, REM:0.001 ~ 0.10%, Co:0.01 ~ 0.20%, B:0.0002 ~ 0.010%, Mo:0.01 ~ 1.0%.

[3] ferrite-group stainless steel according to above-mentioned [1] or [2], is characterized in that, further in mass % containing Sb:0.05 ~ 0.30%.

According to the present invention, invade the welding conditions of weld seam from welding object material even if invade weld seam and nitrogen or carbon at oxygen or nitrogen from air, also can obtain the ferrite-group stainless steel with excellent erosion resistance.

Embodiment

Below the restriction reason of each integrant of the present invention is described.

1. be grouped into about one-tenth

First, the reason that the one-tenth of regulation steel of the present invention is grouped into is described.Should illustrate, composition % is all quality %.

C：0.001～0.030％

It is larger that C measures more high strength, and fewer processibility is better.In order to obtain sufficient intensity, need more than 0.001% be contained, if but contain C more than 0.030%, the decline of processibility is obvious, and easily the erosion resistance decline caused by Local C r shortage caused is separated out in generation by chromium carbide.Therefore, C amount is set to the scope of 0.001 ~ 0.030%.Wherein, from the viewpoint of erosion resistance and processibility C amount more low better, if but C to be made to measure extremely decline, refining expends time in, preferred in manufacture, is therefore preferably the scope of 0.003 ~ 0.018%.Be more preferably the scope of 0.005 ~ 0.012%.

Mn：0.05～0.50％

Mn is the element inevitably contained.If Mn amount is more than 0.50%, then promote the precipitation becoming the MnS of the starting point of corrosion, erosion resistance declines.Therefore, Mn amount is set to less than 0.50%.On the other hand, Mn amount is reduced to and manufacturing cost can be caused obviously to rise lower than 0.05%.Therefore, Mn amount is set to the scope of 0.05 ~ 0.50%.Be preferably the scope of 0.05 ~ 0.40%.Be more preferably the scope of 0.05 ~ 0.35%.

Below P:0.05%

P is the element inevitably contained in steel, excessive in making weldability decline, and easily grain boundary corrosion occurs.This trend containing P more than 0.05% time become obvious.Therefore, P amount is set to less than 0.05%.Be preferably less than 0.03%.

Below S:0.01%

S and P is also similarly the element inevitably contained in steel, causes erosion resistance to decline containing S more than 0.01%.Therefore, S amount is set to less than 0.01%.Be preferably less than 0.008%.

Cr：18.0～19.0％

Cr is in order to ensure the most important element of erosion resistance.Lower than 18.0% time, can not get sufficient erosion resistance because of the oxidation weld seam that causes the Cr on top layer to reduce in welding and periphery thereof.Particularly carry out different steel grade from austenite stainless steels such as SUS304 when welding, the intrusion of nitrogen encourages sensitization further.In addition, lower than 18.0% time, passivation (passivation) becomes unstable, after the N that describes _trthe relation of value and reactivate rate (reactivation rate) is disintegrated, and sensitization causes erosion resistance to decline.On the other hand, if containing Cr more than 19.0%, then because the dissolution rate of steel matrix during pickling declines, so cannot Ex-all oxide skin disclosed to use in the high speed acid washing method of the pickling lines of carbon steel of patent documentation 1, sometimes at residual oxidization skins such as the ends of steel plate.Therefore, Cr amount is set to the scope of 18.0 ~ 19.0%.Be preferably the scope of 18.0 ~ 18.7%.Be more preferably the scope of 18.3 ~ 18.7%.

Ni: be more than or equal to 0.05% and lower than 0.50%

Ni is the element improving stainless erosion resistance, is the element that the carrying out suppressing corrosion in the corrosive environment of active dissolution (active dissolution) occurs forming passivation tunicle (passive film).In addition, Ni is strong austenite generting element, has and suppresses ferrite to generate at weld part, the effect of the sensitization suppressing the precipitation of carbon chromium nitride to cause.These effects are by obtaining containing more than 0.05%.But, containing more than 0.50% time, processibility declines, and the susceptibility grow of stress corrosion crack.Further, due to the element that Ni is high price, manufacturing cost is caused to increase.Therefore, Ni amount be set to be more than or equal to 0.05% and lower than 0.50% scope.Be preferably the scope of 0.10 ~ 0.30%.Be more preferably the scope of 0.15 ~ 0.25%.

Cu：0.30～0.60％

Cu is the element improving erosion resistance, is the effective especially element of erosion resistance to mother metal when improving in the aqueous solution or be attached with weakly acidic water droplet and weld part.In addition, Cu and Ni is strong austenite generting element equally, has and suppresses ferrite to generate at weld part, the effect of the sensitization suppressing the precipitation of carbon chromium nitride to cause.These effects are by obtaining containing more than 0.30%.On the other hand, if containing Cu more than 0.60%, then hot workability declines, and generates the Cu generation oxide compound being called as red oxidization skin (red scale) during hot rolling at surface of steel plate, produces surface imperfection, thus not preferred.Therefore, Cu amount is set to the scope of 0.30 ~ 0.60%.Be preferably the scope of 0.30 ~ 0.50%.Be more preferably the scope of 0.35 ~ 0.45%.

N：0.001～0.030％

N content more high strength is larger, and fewer processibility is better.In order to obtain sufficient intensity, it is desirable to containing more than 0.001%, if but content more than 0.030%, processibility (elongation) obviously declines, and causes erosion resistance to decline due to the precipitation encouraging chromium nitride, thus not preferred.Therefore, N amount is set to the scope of 0.001 ~ 0.030%.From the viewpoint of erosion resistance, N is more few better, but in order to reduce N amount, needs to increase refining time, causes manufacturing cost to rise and productivity decline, is therefore preferably the scope of 0.003 ~ 0.030%.Be more preferably the scope of 0.003 ~ 0.015%.The more preferably scope of 0.005 ~ 0.010%.

Si+1.5Al+1.2Ti (O _xvalue): 0.40 ~ 2.4

Should illustrate, the symbol of element in formula represents the containing ratio of each element.

Si, Al and Ti are extremely important element in the present invention.This 3 kinds of elements all strong with the avidity of oxygen.Therefore, with the addition of the stainless steel of these elements oxidized time, formed at surface of steel plate with the tunicle of Si, Al and Ti oxide compound that is principal constituent.Tunicle due to this oxide compound is fine and close and protectiveness is high, so suppress the erosion resistance caused by Cr density loss in the mother metal caused by the oxidation of Cr to decline.This effect is at O _xcan obtain when value is more than 0.40.But, if O _xvalue is more than 2.4, then the crystallinity of oxide compound tunicle raises, suppress metal ion etc. through effect decline, so erosion resistance declines again.Therefore, O _xvalue is set to the scope of 0.40 ~ 2.4.Be preferably the scope of 0.40 ~ 1.8.The more preferably scope of 0.50 ~ 1.5.

1.2Nb+1.7Ti+V+2.2Al (N _trvalue): more than 0.60

The reason of the sensitization of weld part invades the nitrogen of fusion pool from air or forms nitride from the nitrogen that welding object material invades with Cr and separate out, generation Local C r shortage region.When compound is added with Nb, Ti, V and Al that the avidity of N is larger than Cr, nitrogen does not react with Cr but separates out with the form of the nitride of these 4 kinds of elements.Therefore, it is possible to suppress Cr to lack the generation in region, the erosion resistance of weld part improves.This effect is at N _trcan obtain when value is more than 0.60.More preferably more than 0.80.

Should illustrate, if N _trvalue produces the surface imperfection caused by the inclusion of Ti system or Al system more than 4.00, higher limit is set to 4.00.Be preferably less than 2.50.

Si, Al, Ti, Nb and V are to meet above-mentioned O _xvalue and N _trthe mode compound of the preferable range of value is added, but specifies the addition of each element in the present invention further according to following reason.

Si：0.05～0.30％

The element that the tempering color that Si described above is formed when being and being condensed into welding together with Al, Ti and the protectiveness improving oxide film thereon make the erosion resistance of weld part good.This effect is by obtaining containing more than 0.05%.But, if containing Si more than 0.30%, the pickling that the rolling load then occurred in hot-rolled process increases and forms Si denseization layer on steel plate top layer in annealing operation and cause declines, thus causes the increase of surface imperfection, the rising of manufacturing cost, thus not preferred.Therefore, Si amount is set to the scope of 0.05 ~ 0.30%.Be preferably the scope of 0.05 ~ 0.25%.The more preferably scope of 0.08 ~ 0.20%.

Al：0.10～1.50％

Al and Si is same, the tempering color formed when being also and being condensed into welding together with Si with Ti and improve the element of the erosion resistance of weld part.In addition, because Al is stronger than Cr with the avidity of nitrogen, so when nitrogen is mixed into weld part, nitrogen is not separated out with the form of aluminium nitride with the form of chromium nitride, has the effect suppressing sensitization.In addition, Al is the element also useful to the deoxidation in steel making working procedure.These effects are by obtaining containing more than 0.10%.But if containing Al more than 1.50%, then ferrite crystal grain coarsening, processibility, manufacturing decline.Therefore, Al amount is set to the scope of 0.10 ~ 1.50%.Be preferably the scope of 0.12 ~ 0.80%.The more preferably scope of 0.15 ~ 0.50%.

Ti：0.05～0.50％

Ti and Si and Al is same, the tempering color formed when being also and being condensed into welding and improve the element of the protectiveness of oxide film thereon.In addition, Ti is still preferentially combined the element that the erosion resistance caused by sensitization that suppresses the precipitation of carbon chromium nitride to cause declines with C and N.These effects can be obtained by interpolation more than 0.05%.But, if added more than 0.50%, then generate thick titanium carbonitride, cause surface imperfection, thus not preferred.Therefore, Ti amount is set to the scope of 0.05 ~ 0.50%.Be preferably the scope of 0.10 ~ 0.40%.The more preferably scope of 0.15 ~ 0.35%.

Nb：0.002～0.050％

Nb is preferentially combined the element that the erosion resistance caused by sensitization that suppresses the precipitation of carbon chromium nitride to cause declines with C and N.This effect is by obtaining containing more than 0.002%.On the other hand, Nb is also the element making recrystallization temperature increase, if containing Nb more than 0.050%, then the annealing temperature needed for recrystallize heats up, and becomes difficulty by the annealing and the cheap manufacturing function part of pickling using the anneling production line of carbon steel.Therefore, Nb amount is set to the scope of 0.002 ~ 0.050%.Be preferably the scope of 0.010 ~ 0.045%.The more preferably scope of 0.015 ~ 0.040%.

V：0.01～0.50％

V is the element improving erosion resistance, processibility.When nitrogen invades weld part, nitrogen is separated out with the form of VN, suppress sensitization.This effect is by obtaining containing more than 0.01%.But if containing V more than 0.50%, then processibility declines.Therefore, V amount is set to the scope of 0.01 ~ 0.50%.Be preferably the scope of 0.05 ~ 0.30%.The more preferably scope of 0.08 ~ 0.20%.

Be more than basic chemical composition of the present invention, remainder is made up of Fe and inevitable impurity, as inevitable impurity, can allow below Ca:0.0020%.

In addition, for suppressing the sensitization of weld seam and improving erosion resistance etc., can containing following element.

Zr：0.01～0.50％

Zr has and is combined with C, N and suppresses the effect of sensitization.This effect is by obtaining containing more than 0.01%, if containing Zr more than 0.50%, processibility declines.In addition, because Zr is the element of high price, so excessive interpolation causes manufacturing cost to increase, thus not preferred.Therefore, containing the scope being preferably set to 0.01 ~ 0.50% during Zr.Be more preferably the scope of 0.05 ~ 0.35%.

W：0.01～0.20％

W and Mo has the effect improving erosion resistance equally.This effect is by containing more than 0.01% and can obtain, if contain W more than 0.20%, intensity rising, causes the decline of manufacturing because of the increase etc. of rolling load, thus not preferred.Therefore, containing the scope being preferably set to 0.01 ~ 0.20% during W.Be more preferably the scope of 0.05 ~ 0.15%.

REM：0.001～0.10％

REM has the effect improving scale resistance, and by the speed of growth of inhibited oxidation skin, the formation Cr suppressed immediately below the tempering color of weld part being lacked to region is effective.Need containing more than 0.001% in order to obtain this effect.But if containing REM more than 0.10%, the manufacturings such as pickling decline.In addition, because REM is the element of high price, so excessive in causing manufacturing cost to increase, thus not preferred.Therefore, containing the scope being preferably set to 0.001 ~ 0.10% during REM.Be more preferably the scope of 0.03 ~ 0.08%.

Co：0.01～0.20％

Co is the element improving toughness.This effect is by obtaining containing more than 0.01%.On the other hand, if containing Co more than 0.20%, manufacturing declines, therefore, containing the scope being preferably set to 0.01 ~ 0.20% during Co.Be more preferably the scope of 0.05 ~ 0.15%.

B：0.0002～0.010％

B is the element improving secondary processing brittleness (secondary working embrittlement), and its effect is by obtaining containing more than 0.0002%.But if cross 0.010% containing B ultrasonic, then excessive solution strengthening (solid solution strengthening) causes ductility (ductility) to decline.Therefore, containing the scope being preferably set to 0.0002 ~ 0.010% during B.Be more preferably the scope of 0.0002 ~ 0.007%.The more preferably scope of 0.0003 ~ 0.003%.

Mo：0.01～1.0％

Mo, when Cr content is more than 18%, is the element promoting the passivation again (repassivation) of passivation tunicle and improve stainless erosion resistance.This effect is by obtaining containing more than 0.01%.But if containing Mo more than 1.0%, then rolling load becomes large, and manufacturing declines, and the excessive increase of armor plate strength occurs.In addition, because Mo is the element of high price, so a large amount of containing making manufacturing cost increase.Therefore, the scope of 0.01 ~ 1.0% is preferably set to when measuring containing Mo.Be more preferably the scope of 0.05 ~ 0.5%.

In addition, in order to make nitrogen stablize, can containing Sb as selection element.

Sb：0.05～0.30％

Sb and Al is identical, when the gas shield of TIG welding is insufficient, has the effect catching the N be mixed into from air, when using in the structure with the complicated shape carrying out sufficient gas shield difficulty, is effective especially Addition ofelements.This effect, by obtaining containing more than 0.05%, if contain Sb more than 0.30%, then generates non-metallic inclusion in steel making working procedure, makes surface texture poor.In addition, the toughness deterioration of hot-rolled sheet is made.Therefore, during containing Sb, be preferably set to the scope of 0.05 ~ 0.30%.Be more preferably the scope of 0.05 ~ 0.15%.

2. manufacturing condition

Next, the preferable production process of steel of the present invention is described.With the molten steel that the preferred component that the known method meltings such as converter, electric furnace, vacuum melting stove are above-mentioned forms, Continuous casting process or ingot casting method is utilized to make steel material (slab).This slab is heated 1 ~ 24 hour at 1100 ~ 1250 DEG C or do not heat and under the former state of casting, directly carry out hot rolling and make hot-rolled sheet.

Usually, hot-rolled sheet is implemented to the annealing of the hot-rolled sheet of 1 ~ 10 minute at 800 ~ 1100 DEG C, also can omit the annealing of hot-rolled sheet according to purposes.Then, after the pickling of hot-rolled sheet, by cold rolling make cold-reduced sheet after, implement recrystallization annealing, pickling and obtain goods.

In order to ensure elongation characteristic, curved characteristic, compression moulding and obtain good shape, preferably carries out cold rolling with the draft of more than 50%.General when surface gloss, the No.2B gloss part of JIS G 0203, in order to obtain obtaining good surface texture in good mechanical properties and pickling, preferably carry out the recrystallization annealing of cold-reduced sheet at 800 ~ 950 DEG C.

But, when manufacturing so-called functional part (utilizing the steel plate that cold continuous rolling (tandem cold rolling)-continuous annealing operation manufactures), manufacture most preferably by the disclosed low operation of the cost of the continuous annealing pickling lines of carbon steel that uses of such as patent documentation 1, annealing temperature now is most preferably carried out at 800 ~ 900 DEG C.In addition, for the further parts pursuing the position of gloss, it is effective to glossiness for carrying out BA annealing (clean annealing (bright annealing)).Should illustrating, in order to improve surface texture further, also can implement grinding etc. afterwards and after processing cold rolling.

Embodiment 1

Below, based on embodiment, the present invention is described in more detail.

In 50kg small size vacuum calciner, melting has the stainless steel of the chemical constitution shown in table 1-1 ~ table 1-4.Should illustrate, the O of table 1-2 and table 1-4 _xvalue and N _trvalue is defined (content (quality %) that the symbol of element wherein, in formula represents each element) by Si+1.5Al+1.2Ti and 1.2Nb+1.7Ti+V+2.2Al respectively.By after these heating of plate blanks to 1150 DEG C in the stove with Ar gas sweetening, implement hot rolling, make the hot-rolled sheet that 3.5mm is thick.Then, after these hot-rolled sheets being implemented at 950 DEG C to the annealing of the hot-rolled sheet of 1 minute, after effects on surface carries out the Shot Blasting of use granulated glass sphere, at temperature 80 DEG C, flood in 20 quality % sulphuric acid solns after 120 seconds, in the mixing acid of the temperature 55 DEG C be made up of 15 quality % nitric acid and 3 quality % hydrofluoric acid, dipping carries out pickling in 60 seconds, carries out deoxygenated skin.

Be cold-rolled to thickness of slab 0.8mm further, in weak reducing atmosphere (hydrogen: 5vol%, nitrogen: 95vol%, dew point :-40 DEG C), carry out the recrystallization annealing of 1 minute at 900 DEG C, obtain cold rolled annealed plate.Next carrying out the process of high speed deoxygenated skin, that is, is in the mix acid liquor be made up of 15 quality % nitric acid and 0.5 quality % hydrochloric acid of 50 DEG C, this cold rolled annealed plate is carried out to the electrolysis (10A/dm of 2 times in temperature ², 2 seconds), obtain cold rolled annealed acid-cleaning plate.JIS 13B tension test sheet is gathered abreast from the cold-reduced sheet made and rolling direction, carry out tension test based on JIS Z2201, measure 0.2% endurance (YS), tensile strength (TS) and elongation at break (El) respectively.

Docking TIG welding (butt TIG welding) is carried out to the cold-reduced sheet of the cold rolled annealed acid-cleaning plate made and commercially available SUS304 (C:0.07 quality %, N:0.05 quality %).Welding current is set to 90A, and welding speed is set to 60cm/min.Shielding gas is the intrusion of the nitrogen supposed in air, oxygen, uses the argon gas containing the nitrogen of 8vol%, the oxygen of 2vol% with 15L/min.The width of the weld seam of the face side obtained is about 3mm.

Gather and comprise the square test film of the 20mm of the weld seam made; cover with the mode protection material leaving the square mensuration face of 10mm; under the state of the tempering color formed when residual welding, in the 3.5 quality %NaCl solution of 30 DEG C, measure pitting potential (pitting potential).Do not carry out grinding, the Passivation Treatment of test film, the measuring method beyond it is according to JIS G 0577 (2005).

In addition, the mode being positioned at the center of minor face abreast with weld seam and long limit gathers the test film of 60 × 80mm.After grinding with the surface of the pouncing papers of No. 600 to this test film, erosion resistance is evaluated in the neutral salt spray round-robin test (neutral salt spray cyclic corrosion test) carrying out 5 circulations.Brine spray round-robin test based on JIS H 8502, by 5%NaCl spraying (35 DEG C, 2hr) → dry (60 DEG C, 4hr, relative humidity 20 ~ 30%) → moistening (40 DEG C, 2hr, relative humidity more than 95%) be set to 1 circulation.

Carry out these to evaluate, be more than 150mVvs SCE at the pitting potential of mother metal, the pitting potential of weld seam is more than 0mVvs SCE, neutral salt spray round-robin test does not cause corrosion, elongation at break in tension test is more than 25%, and surface texture good time, be judged as the material obtaining regulation provided by the invention.

Evaluation result is shown in table 2-1, table 2-2.

The pitting potential meeting the weld seam of No.1 ~ 22 of key element of the present invention is 0mV more than vs SCE, and neutral salt spray round-robin test does not cause corrosion, shows sufficient erosion resistance with the weld part of austenite stainless steel.In addition, the elongation at break in tension test is more than 25%, well, does not also observe surface imperfection.

But the content of each element is in scope of the present invention, but O _xvalue, N _trany one or both in value are lower than the No.23,24,31 and 32 and O of scope of the present invention _xalthough value exceedes in the No.25 of scope of the present invention the pitting potential of the mother metal obtaining more than 150mVvs SCE, but the pitting potential of weld seam is all lower than 0mV vs SCE, therefore produce corrosion at welding seam part in neutral salt spray test, can not get the corrosion resistance at welded part specified.

Si content exceedes in the No.26 of scope of the present invention, owing to defining the firm oxide scale layer of Si denseization during annealing in steel plate skin section, so the oxide skin after generation pickling process remains, producing in neutral salt spray round-robin test with oxide skin is the corrosion of starting point.Equally, Al is in extraneous No.28 of the present invention lower than No.27 and Cu of scope of the present invention, although the O for specifying _xvalue and N _trvalue, but corrosion is created in neutral salt spray round-robin test.

Al, Ti or Cu content exceedes in No.29 ~ 31 of scope of the present invention, in hot rolling or a large amount of surface imperfection of cold rolling rear generation, cannot obtain suitable surface texture.

By these results verifications in order to free of surface defects obtain the material behavior of regulation provided by the invention, the not only content of each element, O _xvalue and N _trvalue also needs to be adjusted in scope of the present invention.

Utilizability in industry

The ferrite-group stainless steel obtained in the present invention is applicable to the purposes by welding manufacture structure, such as, and the automobile exhaust system materials such as sourdine, the structure materials etc. such as door and window, scavenge port, pipeline.

Claims

1. a ferrite-group stainless steel, it is characterized in that, in mass %, containing C:0.001 ~ 0.030%, Si:0.05 ~ 0.30%, Mn:0.05 ~ 0.50%, below P:0.05%, below S:0.01%, Cr:18.0 ~ 19.0%, Ni: be more than or equal to 0.05% and lower than 0.50%, Cu:0.30 ~ 0.60%, N:0.001 ~ 0.030%, Al:0.10 ~ 1.50%, Ti:0.05 ~ 0.50%, Nb:0.002 ~ 0.050%, V:0.01 ~ 0.50%, and meet following formula (1) and (2), remainder is made up of Fe and inevitable impurity,

0.40≤Si+1.5Al+1.2Ti≤2.4 ···(1)

0.60≤1.2Nb+1.7Ti+V+2.2Al ···(2)

Should illustrate, the symbol of element in formula represents the containing ratio of each element, and unit is quality %.

2. ferrite-group stainless steel according to claim 1, it is characterized in that, further in mass % containing more than a kind that is selected from Zr:0.01 ~ 0.50%, W:0.01 ~ 0.20%, REM:0.001 ~ 0.10%, Co:0.01 ~ 0.20%, B:0.0002 ~ 0.010%, Mo:0.01 ~ 1.0%.

3. ferrite-group stainless steel according to claim 1 and 2, is characterized in that, further in mass % containing Sb:0.05 ~ 0.30%.