JP6699310B2 - Cold rolled steel sheet for squeezer and method for manufacturing the same - Google Patents

Description

  The present invention relates to a cold rolled steel sheet for drawn cans and a method for manufacturing the same.

  Battery cans such as AA-AA batteries, button batteries, and large-sized hybrid batteries, and various containers have cold-rolled steel plates or steel plates with Ni plating, Ni diffusion plating, Sn plating, and tin-free steel (TFS) plating ( A plated steel sheet (hereinafter referred to as a cold rolled steel sheet) that has been subjected to various platings such as a metal Cr layer and a Cr hydrated oxide layer) is subjected to severe multistage drawing and DI (Drawing and Ironing): It is manufactured by subjecting it to drawing and ironing. Alternatively, after the cold-rolled steel sheet is manufactured into a can, various kinds of plating such as Ni plating, Sn plating, TFS plating or coating is applied to form a can container.

  The main characteristics required for cold-rolled steel sheets used for these can containers are (1) press formability (formability without defects such as cracks occurring during processing), (2) rough surface resistance ( (Surface roughness after pressing is small), (3) Earring property (material anisotropy is small and ears are small after deep drawing), (4) Non-aging (stretcher strain during drawing). It should not occur).

It is known that the press formability (1) generally has better properties as the average plastic strain ratio r _m (hereinafter sometimes referred to as the average r value) is higher, and thus Nb-added ultra-low carbon steel. This can be achieved by using IF (Interstitial Free) steel represented by (Nb-SULC). However, the crystal grains of IF steel are generally coarser than those of low carbon steel. Therefore, in order to increase the average r value, it is necessary to increase the temperature during annealing to further coarsen the crystal grains.

The surface roughening resistance (2) is improved as the crystal grains are made finer. However, in applications such as battery cans, it is necessary to secure the sealing property of the sealing part of the upper lid, and therefore a surface quality after drawing that is much more excellent than before is required, and a grain size number of 11.0 or more (average The crystal grain size must be ≤7.8 μm). The rougher the surface, the worse the crystal grains are. Therefore, it is difficult to achieve both press formability and surface roughening resistance by using IF steel having large crystal grains. On the other hand, if low carbon steel is used, the crystal grains can be made finer, but it is difficult to obtain a high average plastic strain ratio r _m . Therefore, even if low carbon steel is used, it is difficult to achieve both press formability and surface roughening resistance.

  The earring property (3) is better as the in-plane anisotropy Δr value is smaller, and ears are less likely to occur during deep drawing. If the earring property is good, the steel plate yield associated with the earring of the drawn can can be improved, and it is possible to reduce progressive troubles between processes due to the earring in multi-step drawing and DI processing, and to reduce the scratches caused by tearing of the earring tip. .

  The non-aging property of (4) means that stretcher strain does not occur during drawing. When stretcher strain occurs, irregularities are formed on the can peripheral surface and the can bottom. If the battery can (squeeze can) has such an uneven shape, the contact electric resistance becomes large, which is not preferable, and in addition, the can rigidity of the can decreases and the internal and external pressure resistance of the can also decreases. .. Therefore, the steel sheet for drawn cans is required not to generate stretcher strain after drawing. The stretcher strain occurs due to yield point elongation when the steel sheet is deformed (YP-EL: elongation amount of steady deformation that progresses immediately after yielding with a deformation resistance smaller than the yield point). In order to suppress the occurrence of stretcher strain over a long period of time, it is necessary that the yield point elongation after aging treatment is zero.

On the other hand, battery cans used in hybrid vehicles and the like are increasingly required to have improved performance, and steel sheets that can withstand more severe press working are required. In order to improve the above-mentioned performance, a cold-rolled steel sheet having excellent drawability, a high average plastic strain ratio r _m and a low in-plane anisotropy Δr, non-aging property, and excellent resistance to surface roughening. Is required.

  Conventional cold-rolled steel sheets for drawn cans are, for example, Japanese Patent No. 3516813 (Patent Document 1), Japanese Patent No. 3996754 (Patent Document 2), Japanese Patent No. 4374126 (Patent Document 3) and Japanese Patent No. 5359709 (Patent Document 4). Is disclosed in.

  The steel sheet for a drawn can disclosed in Patent Document 1 has C: ≤ 0.0030 wt%, Si: ≤ 0.05 wt%, Mn: ≤ 0.5 wt%, P: ≤ 0.03 wt%, S: ≤ 0. 020 wt%, solAl: 0.01 to 0.100 wt%, N: ≦0.0070 wt%, Ti: 0.01 to 0.050 wt%, Nb: 0.008 to 0.030 wt%, B: 0.0002 to The composition is 0.0007 wt% with the balance being Fe and unavoidable elements, and the grain size No. Is 10.0 or more and HR30T is 47 to 57. Patent Document 1 describes that the steel sheet for a drawn can can suppress surface defects.

  The steel plate for a drawn can disclosed in Patent Document 2 has C: 0.0050 to 0.0170%, Si: ≤ 0.35%, Mn: ≤ 1.0%, P: ≤ 0.020%, S: ≦0.025%, solAl: 0.005 to 0.100%, N: ≦0.0070%, Ti: (6 to 20)×C%, the balance being Fe and inevitable elements, and the Δr value is +0. .15 to −0.12, average r value ≧1.20, GS.no of recrystallized grains is 8.5 to 11.0, and earring ratio is 1.0% or less. ..

  The steel plate for a drawn can disclosed in Patent Document 3 has C: 0.045 to 0.100%, Si: ≤ 0.35%, Mn: ≤ 1.0%, and P: ≤ 0.070 in mass%. %, S: ≤ 0.025%, solAl: 0.005 to 0.100%, N: ≤ 0.0060%, B: B/N = 0.5 to 2.5, balance Fe and unavoidable impurities A steel sheet having a composition of 0.1 to 0.60 mm, a Δr value of +0.15 to −0.08, and a heating rate of 5° C./sec or more during recrystallization annealing. The crystal orientation of is randomized. Patent Document 3 describes that the steel sheet for a drawn can is particularly excellent in earring property.

  The steel plate for a drawn can disclosed in Patent Document 4 is C: 0.0035 to 0.0080%, Si: ≤ 0.35%, Mn: ≤ 1.0%, P: ≤ 0.030 in mass%. %, S: ≤ 0.025%, solAl: 0.003 to 0.100%, N: ≤ 0.0100%, Nb ≤ 0.040% and (3 to 6) x C%, the balance being Fe and The composition of unavoidable impurities has a Δr value of +0.15 to −0.15, an average r value of 1.00 to 1.35, and GS. No.: 11.0 to 13.0, earring ratio: 2.5% or less. Patent Document 4 describes that the steel sheet for a drawn can is excellent in earring property and surface quality after drawing.

Japanese Patent No. 3516813 Japanese Patent No. 3996754 Japanese Patent No. 4374126 Japanese Patent No. 5359709

However, the grain size number of the cold rolled steel sheet of Patent Document 1 is 10.3 to 10.9 (see Table 2 of Patent Document 1), and the grain size number of the cold rolled steel sheet of Patent Document 2 is 8.8 to 10.8. (See Table 2 of Patent Document 2), and each has a large particle size. Further, although Patent Document 3 discloses a steel plate for a squeezing can having excellent earring properties, it does not disclose a grain size number. Further, since it is a low carbon steel, the average plastic strain ratio r _m is estimated to be a low value of about 1.0. The grain size number of the cold rolled steel sheet of Patent Document 4 is 11.6 to 12.1 (see Table 2 of Patent Document 4) and the grain size is small, but the average r value is 1.05 to 1.35 (Patent Document 4). 4 (see Table 2). Therefore, the steel sheets disclosed in these documents may have low surface roughening resistance and drawability of the can. As described above, it was difficult to obtain a steel sheet having both press formability (drawing workability) and surface roughening resistance, as well as good earring property and non-aging property, by the conventional technique.

  An object of the present invention is to provide a cold-rolled steel sheet for a drawn can which is excellent in drawability and resistance to surface roughening of the can.

The cold-rolled steel sheet for a squeezing can of the present embodiment is, in mass %, C: 0.0060 to 0.0110%, Si: 0.50% or less, Mn: 0.70% or less, P: 0.070% or less. , S: 0.05% or less, Sol. Al: 0.005 to 0.100%, N: 0.0025 to 0.0080%, Nb satisfying the formula (1), and B: 0 to 0.0030% are contained, and the balance is Fe and impurities. And a ferrite single phase structure having a grain size number of 11.0 or more, a plate thickness of 0.15 to 0.50 mm, and an aging treatment at 100° C. for 1 hour. In the L direction of the cold rolled steel sheet for drawn cans, the yield point strength YP is 220 to 290 MPa, the tensile strength TS is 330 to 390 MPa, the total elongation EL is 32% or more, the yield point elongation YP-EL is 0%, and the average plasticity is The strain ratio r _m exceeds 1.35, and the in-plane anisotropy Δr is −0.30 to +0.15.
440C+2.2≦Nb/C≦440C+5.2 (1)
Here, the content (mass %) of the corresponding element is substituted for the element symbol in the formula (1).

  The fine-grain cold-rolled steel sheet for drawn cans according to the present embodiment is excellent in drawability and resistance to surface roughening of the cans.

FIG. 1 is a diagram showing the relationship between the C content and F1 (=Nb/C) and the material characteristics. FIG. 2 is a diagram showing the relationship between the N content and the in-plane anisotropy Δr.

  The present inventors investigated and examined the drawability and the rough skin resistance of cans, and obtained the following findings.

  Roughness generated on the surface of the cold rolled steel sheet after can making can be suppressed as the crystal grains of the cold rolled steel sheet before can making become finer. If the crystal grains are fine, the in-plane anisotropy Δr also becomes low.

  As described above, in the cold-rolled steel sheet for drawn cans, it is necessary to suppress the occurrence of stretcher strain during drawing. Stretcher strain occurs due to the Cottrell effect when excess solid solution C is present in the steel. Specifically, when an external force acts on the cold-rolled steel sheet, dislocations do not move to the yield point due to the Cottrell effect due to solid solution C, and dislocations are released from solid solution C at a stretch at the yield point and move. Yield point elongation (YP-EL) occurs. At this time, stretcher strain occurs.

In order to improve the drawability and the surface roughening resistance while suppressing the occurrence of stretcher strain, in the cold rolled steel sheet having a ferrite single-phase structure, the C content is 0.0060 to 0.0110%, and Nb The content is an amount that satisfies the formula (1).
440C+2.2≦Nb/C≦440C+5.2 (1)
Here, the content (mass %) of the corresponding element is substituted for the element symbol in the formula (1).

  Define F1=Nb/C. F1 is an index relating to the amount of C solid solution and the refining of ferrite grains due to Nb carbide.

  If F1 is lower than 440C+2.2, the Nb content relative to the C content in the steel is too small. In this case, the amount of C that remains in solid solution in the steel without being precipitated as NbC (the amount of solid solution C) becomes excessively large. Therefore, due to the Cottrell effect of the solid solution C, the yield point elongation YP-EL occurs, which causes stretcher strain.

  On the other hand, if F1 is higher than 440C+5.2, the Nb content is too high relative to the C content. In this case, NbC is coarsened and the pinning effect is reduced. Therefore, the ferrite grains become coarse and the grain size number becomes less than 11.0. In this case, the in-plane anisotropy Δr becomes high.

  When F1 satisfies the formula (1), an appropriate amount of Nb carbide is generated to make the ferrite grains fine, and the grain size number becomes 11.0 or more. Therefore, the rough skin resistance is enhanced. Further, since the amount of solute C is reduced, stretcher strain does not occur. Further, the ferrite grains are miniaturized, and the in-plane anisotropy Δr can be suppressed low.

FIG. 1 is a diagram showing the relationship between the C content and F1 (=Nb/C) and the material characteristics. FIG. 1 shows the relationship between the C content and F1 and the material properties of the examples described in detail below, in which the components other than C content and Nb/C and the manufacturing conditions are within the scope of the present invention. Is. Regarding the material characteristics, the grain size number is 11.0 or more, the yield point strength YP is 220 to 290 MPa, and the tensile strength is 220 to 290 MPa in the L direction of the cold-rolled steel sheet for drawn cans after aging treatment at 100° C. for 1 hour. The strength TS is 330 to 390 MPa, the total elongation EL is 32% or more, the yield point elongation YP-EL is 0%, the average plastic strain ratio r _m is more than 1.35, and the in-plane anisotropy Δr is −0. Those with a value of 0.30 to +0.15 were accepted, and if any of the above-mentioned material characteristics was deviated, it was rejected.

  From FIG. 1, after limiting the components other than C content and F1 (=Nb/C) and the manufacturing conditions to the scope of the present invention, the C content is set to 0.0060 to 0.010%, and F1 is expressed by the formula ( It is clear that the required material characteristics can be obtained by satisfying 1).

  Furthermore, the present inventors have made detailed studies on the influence of other elements, and have found that the in-plane anisotropy Δr is greatly influenced by the N content. FIG. 2 is a diagram showing the relationship between the N content and the in-plane anisotropy Δr. FIG. 2 shows the relationship between the N content and the in-plane anisotropy Δr in the examples which will be described later in detail, in which the components other than the N content and the manufacturing conditions are within the scope of the present invention.

From FIG. 2, it can be seen that the larger the N content, the closer the Δr value is to 0, and the in-plane anisotropy Δr improves. However, if excessively large N content, the average plastic strain ratio r _m is decreased, the proper value of N amount was found that a 0.0025 to 0.0080%.

The cold-rolled steel sheet for a drawn can of this embodiment completed based on the above findings is C: 0.0060 to 0.0110%, Si: 0.50% or less, Mn: 0.70% or less, and P in mass %. : 0.070% or less, S: 0.05% or less, Sol. Al: 0.005 to 0.100%, N: 0.0025 to 0.0080%, Nb satisfying the formula (1), and B: 0 to 0.0030% are contained, and the balance is Fe and impurities. And a ferrite single phase structure having a grain size number of 11.0 or more, a plate thickness of 0.15 to 0.50 mm, and an aging treatment at 100° C. for 1 hour. In the L direction of the cold rolled steel sheet for drawn cans, the yield point strength YP is 220 to 290 MPa, the tensile strength TS is 330 to 390 MPa, the total elongation EL is 32% or more, the yield point elongation YP-EL is 0%, and the average plasticity is The strain ratio r _m exceeds 1.35, and the in-plane anisotropy Δr is −0.30 to +0.15.
440C+2.2≦Nb/C≦440C+5.2 (1)
Here, the content (mass %) of the corresponding element is substituted for the element symbol in the formula (1).

  The cold-rolled steel sheet for a drawn can may further include any one of a Ni plating layer, a Ni diffusion plating layer, a Sn plating layer, and a tin-free steel (TFS) plating layer on the surface.

  In the method for manufacturing a cold-rolled steel sheet for a drawn can according to the present embodiment, a slab having the above chemical composition is heated to 1000° C. or higher, finish rolling is performed at 870 to 960° C., and after finish rolling, cooling is performed to 450 to 700. Winding at less than °C, a step of producing a hot rolled steel sheet, a step of performing cold rolling on the hot rolled steel sheet, and producing a cold rolled steel sheet having a sheet thickness of 0.15 to 0.50 mm, The cold-rolled steel sheet is soaked at 740 to 800° C. and then subjected to continuous annealing for cooling, and a step of temper rolling the cooled cold-rolled steel sheet at a rolling reduction of 0.5 to 5.0%.

  In the step of producing the hot rolled steel sheet, the slab may be heated at 1100 to 1230°C and wound at 600 to 670°C to produce the hot rolled steel sheet.

  In the manufacturing method, after performing the heat treatment step, at least one surface of the cold-rolled steel sheet may be subjected to any one of Ni plating treatment, Sn plating treatment, and TFS plating treatment.

  The above-mentioned manufacturing method may further carry out Ni plating treatment on at least one surface of the cold-rolled steel sheet after the step of producing the cold-rolled steel sheet and before the step of carrying out the continuous annealing.

  Hereinafter, the cold-rolled steel sheet for a drawn can of this embodiment will be described in detail.

[Chemical composition]
The chemical composition of the cold-rolled steel sheet for drawn cans of the present embodiment contains the following elements.

C: 0.0060 to 0.0110%
Carbon (C) forms a solid solution to increase the strength of steel. If the C content is 0.0060% or more, the yield strength YP in the L direction after accelerated aging treatment is 220 MPa or more and the tensile strength TS is 330 MPa, provided that the other chemical composition and manufacturing conditions described later are satisfied. That is all. If the C content is less than 0.0060%, this effect cannot be obtained. On the other hand, if the C content exceeds 0.0110%, the hardness of the cold rolled steel sheet becomes too high. In this case, the total elongation EL in the L direction after the accelerated aging treatment is reduced, and the drawability is reduced. Therefore, the C content is 0.0060 to 0.0110%. The preferable lower limit of the C content is 0.0065%, and more preferably 0.0070%. The preferable upper limit of the C content is 0.0105%.

Si: 0.50% or less Silicon (Si) is an impurity that is inevitably contained in the cold rolled steel sheet of the present embodiment. Si reduces the plating adhesion of the cold-rolled steel sheet and the coating adhesion of the cold-rolled steel sheet after can making. Therefore, the Si content is 0.50% or less. The preferable upper limit of the Si content is less than 0.50%. The Si content is preferably as low as possible.

Mn: 0.70% or less Manganese (Mn) is an impurity that is inevitably contained in the cold-rolled steel sheet of the present embodiment. Mn hardens the cold rolled steel sheet and reduces the total elongation EL of the cold rolled steel sheet. Therefore, press formability (drawability) is reduced. Therefore, the Mn content is 0.70% or less. The preferable upper limit of the Mn content is less than 0.70%. It is preferable that the Mn content is as low as possible.

P: 0.070% or less Phosphorus (P) is inevitably contained. P enhances the strength of the cold rolled steel sheet. However, if the P content is too high, the press formability is reduced. Specifically, the secondary work brittleness cracking resistance of the can is reduced. In a deep-drawn can, for example, at a low temperature such as −10° C., the side wall end portion of the can may be brittlely fractured due to impact at the time of dropping or bending strain. Such easiness of fracture is called secondary work brittle crack. Excessive inclusion of P easily causes secondary work brittle cracking. Therefore, the P content is 0.070% or less.

S: 0.05% or less Sulfur (S) is an impurity. S causes brittle cracks in the surface layer of the steel sheet during hot rolling, and rough edges of the hot rolled steel strip. Therefore, the S content is 0.05% or less. It is preferable that the S content is as low as possible.

Sol. Al: 0.005-0.100%
Aluminum (Al) deoxidizes steel during slab manufacturing. If the Al content is less than 0.005%, the above effect cannot be obtained. On the other hand, if the Al content exceeds 0.100%, the above effect is saturated and the manufacturing cost becomes high. Therefore, the Al content is 0.005 to 0.100%. In the present specification, the Al content is the content of acid-soluble Al (Sol.Al).

N: 0.0025 to 0.0080%
Nitrogen (N) reduces the in-plane anisotropy Δr of steel. If the N content is less than 0.0025%, the in-plane anisotropy becomes large and the earring property deteriorates. On the other hand, N content if it exceeds 0.0080%, and the average plastic strain ratio r _m is reduced. Therefore, the N content is 0.0025 to 0.0080%. The preferable lower limit of the N content is 0.0030%, and more preferably 0.0045%. The preferable upper limit of the N content is 0.0070%, and more preferably 0.0065%.

Nb: Content satisfying formula (1) 440×C+2.2≦Nb/C≦440×C+5.2 (1)
Here, the content (mass %) of the corresponding element is substituted for the element symbol in the formula (1).

  Nb forms fine carbides, suppresses the amount of solid solution C, and refines the crystal grains. It is defined as F1=Nb/C. F1 is an index relating to the refinement of ferrite grains by Nb carbide. If F1 is lower than 440C+2.2, the Nb content relative to the C content in the steel is too small. In this case, the amount of C that remains in solid solution in the steel without being precipitated as NbC (the amount of solid solution C) increases. Therefore, due to the Cottrell effect of solute C, elongation at yield YP-EL occurs. On the other hand, if F1 is higher than 440C+5.2, the Nb content is too high relative to the C content. In this case, NbC is coarsened and the pinning effect is reduced. Therefore, the ferrite grains become coarse and the grain size number becomes less than 11.0. In this case, rough skin may occur. Further, the in-plane anisotropy Δr becomes large and the drawability deteriorates.

  When F1 is 440C+2.2 to 440C+5.2, the Nb content relative to the C content in the steel is appropriate. In this case, fine NbC is sufficiently precipitated. Due to the pinning effect of these fine NbC, the ferrite grains are refined, and the grain size number becomes 11.0 or more. Further, since the amount of dissolved C is suppressed, the yield point elongation YP-EL does not occur (YP-EL=0%). Therefore, the trecher strain does not occur.

  The balance of the chemical composition of the cold-rolled steel sheet for drawn cans of this embodiment is Fe and impurities. In the present specification, an impurity means an ore as a raw material, a scrap, or a contaminant mixed in from a manufacturing environment or the like when industrially manufacturing a steel material. The impurities are, for example, Cu, Ni, Cr and Sn. The preferred contents of these elements are Cu: 0.5% or less, Ni: 0.5% or less, Cr: 0.3% or less, and Sn: 0.05% or less.

  The cold-rolled steel sheet for drawn cans may further contain B in its chemical composition.

B: 0 to 0.0030%
Boron (B) is an optional element and may not be contained. When included, B refines the recrystallized grains during annealing. However, if the B content exceeds 0.0030%, the optimum cold rolling rate due to grain refinement decreases, and the productivity decreases. Therefore, the B content is 0.0030%. The preferable lower limit of the B content is 0.0001%, and more preferably 0.0003%. The preferable upper limit of the B content is 0.0020%.

[Microstructure and grain size number]
The microstructure of the cold-rolled steel sheet of this embodiment is composed of ferrite and inclusions and/or precipitates. That is, the matrix (matrix) of the microstructure is a ferrite single phase. Since the matrix is a single ferrite phase, uniform deformation can be realized and the total elongation EL can be 30% or more. Therefore, excellent deep drawing workability can be obtained.

  Further, the grain size number of the ferrite grains is 11.0 or more. If the crystal grains are large, rough skin is likely to occur. In addition, the in-plane anisotropy Δr becomes large and the earring property deteriorates. When the grain size number is 11.0 or more, the can has excellent resistance to surface roughening, and the in-plane anisotropy Δr is −0.30 to +0.15, which is excellent in earring property. The grain size number of the ferrite grains of the cold rolled steel sheet of this embodiment is preferably 11.2 or more.

  The crystal grain size number of ferrite grains in the present specification means the crystal grain size number according to JIS G 0551 (2013). Specifically, the grain size number is measured by the comparison method (see 7.2 of the same standard).

[Mechanical properties]
Yield point strength YP, total elongation EL, yield point elongation YP in the L direction after aging treatment (hereinafter referred to as accelerated aging treatment) for 1 hour at 100° C. on the cold-rolled steel sheet for drawn cans described above. -EL, average plastic strain ratio r _m values, the in-plane anisotropy Δr is as follows.
YP: 220-290 MPa,
TS: 330-390 MPa,
El≧30%
YP-El≦0
Average plastic strain ratio r _m >1.35
In-plane anisotropy Δr: −0.30 to +0.15
The average plastic strain ratio r _m of the cold-rolled steel sheet for the drawn can this embodiment preferably is 1.40 or more.

  Here, the yield strength YP in the L direction, the total elongation EL, and the yield point elongation YP-EL are obtained by the following method. A JIS No. 5 tensile test piece whose parallel part is parallel to the L direction (rolling direction) is prepared from a cold-rolled steel sheet for drawn cans. The manufactured test piece is subjected to an aging treatment (accelerated aging treatment) at 100° C. for 1 hour. The tensile test piece after the accelerated aging treatment was subjected to a tensile test in the air at room temperature (25° C.) in accordance with JIS Z 2241 (2011), and yield strength YP (MPa), tensile strength TS (MPa) and total elongation EL (%) are calculated.

The average plastic strain ratio r _m and the in-plane anisotropy Δr are obtained by the following method. A plastic strain ratio test according to JIS Z 2254 (2008) was performed on the cold rolled steel sheet for drawn cans, and the average plastic strain ratio r _m and the in-plane anisotropy Δr when the plastic strain amount was 15% were measured. Ask.

[Production method]
An example of the method for manufacturing the cold-rolled steel sheet for drawn cans of this embodiment will be described. The manufacturing method of the present embodiment includes a step of manufacturing a slab (steel making step), a step of manufacturing a hot rolled steel sheet (hot rolling step), a step of manufacturing a cold rolled steel sheet (cold rolling step), and a cold rolling step. The method includes a step of performing CAL (continuous annealing) on the steel sheet (CAL step) and a step of performing temper rolling on the cold rolled steel sheet after CAL (temper rolling step). Hereinafter, each step will be described in detail.

[Steel making process]
First, molten steel having the above chemical composition is manufactured. A slab (slab) is manufactured from the manufactured molten steel by a continuous casting method.

[Hot rolling process]
The slab heated at a heating temperature of 1000° C. or higher is hot-rolled under the normally hot-rolling condition to produce a hot-rolled steel sheet. More specifically, the heating temperature of the slab is, for example, 1000°C to 1280°C. When the heating temperature of the slab exceeds 1280°C, ear cracks are likely to occur during hot rolling. In addition, the average plastic strain ratio r _m decreases. When the heating temperature of the slab becomes lower than 1000°C, it becomes difficult to secure an appropriate finish rolling temperature. The preferable heating temperature of the slab is 1100°C to 1230°C. In hot rolling, for example, finish rolling is performed at a finish rolling temperature FT of 870 to 960°C. When the FT exceeds 960°C, the average plastic strain ratio r _m decreases, and when the FT becomes lower than 870°C, the in-plane anisotropy Δr increases. The hot-rolled steel sheet after finish rolling is cooled in a cooling zone and then wound around a coil. The winding temperature CT is, for example, 450 to less than 700°C. CT is the cold rolling and after annealing the crystal grains coarse exceeds 700 ° C., the CT is lower than 450 ° C., an average plastic strain ratio r _m becomes large in-plane anisotropy Δr with reduced. A preferable winding temperature CT is 600 to 670°C.

[Cold rolling process]
The hot rolled steel sheet is cold rolled to produce a cold rolled steel sheet. The cold rolling may be performed by a known method. Preferably, the cold rolling rate is preferably changed in advance to study the optimum cold rolling rate of the cold rolled steel sheet for drawing cans, and the cold rolling rate is set so that the in-plane anisotropy Δr of the steel sheet becomes small. To do. If the cold rolling rate is less than 80% or more than 90%, the in-plane anisotropy of the steel sheet increases. Therefore, the cold rolling rate is preferably 80% or more and less than 90%.

[CAL (continuous annealing) step]
Continuous annealing is performed on the cold rolled steel sheet. Since the continuous annealing line is referred to as "Continuous Annealing Line", the continuous annealing is referred to as "CAL" in this specification. The annealing temperature ST in CAL is 740 to 800°C. If the annealing temperature ST is less than 740° C., recrystallization is not completed in the steel and the unrecrystallized structure remains. In this case, desired mechanical characteristics cannot be obtained. On the other hand, if the annealing temperature ST exceeds 800° C., the recrystallized grains become coarse and the grain size number exceeds 11.0. Therefore, the annealing temperature ST is 740 to 800°C. The preferable lower limit of the annealing temperature ST is 760°C. The preferable upper limit of the annealing temperature ST is 780°C. The soaking time at the annealing temperature ST is, for example, 10 to 60 seconds.

[About BAF-OA]
In the present embodiment, the present embodiment is performed without performing overaging treatment (box annealing is “Box Annealing Furnace” and overaging treatment is “Over Aging”, hereinafter referred to as BAF-OA) in box annealing after CAL. In the high-strength cold-rolled steel sheet of the form, the yield point elongation YP-EL after accelerated aging treatment is 0%, and stretcher strain does not occur. Therefore, in this embodiment, BAF-OA is not performed after CAL. Therefore, productivity is increased.

[Temperature rolling process]
Temper rolling (skin pass rolling) is performed on the cold rolled steel sheet after CAL. The rolling reduction in temper rolling is 0.5 to 5.0%. If the rolling reduction is less than 0.5%, yield point elongation YP-EL may occur in the cold rolled steel sheet after the accelerated aging treatment. If the rolling reduction exceeds 5.0%, the total elongation EL will be less than 30%, and the press formability (drawability) will deteriorate. When the rolling reduction is 0.5 to 5.0%, stretcher strain does not occur and excellent press formability (drawing workability) is also obtained.

  Through the above manufacturing process, the cold-rolled steel sheet for a drawn can of this embodiment is manufactured. The plate thickness of the cold-rolled steel sheet for drawn cans is 0.15 to 0.50 mm. If the plate thickness exceeds 0.50 mm, it becomes difficult to obtain excellent drawability. If the sheet thickness is less than 0.15 mm, the sheet thickness of the hot-rolled steel sheet must be reduced, and in this case, the finishing temperature at the time of hot rolling cannot be secured. Therefore, the plate thickness of the cold rolled steel plate is 0.15 to 0.50 mm.

[Plating]
The cold rolling steel sheet for drawn cans may be subjected to plating treatment. The plating treatment is, for example, any one of a Ni plating treatment, a Ni diffusion plating treatment, a Sn plating treatment, and a tin-free steel (TFS) plating treatment. The Ni plating treatment, the Sn plating treatment, and the TFS plating treatment are performed, for example, on the cold rolled steel sheet after the temper rolling step.

When carrying out the Ni plating treatment, the preferable thickness of the Ni plating layer formed on the surface of the cold-rolled steel sheet is 0.5 to 5.0 μm (the amount of Ni deposited is 4.45 to 44.5 g/m ² ). Is.

  When carrying out the Ni diffusion plating treatment, the Ni plating treatment is carried out after the cold rolling step and before the CAL step. In this case, CAL is performed on the cold-rolled steel sheet on which the Ni plating layer is formed. During CAL, Ni in the Ni plating layer diffuses to form a Ni diffusion plating layer.

  Cold-rolled steel sheets with various chemical compositions were manufactured under various manufacturing conditions and investigated for mechanical properties and r-values.

[Method of manufacturing test material]
Slabs of steels A to Q having the chemical compositions shown in Table 1 were manufactured.

  The slab of each test number was hot-rolled under the hot-rolling conditions (slab heating temperature (°C), finish rolling temperature FT (°C), winding temperature CT (°C)) shown in Table 2 to obtain a hot-rolled steel sheet. Was manufactured.

  After pickling the hot rolled steel sheet, cold rolling was carried out under the cold rolling conditions (cold rolling rate) shown in Table 2 to produce a cold rolled steel sheet having a plate thickness of 0.25 mm. The cold-rolled steel sheet of test number 4 was subjected to Ni diffusion plating treatment. Specifically, before CAL, a Ni plating film was formed on the front and back surfaces of the cold rolled steel sheet by an electroplating method. The thickness of the Ni plating film on each of the front surface and the back surface was 2 μm. No plating treatment was performed on cold-rolled steel sheets with test numbers other than the test number 4.

  CAL (continuous annealing) was performed on the obtained cold rolled steel sheet. The annealing temperature ST (°C) was as shown in Table 2. The cold rolled steel sheet of each test number was soaked at the annealing temperature ST (°C) for 25 seconds. Then, gas cooling with nitrogen gas was performed. In gas cooling, the average cooling rate from the annealing temperature ST (° C.) to 50° C. or lower was 25° C./sec in all cases.

  For the cold rolled steel sheet of test number 8, BAF-OA was further performed after CAL. In BAF-OA, the cold rolled steel sheet was soaked at 450° C. for 5 hours and then gradually cooled for 72 hours. BAF-OA was not performed on the cold-rolled steel sheets with other test numbers. In the "annealing method" column in Table 2, "CAL+BAF-OA" indicates that BAF-OA was performed after CAL. “CAL” indicates that CAL was performed and BAF-OA was not performed.

  Temper rolling was performed on the cold rolled steel sheet after annealing. The rolling reductions in temper rolling were all 1.8%. Through the above manufacturing process, a cold-rolled steel sheet as a test material was manufactured.

[Test method]
[Observation of microstructure and measurement of grain size number]
An optical microscope observation was performed on the L cross section of the cold rolled steel sheet after the temper rolling was performed, and the structure of the cold rolled steel sheet was specified. The identified results are shown in Table 2. All the microstructures were ferrite single-phase structures. Further, the crystal grain size number of the ferrite grains of the cold rolled steel sheet of each test number was determined by the above-mentioned method according to JIS G 0552 (2013). The results obtained are shown in Table 2.

[Mechanical property evaluation test]
JIS No. 5 tensile test pieces were prepared from cold-rolled steel sheets of each test number. The parallel part of the tensile test piece was parallel to the L direction (rolling direction) of the cold rolled steel sheet. An accelerated aging treatment was performed on the manufactured tensile test piece. Specifically, each tensile test piece was subjected to an aging treatment at 100° C. for 1 hour.

  A tensile test is performed on the tensile test piece after the accelerated aging treatment in accordance with JIS Z 2241 (2011) in the air at room temperature (25° C.) to yield strength YP (MPa) and tensile strength TS. (MPa), total elongation EL (%) and yield point elongation YP-EL (%) were determined. The obtained results are shown in Table 2.

[R _m value and Δr value measurement test]
A plastic strain ratio test according to JIS Z 2254 (2008) was carried out on the cold rolled steel sheet of each test number, and the average plastic strain ratio r _m and the in-plane anisotropy Δr when the plastic strain amount was 15%. I asked. The obtained results are shown in Table 2.

[Test results]
With reference to Table 2, the chemical compositions of test numbers 1 to 6 were appropriate, and F1 was also within the range of formula (1). Furthermore, the manufacturing conditions were also appropriate. Therefore, in the cold-rolled steel sheets of these test numbers, the grain size number was as high as 11.0 or more, and the ferrite grains were fine. Therefore, the average plastic strain ratio r _m was over 1.35, the in-plane anisotropy Δr was −0.30 to +0.15, and the press formability and the surface roughening resistance were high.

  Further, in any of the test numbers, in the L direction of the cold rolled steel sheet after the accelerated aging treatment, the yield point strength YP is 220 to 290 MPa, the tensile strength TS is 330 to 390 MPa, the total elongation EL is 32% or more, and the yield point elongation is 32% or more. YP-EL was 0%, and excellent mechanical properties were obtained.

On the other hand, in test number 7, the C content was too high and the N content was too low. Further, in the annealing step, CAL and BAF-OA were carried out, and the annealing temperature ST was also low at less than 740°C. As a result, the average plastic strain ratio r _m was as low as 1.35 or less, and the press formability was low.

  In test number 8, the C content was too low. As a result, the grain size number was less than 11.0, and the surface roughening resistance was low. Further, the yield strength was low, less than 220 MPa. Further, the in-plane anisotropy Δr was lower than −0.30, and the press formability was low.

  In test number 9, F1 was less than the lower limit of formula (1). Therefore, the yield point elongation YP-EL was higher than 0% and stretcher strain occurred.

  In test number 10, F1 exceeded the upper limit of formula (1). Therefore, the grain size number was less than 11.0, and the rough skin resistance was low. Further, the in-plane anisotropy Δr was lower than −0.30, and the press formability was low.

  In test number 11, F1 was less than the lower limit of formula (1). Therefore, the yield point elongation YP-EL was higher than 0% and stretcher strain occurred. Further, the yield point strength YP exceeded 390 MPa and the total elongation EL was less than 32%. It is considered that since F1 was less than the lower limit of the formula (1) and the amount of solute C was excessively large, stretcher strain was generated and the strength was excessively high, and as a result, the total elongation EL was low.

  In test number 12, the C content was too high. Therefore, the grain size number was less than 11.0, and the rough skin resistance was low. Further, the in-plane anisotropy Δr was lower than −0.30, and the press formability was low.

  In test number 13, the N content was too low. Therefore, the in-plane anisotropy Δr was lower than −0.30, and the press formability was low.

In test number 14, the N content was too high. Therefore, the average plastic strain ratio r _m was as low as 1.35 or less, and the press formability was low. In addition, the grain size number was less than 11.0, and the rough skin resistance was low.

  In test number 15, F1 exceeded the upper limit of formula (1). Therefore, the grain size number was less than 11.0, and the rough skin resistance was low. Further, the in-plane anisotropy Δr was lower than −0.30, and the press formability was low.

  In test number 16, F1 exceeded the upper limit of formula (1). Therefore, the grain size number was less than 11.0, and the rough skin resistance was low. Further, the in-plane anisotropy Δr was lower than −0.30, and the press formability was low.

  In test number 17, F1 was less than the lower limit of formula (1). Therefore, the yield point elongation YP-EL was higher than 0% and stretcher strain occurred.

In test number 18, the annealing temperature ST was too low. Therefore, the average plastic strain ratio r _m was as low as 1.35 or less, the in-plane anisotropy Δr was lower than −0.30, and the press formability was low. Further, the yield point strength YP was higher than 280 MPa and the tensile strength TS was also higher than 390 MPa.

  In test number 19, the annealing temperature ST was too high. Therefore, the grain size number was less than 11.0, and the rough skin resistance was low.

In the test number 20, the hot rolling finish temperature FT was too high. Therefore, the average plastic strain ratio r _m was as low as 1.35 or less, and the press formability was low.

  In the test number 21, the hot rolling finish temperature FT was too low. Therefore, the in-plane anisotropy Δr was lower than −0.30, and the press formability was low.

  In the test number 22, the hot rolling coiling temperature CT was too high. Therefore, the grain size number was less than 11.0, and the rough skin resistance was low.

In the test number 23, the hot rolling coiling temperature CT was too low. Therefore, the average plastic strain ratio r _m was as low as 1.35 or less, the in-plane anisotropy Δr was lower than −0.30, and the press formability was low. Furthermore, the tensile strength TS exceeded 390 MPa.

In test number 24, the slab heating temperature was too high. Therefore, the grain size number was less than 11.0, and the rough skin resistance was low. Furthermore, the average plastic strain ratio r _m was as low as 1.35 or less, and the press formability was low.

  The embodiments of the present invention have been described above. However, the embodiments described above are merely examples for implementing the present invention. Therefore, the present invention is not limited to the above-described embodiments, and can be implemented by appropriately modifying the above-described embodiments without departing from the spirit thereof.

Claims (6)

A cold-rolled steel sheet for drawn cans,
In mass %,
C: 0.0060 to 0.0110%,
Si: 0.50% or less,
Mn: 0.70% or less,
P: 0.070% or less,
S: 0.05% or less,
Sol. Al: 0.005 to 0.100%,
N: 0.0025 to 0.0080%,
Nb that satisfies Expression (1), and
B:0-0.0030% is contained, the balance is a chemical composition consisting of Fe and impurities,
And a ferrite single-phase structure having a grain size number of 11.0 or more,
The plate thickness is 0.15 to 0.50 mm,
In the L direction of the cold-rolled steel sheet for drawn cans after performing the aging treatment at 100° C. for 1 hour, the yield point strength YP is 220 to 290 MPa, the tensile strength TS is 330 to 390 MPa, and the total elongation EL is 32% or more. Yield point elongation YP-EL is 0%,
The average plastic strain ratio _{r m} is 1.35 greater, and in-plane anisotropy Δr is -0.30～ + 0.15, cold-rolled steel sheet for drawn can.
440C+2.2≦Nb/C≦440C+5.2 (1)
Here, the content (mass %) of the corresponding element is substituted for the element symbol in the formula (1). The cold-rolled steel sheet for drawn cans according to claim 1, further comprising:
A cold-rolled steel sheet for a drawn can, which is provided with any one of a Ni plating layer, a Ni diffusion plating layer, a Sn plating layer, and a tin-free steel (TFS) plating layer on its surface. A method of manufacturing a cold-rolled steel sheet for a drawn can according to claim 1,
A slab having the chemical composition according to claim 1 is heated to 1000 to 1280° C., finish rolling is performed at 870 to 960° C., finish rolling is followed by cooling and winding at 450 to less than 700° C., hot rolled steel sheet. A process of manufacturing
Cold rolling the hot rolled steel sheet to produce a cold rolled steel sheet having a thickness of 0.15 to 0.50 mm;
A step of soaking the cold rolled steel sheet at 740 to 800° C., and then performing continuous annealing for cooling;
A method for producing a cold-rolled steel sheet for a drawing can, comprising a step of temper-rolling the cooled cold-rolled steel sheet at a rolling reduction of 0.5 to 5.0%. It is a manufacturing method of the cold-rolled steel sheet for drawn cans of Claim 3, Comprising:
In the step of producing the hot-rolled steel sheet, the method for producing a cold-rolled steel sheet for drawing cans, wherein the slab is heated at 1100 to 1230°C and wound at 600 to 670°C to produce the hot-rolled steel sheet. A method for manufacturing a cold-rolled steel sheet for a drawn can according to claim 3 or 4, further comprising:
After performing the temper rolling step, at least one surface of the cold rolled steel sheet is subjected to any one of Ni plating treatment, Sn plating treatment, and tin-free steel (TFS) plating treatment. Manufacturing method of cold rolled steel sheet. A method for manufacturing a cold-rolled steel sheet for a drawn can according to claim 3 or 4, further comprising:
After the step of manufacturing the cold-rolled steel sheet, but before the step of carrying out the continuous annealing, at least one surface of the cold-rolled steel sheet is subjected to Ni plating treatment. Production method.

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