JP2017190469A - Cold-rolled steel sheet for drawn cans and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cold rolled steel sheet for a drawn can excellent in deep drawability and surface roughening resistance.SOLUTION: The cold steel sheet for a drawn can is provided that has a chemical composition containing, by 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 and B satisfying the formula (1):0 to 0.0030% and the balance Fe with impurities and has a ferrite single phase structure with crystal grain size number of 11.0 or more. After the cold steel sheet for a drawn can is subjected to an aging treatment at 100°C for 1 hour, the cold steel sheet has a yield point strength in an L direction of 220 to 290 MPa, a tensile strength of 330 to 390 MPa, a total elongation of 32% or more, a yield point elongation of 0%, an average plastic strain ratio of over 1.35 and a plane anisotropy of -0.30 to +0.15. 440C+2.2≤Nb/C≤440C+5.2 (1), where element symbols is substituted by content (mass%) of the corresponding element.SELECTED DRAWING: Figure 1

Description

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

  Battery cans such as single to single batteries, button batteries, large hybrid batteries, and various types of containers, such as cold-rolled steel sheets or steel plates, Ni plating, Ni diffusion plating, Sn plating, and tin-free steel (TFS) plating ( A galvanized steel sheet (hereinafter referred to as a cold-rolled steel sheet) subjected to various types of plating such as a metal Cr layer and a Cr hydrated oxide layer) is subjected to severe multistage drawing and DI (Drawing and Ironing: Manufactured by carrying out processing such as drawing and ironing. Alternatively, after making a cold-rolled steel plate, various plating or coatings such as Ni plating, Sn plating, TFS plating and the like are applied to form a can container.

  The main characteristics required for the cold-rolled steel sheet used in these cans are (1) press formability (mould be formed without defects such as cracks during processing), (2) rough skin resistance ( (3) Earring properties (small material anisotropy and small earing after deep drawing), (4) Non-aging (stretcher strain during drawing) That does not occur).

Press formability is general (1), the average plastic strain ratio r _m (hereinafter, the average r value and that there is referred) it is known that good characteristics higher is obtained, Nb added ultra low carbon steel This can be achieved by using IF (Interstitial Free) steel represented by (Nb-SULC). However, in general, the grain of IF steel is coarser than that of low carbon steel. Therefore, in order to increase the average r value, it is necessary to increase the temperature during annealing and further coarsen the crystal grains.

The rough skin resistance of (2) improves as the crystal grains are refined. However, in applications such as battery cans, it is necessary to ensure the sealing property of the sealing part of the upper lid, and therefore, surface quality after drawing that is much better than before is required, and the crystal grain size number is 11.0 or more (average) (Crystal grain size ≦ 7.8 μm). The rough skin resistance worsens as the crystal grains become larger. Therefore, it is difficult to achieve both press formability and rough skin resistance using IF steel with large crystal grains. On the other hand, can be fine crystal grains by using the low-carbon steel, it is difficult to obtain a high average plastic strain ratio r _m. Therefore, it is difficult to achieve both press formability and rough skin resistance even when using low carbon steel.

  The earring property of (3) is better as the in-plane anisotropy Δr value is smaller, and the generation of ears during deep drawing is reduced. If the earrings are good, the steel plate yield associated with the earrings of the drawn can can be improved, and it is possible to reduce problems such as progressive feeding between the processes caused by the earrings in multistage drawing and DI processing, and scratches due to tearing of the earring tips. .

  The non-aging property of (4) is that stretcher strain does not occur during drawing. If stretcher strain occurs, irregularities are formed on the peripheral surface and bottom of the can. If the battery can (squeezed can) has such a concavo-convex shape, the contact electrical resistance increases, which is not preferable. In addition, the tension of the can may be reduced, and the internal and external pressure strength of the can may be reduced. . Therefore, the steel sheet for drawn cans is required not to generate stretcher strain after drawing. The stretcher strain is generated due to yield point elongation (YP-EL: elongation amount of steady deformation that proceeds with a deformation resistance smaller than the yield point immediately after yielding) when the steel sheet is deformed. In order to suppress the occurrence of stretcher strain over a long period of time, the yield point elongation after aging treatment must be zero.

On the other hand, battery cans used in hybrid vehicles and the like are increasingly required to improve performance, and steel plates that can withstand more severe pressing are required. In order to improve the performance of the above-described squeezing excellent workability, having a high average plastic strain ratio r _m and low in-plane anisotropy [Delta] r, has a non-aging, excellent cold-rolled steel sheet to surface roughening resistance Is required.

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

  The steel plate for drawn cans disclosed in Patent Document 1 is 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 A composition comprising 0.0007 wt%, the balance being Fe and inevitable elements. Is 10.0 or more, and HR30T is 47-57. Patent Document 1 describes that the steel plate for a drawn can can suppress surface defects.

  The steel plate for drawn cans 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: (6-20) × C%, the balance is Fe and inevitable elements, and 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 rate is 1.0% or less .

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

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

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

However, the crystal 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 crystal 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), all of which have a large particle size. Patent Document 3 discloses a steel plate for a drawing can excellent in earring properties, but does not disclose the crystal grain size number. Further, it is estimated that the average plastic strain ratio r _m since low carbon steel is a low as 1.0. The crystal 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 particle size is small, but the average r value is 1.05 to 1.35 (Patent Document). 4 (see Table 2). Therefore, in the steel plates disclosed in these documents, the can's rough skin resistance and drawing workability may be low. As described above, in the prior art, it has been difficult to obtain a steel sheet that achieves both press formability (drawing workability) and rough skin resistance, and has excellent earring properties and non-aging properties.

  An object of the present invention is to provide a cold-rolled steel sheet for a drawn can which is excellent in drawing workability and the rough skin resistance of the can.

The cold-rolled steel sheet for drawn cans 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%, the balance being 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 after 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 strain ratio r _m is 1.35 greater, and in-plane anisotropy Δr is -0.30～ + 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 drawing workability and rough skin resistance of the can.

FIG. 1 is a diagram showing the relationship between C content and F1 (= Nb / C) and material properties. 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 drawing workability and the rough skin resistance of the can, and obtained the following knowledge.

  Rough skin that occurs on the surface of the cold-rolled steel sheet after canning can be suppressed as the crystal grains of the cold-rolled steel sheet before canning are finer. If the crystal grains are fine, the in-plane anisotropy Δr is further reduced.

  As described above, in cold-rolled steel sheets 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 solute C is present in the steel. Specifically, when an external force is applied to the cold-rolled steel sheet, the dislocation does not move up to the yield point due to the Cottrell effect due to the solid solution C, and the dislocation is released from the solid solution C at the yield point and moves Yield point elongation (YP-EL) occurs. At this time, stretcher strain is generated.

In order to improve the drawing workability and the rough skin resistance while suppressing the occurrence of stretcher strain, the cold rolled steel sheet having a ferrite single phase structure has a C content of 0.0060 to 0.0110%, and Nb Let content be the quantity which satisfy | fills 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 related to the amount of C solid solution and the refinement of ferrite grains by Nb carbide.

  If F1 is lower than 440C + 2.2, the Nb content is too small relative to the C content in the steel. In this case, the amount of C (solid solution C amount) that is not precipitated as NbC but remains in solid solution in the steel increases excessively. Therefore, the yield point elongation YP-EL occurs due to the Cottrell effect of the solute C, and stretcher strain is generated.

  On the other hand, if F1 is higher than 440C + 5.2, there is too much Nb content with respect to C content. In this case, NbC becomes coarse and the pinning effect decreases. For this reason, the ferrite grains become coarse and the crystal grain size number becomes less than 11.0. In this case, the in-plane anisotropy Δr is increased.

  When F1 satisfies the formula (1), an appropriate amount of Nb carbide is generated to refine the ferrite grains, and the grain size number becomes 11.0 or more. Therefore, rough skin resistance increases. Furthermore, since the amount of dissolved C is reduced, stretcher strain does not occur. Furthermore, the ferrite grains are refined, and the in-plane anisotropy Δr is kept low.

FIG. 1 is a diagram showing the relationship between C content and F1 (= Nb / C) and material properties. FIG. 1 is a summary of the relationship between C content and F1 and material properties for the components other than C content and Nb / C and the production conditions in the scope of the present invention. It is. Regarding the material properties, the crystal grain size number is 11.0 or more, the yield point strength YP 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, tensile strength TS is 330～390MPa, total elongation EL is 32% or more, 0% yield point elongation YP-EL, the average plastic strain ratio r _m is 1.35 greater, and in-plane anisotropy Δr is -0 .30 to +0.15 was accepted, and if any of the above material properties was off, it was rejected.

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

  Furthermore, the present inventors have examined in detail the influence of other elements, and have found that the in-plane anisotropy Δr is greatly affected by the N content. FIG. 2 is a diagram showing the relationship between the N content and the in-plane anisotropy Δr. FIG. 2 summarizes the relationship between the N content and the in-plane anisotropy Δr in the examples described later in detail, in which components other than the N content and production conditions are within the scope of the present invention.

From FIG. 2, it can be seen that as the N content increases, the Δr value approaches 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 drawn cans of the present embodiment completed by the above knowledge 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%, the balance being 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 after 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 strain ratio r _m is 1.35 greater, and in-plane anisotropy Δr is -0.30～ + 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 drawn cans 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.

  The manufacturing method of the cold-rolled steel sheet for drawn cans by this embodiment heats the slab which has the said chemical composition to 1000 degreeC or more, implements finish rolling at 870-960 degreeC, cools after finish rolling, and is 450-700. Winding at less than ° C., producing a hot rolled steel sheet, carrying out cold rolling on the hot rolled steel sheet, producing a cold rolled steel sheet having a thickness of 0.15 to 0.50 mm, It comprises a step of soaking the cold-rolled steel sheet at 740 to 800 ° C., and then performing 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 manufacturing the hot-rolled steel sheet, the slab may be heated at 1100 to 1230 ° C. and wound at 600 to 670 ° C. to manufacture a hot-rolled steel sheet.

  The manufacturing method may further perform any one of Ni plating treatment, Sn plating treatment, and TFS plating treatment on at least one surface of the cold-rolled steel sheet after performing the tempering step.

  The manufacturing method may further include performing Ni plating on at least one surface of the cold-rolled steel sheet after the process of manufacturing the cold-rolled steel sheet and before the step of performing the continuous annealing.

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

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

C: 0.0060 to 0.0110%
Carbon (C) is dissolved to increase the strength of the 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, assuming that other chemical compositions and production conditions described later are satisfied. That's it. 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 lowered, and drawing workability is lowered. Therefore, the C content is 0.0060 to 0.0110%. The minimum with preferable C content is 0.0065%, More preferably, it is 0.0070%. A preferable upper limit of the C content is 0.0105%.

Si: 0.50% or less Silicon (Si) is an unavoidable impurity 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 canning. Therefore, the Si content is 0.50% or less. The upper limit with preferable 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 unavoidable impurity in the cold-rolled steel sheet of the present embodiment. Mn hardens the cold-rolled steel sheet and lowers the total elongation EL of the cold-rolled steel sheet. Therefore, press formability (drawing workability) is lowered. Therefore, the Mn content is 0.70% or less. The upper limit with preferable 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 increases the strength of the cold-rolled steel sheet. However, if the P content is too high, the press formability decreases. Specifically, the secondary work brittle crack resistance in the can is reduced. In a deep-drawn can, for example, at a low temperature such as −10 ° C., the end portion of the can side wall may be brittle ruptured due to an impact at the time of dropping or bending distortion. Such ease of breakage is referred to as secondary work brittle cracking. Excessive inclusion of P tends to cause 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 surface brittle cracks in the steel sheet during hot rolling, and causes rough ears in the hot-rolled steel strip. Therefore, the S content is 0.05% or less. The S content is preferably as low as possible.

Sol. Al: 0.005 to 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 increases. Therefore, the Al content is 0.005 to 0.100%. In this 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 the steel. If the N content is less than 0.0025%, the in-plane anisotropy is increased and the earring properties are lowered. 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 minimum with preferable N content is 0.0030%, More preferably, it is 0.0045%. The upper limit with preferable N content is 0.0070%, More preferably, it is 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 dissolved C, and refines crystal grains. Define F1 = Nb / C. F1 is an index related to the refinement of ferrite grains by Nb carbide. If F1 is lower than 440C + 2.2, the Nb content is too small relative to the C content in the steel. In this case, the amount of C that remains as a solid solution in the steel without being precipitated as NbC (the amount of solid solution C) increases. Therefore, the yield point elongation YP-EL occurs due to the Cottrell effect of the solute C. On the other hand, if F1 is higher than 440C + 5.2, there is too much Nb content with respect to C content. In this case, NbC becomes coarse and the pinning effect decreases. For this reason, the ferrite grains become coarse and the crystal grain size number becomes less than 11.0. In this case, rough skin may occur. Further, the in-plane anisotropy Δr is increased, and the drawing processability is lowered.

  If 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 crystal grain size number is 11.0 or more. Furthermore, since the amount of dissolved C is suppressed, yield point elongation YP-EL does not occur (YP-EL = 0%). Therefore, no tretler strain is generated.

  The balance of the chemical composition of the cold-rolled steel sheet for drawn cans of the present embodiment is composed of Fe and impurities. In this specification, an impurity means the thing mixed from the ore as a raw material, a scrap, or a manufacturing environment, etc., when manufacturing steel materials industrially. 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 chemical composition of the cold-rolled steel sheet for drawn cans may further contain B.

B: 0 to 0.0030%
Boron (B) is an optional element and may not be contained. When contained, B refines the recrystallized grains during annealing. However, if the B content exceeds 0.0030%, the optimum cold rolling rate due to fine graining is lowered, and the productivity is lowered. Therefore, the B content is 0.0030%. The minimum with preferable B content is 0.0001%, More preferably, it is 0.0003%. The upper limit with preferable 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 ferrite single phase, uniform deformation can be realized, and the total elongation EL can be 30% or more. Therefore, excellent deep drawing workability can be obtained.

  Furthermore, the crystal grain size number of the ferrite grains is 11.0 or more. If the crystal grains are coarse, rough skin is likely to occur. Further, the in-plane anisotropy Δr is increased, and the earring property is lowered. If the crystal grain size number is 11.0 or more, the skin resistance of the can is excellent, and the in-plane anisotropy Δr is −0.30 to +0.15, and the earrings are also excellent. The grain size number of the ferrite grains of the cold rolled steel sheet of the present embodiment is preferably 11.2 or more.

  The grain size number of the ferrite grain in this specification means the grain size number based on JIS G 0551 (2013). Specifically, the crystal grain size number is measured by measurement by a comparative method (see 7.2 in 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) at 100 ° C. for 1 hour 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 to 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 the present embodiment preferably is 1.40 or more.

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

The average plastic strain ratio r _m and the in-plane anisotropy Δr is obtained by the following method. Against stop cold rolled steel sheet for cans, performed plastic strain ratio test based on JIS Z 2254 (2008), an average plastic strain ratio r _m and the in-plane anisotropy Δr when plastic strain amount is 15% Ask.

[Production method]
An example of the manufacturing method of the cold-rolled steel sheet for drawn cans of this embodiment is demonstrated. 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 plate (hot rolling step), a step of manufacturing a cold rolled steel plate (cold rolling step), and cold rolling. It includes a step of performing CAL (continuous annealing) on the steel plate (CAL step) and a step of performing temper rolling on the cold-rolled steel plate after CAL (temper rolling step). Hereinafter, each process is explained in full detail.

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

[Hot rolling process]
A hot-rolled steel sheet is manufactured by hot-rolling a slab heated at a heating temperature of 1000 ° C. or higher under normal hot-rolling conditions. More specifically, the heating temperature of a slab is 1000 degreeC-1280 degreeC, for example. When the heating temperature of the slab exceeds 1280 ° C., ear cracks are likely to occur during hot rolling. The average plastic strain ratio r _m is reduced. When the slab heating temperature is lower than 1000 ° C., it becomes difficult to ensure 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. FT is lowered average plastic strain ratio r _m exceeds 960 ° C., the FT is lower than 870 ° C., plane anisotropy Δr is increased. The hot-rolled steel sheet after finish rolling is cooled in a cooling zone and then wound on a coil. The winding temperature CT is, for example, less than 450 to 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]
A hot-rolled steel sheet is cold-rolled to produce a cold-rolled steel sheet. Cold rolling may be performed by a known method. Preferably, the optimum cold rolling rate of the cold-rolled steel sheet for drawn cans is examined in advance by changing the cold rolling rate, and the cold rolling rate is set so that the in-plane anisotropy Δr of the steel sheet is reduced. To do. When 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) process]
Continuous annealing is performed on the cold-rolled steel sheet. Since the continuous annealing line is referred to as “Continuous Annealing Line”, in this specification, the continuous annealing is referred to as “CAL”. 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 an unrecrystallized structure remains. In this case, desired mechanical characteristics cannot be obtained. On the other hand, if annealing temperature ST exceeds 800 degreeC, a recrystallized grain will coarsen and a crystal grain size number will exceed 11.0. Therefore, annealing temperature ST is 740-800 degreeC. A preferred lower limit of the annealing temperature ST is 760 ° C. The upper limit with preferable annealing temperature ST is 780 degreeC. 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 carried out without carrying out an overaging process by BOX annealing after CAL (box annealing is “Box Annealing Furnace”, overaging process is “Over Aging”, hereinafter referred to as BAF-OA). In the form of the high strength cold-rolled steel sheet, the yield point elongation YP-EL after the accelerated aging treatment is 0%, and no stretcher strain is generated. Therefore, in this embodiment, BAF-OA is not performed after CAL. Therefore, productivity is increased.

[Temper 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%, the 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 becomes less than 30%, and the press formability (drawing workability) decreases. When the rolling reduction is 0.5 to 5.0%, stretcher strain is not generated, and excellent press formability (drawing workability) is also obtained.

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

[Plating treatment]
You may implement a plating process with respect to the above-mentioned cold-rolled steel sheet for drawn cans. The plating process is, for example, any one of Ni plating process, Ni diffusion plating process, Sn plating process, and tin-free steel (TFS) plating process. For example, the Ni plating process, the Sn plating process, and the TFS plating process are performed on the cold-rolled steel sheet after the temper rolling process.

When performing 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 (as Ni adhesion amount, 4.45 to 44.5 g / m ² ). It is.

  When the Ni diffusion plating process is performed, the Ni plating process is performed after the cold rolling process and before the CAL process. 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 having various chemical compositions were produced under various production conditions, and mechanical properties and r values were investigated.

[Method for producing test material]
Slabs of steels A to Q having chemical compositions shown in Table 1 were produced.

  The slab of each test number was hot rolled under the hot rolling conditions shown in Table 2 (slab heating temperature (° C.), finish rolling temperature FT (° C.), winding temperature CT (° C.)), and hot rolled steel sheet Manufactured.

  After pickling the hot rolled steel sheet, cold rolling was performed under the cold rolling conditions (cold rolling ratio) shown in Table 2 to produce a cold rolled steel sheet having a thickness of 0.25 mm. For the cold rolled steel sheet of test number 4, Ni diffusion plating treatment was performed. Specifically, a Ni plating film was formed on the front and back surfaces of the cold-rolled steel sheet by electroplating before CAL. The film thicknesses of the Ni plating films on the front surface and the back surface were both 2 μm. For cold-rolled steel sheets with test numbers other than test number 4, no plating treatment was performed.

  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 an annealing temperature ST (° C.) for 25 seconds. Thereafter, gas cooling with nitrogen gas was performed. In gas cooling, the average cooling rate from the annealing temperature ST (° C.) to 50 ° C. or less was 25 ° C./second.

  In 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 cold-rolled steel sheets having 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 reduction in temper rolling was 1.8% in all cases. The cold rolled steel sheet used as a test material was manufactured by the above manufacturing process.

[Test method]
[Microstructure observation and grain size number measurement]
In the L cross section of the cold-rolled steel sheet after the temper rolling, an optical microscope observation was performed to identify the structure of the cold-rolled steel sheet. The identified results are shown in Table 2. All of the microstructures were ferrite single phase structures. Furthermore, the crystal grain size number of the ferrite grain of the cold rolled steel sheet of each test number was determined by the above-described method in accordance with JIS G 0552 (2013). The obtained results are shown in Table 2.

[Mechanical property evaluation test]
JIS No. 5 tensile test pieces were prepared from the cold-rolled steel sheets having the respective test numbers. 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 produced tensile test piece. Specifically, an aging treatment for 1 hour at 100 ° C. was performed on each tensile test piece.

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

[R _m value and Δr value measurement test]
Against cold-rolled steel sheet of each test number, JIS Z 2254 (2008) the plastic strain ratio test performed in conformity to the average plastic strain amount when 15% plastic strain ratio r _m and the in-plane anisotropy Δr Asked. Table 2 shows the obtained results.

[Test results]
Referring 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 with these test numbers, the crystal 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 is 1.35 greater than the in-plane anisotropy Δr is the -0.30～ + 0.15, were more press formability and surface roughening resistance.

  Furthermore, 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, the yield point elongation. 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. Furthermore, in the annealing process, CAL and BAF-OA were performed, and the annealing temperature ST was also low at less than 740 ° C. As a result, the average plastic strain ratio r _m is as low as 1.35 or less, press formability is low.

  In test number 8, the C content was too low. As a result, the crystal grain size number was less than 11.0, and the rough skin resistance was low. Furthermore, the yield point strength was also low, less than 220 MPa. Furthermore, 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 was generated.

  In test number 10, F1 exceeded the upper limit of formula (1). Therefore, the crystal grain size number was less than 11.0, and the rough skin resistance was low. Furthermore, 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 was generated. Furthermore, the yield point strength YP exceeded 390 MPa, and the total elongation EL was less than 32%. Since F1 is less than the lower limit of the formula (1) and the amount of dissolved C is excessively large, stretcher strain is generated and the strength is excessively increased. As a result, the total elongation EL is considered to be low.

  In test number 12, the C content was too high. Therefore, the crystal grain size number was less than 11.0, and the rough skin resistance was low. Furthermore, 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 is as low as 1.35 or less, press formability is low. Moreover, the crystal 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 crystal grain size number was less than 11.0, and the rough skin resistance was low. Furthermore, 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 crystal grain size number was less than 11.0, and the rough skin resistance was low. Furthermore, 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 was generated.

In test number 18, the annealing temperature ST was too low. Therefore, the average plastic strain ratio r _m is as low as 1.35 or less, further, in-plane anisotropy Δr is lower than -0.30, the press formability is low. Furthermore, 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 crystal grain size number was less than 11.0, and the rough skin resistance was low.

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

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

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

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

  The embodiment of the present invention has been described above. However, the above-described embodiment is merely an example for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately changing the above-described embodiment without departing from the spirit thereof.

Claims (6)

A cold rolled steel sheet for a drawing can,
% By 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: containing 0 to 0.0030%, the balance being a chemical composition consisting of Fe and impurities,
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 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, 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 a drawing can according to claim 1, further comprising:
A cold-rolled steel sheet for a drawing can provided on the surface 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. The slab having the chemical composition according to claim 1 is heated to 1000 ° C. or higher, finish-rolled at 870 to 960 ° C., cooled after finish rolling and wound at less than 450 to 700 ° C. Manufacturing process;
Cold rolling the hot-rolled steel sheet to produce a cold-rolled steel sheet having a thickness of 0.15 to 0.50 mm;
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 Claim 3, Comprising:
In the step of manufacturing the hot-rolled steel sheet, the slab is heated at 1100 to 1230 ° C, wound up at 600 to 670 ° C, and the hot-rolled steel sheet is manufactured. It is a manufacturing method of the cold-rolled steel sheet for drawn cans according to claim 3 or 4, further,
After performing the tempering 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 steel sheet. It is a manufacturing method of the cold-rolled steel sheet for drawn cans according to claim 3 or 4, further,
A cold-rolled steel sheet for a drawn can, which is subjected to Ni plating on at least one surface of the cold-rolled steel sheet after the step of manufacturing the cold-rolled steel sheet and before the step of performing the continuous annealing. Production method.

Images