WO2016060248A1

WO2016060248A1 - Steel sheet for drawn can, and method for manufacturing same

Info

Publication number: WO2016060248A1
Application number: PCT/JP2015/079313
Authority: WO
Inventors: 山田　輝昭; 濃野　通博
Original assignee: 新日鐵住金株式会社
Priority date: 2014-10-17
Filing date: 2015-10-16
Publication date: 2016-04-21
Also published as: CN106795609A; CN106795609B; JP5930144B1; TWI560280B; TW201623653A; JPWO2016060248A1

Abstract

　This steel sheet for a drawn can includes C, sol. Al, and B as chemical components, and includes particulate cementite and ferrite having an average particle diameter of 2.7-4.0 µm as the microstructure thereof. This steel has a yield strength of 360-430 MPa, a total elongation of 25-32%, an elongation at yield point of 0%, and a yield ratio of 80-87% when tensile-tested after the steel sheet is subjected to an aging treatment for one hour at 100°C.

Description

Steel plate for squeezed can and method for manufacturing the same

The present invention relates to a steel plate for drawn cans and a method for producing the same, and more particularly to a high-strength cold-rolled steel plate for drawn cans and a method for producing the same.
This application claims priority based on Japanese Patent Application No. 2014-213239 filed in Japan on October 17, 2014, the contents of which are incorporated herein by reference.

Battery cans such as single 1 to single 5 batteries (batteries of international standard size 20 to 1), button batteries, large hybrid batteries, and various containers are cold-rolled steel sheets and plated steel sheets that have been plated as required , Called cold-rolled steel sheet).

This drawing process requires high dimensional accuracy, suppression of press die wear, and high productivity. Therefore, as a cold-rolled steel sheet used for drawing, a soft cold-rolled steel sheet having excellent press formability such as drawability and deep drawability has been used.

On the other hand, in recent years, cold-rolled steel sheets used for drawing have been required to have further improved strength in order to realize a thinner drawn can. For example, in recent years, with the development of electronic devices, it has been required to further increase the capacity of batteries. However, the dimensions of the external shape of the battery are already determined according to the standard. Therefore, in order to increase the filling amount of the active material of the battery, it is necessary to increase the internal volume of the battery (the internal volume of the throttle can). In order to increase the inner volume of the drawn can, it is necessary to reduce the thickness (gauge down) of the cold-rolled steel sheet for the drawn can. However, when the cold-rolled steel sheet is gauged down, the strength of the drawn can may be insufficient. In particular, the can bottom of the drawn can cannot be expected to be hardened because the amount of processing strain during drawing is small. Therefore, it is necessary to increase the strength of the cold-rolled steel sheet in order to increase the strength of the drawn can, particularly the internal / external pressure resistance at the bottom of the can.

As described above, cold-rolled steel sheets for drawn cans are required to have excellent press formability and high strength. However, it can be said that increasing the press formability and increasing the strength are technical problems that are mutually contradictory. Even if the cold-rolled steel sheet can be thinned by increasing the strength of the cold-rolled steel sheet, this cold-rolled steel sheet is expected to have a decrease in total elongation EL, that is, a decrease in press formability. For example, even if the strength of the cold-rolled steel sheet is increased, when multi-stage processing is performed as drawing, the amount of processing strain becomes large at the upper part of the can of the drawn can. There is sex. Thus, regarding cold-rolled steel sheets for drawn cans, it is not easy to achieve both high strength and excellent press formability.

In addition to the above, in cold-rolled steel sheets for drawn cans, the occurrence of stretcher strain (striped surface defects) must be suppressed during drawing. If stretcher strain occurs, a thick part (part where stretcher strain is not generated) and a thin part (part where stretcher strain is generated) are formed on the peripheral surface and bottom of the can. . That is, irregularities are formed on the peripheral surface and the bottom of the can. If the battery can (squeezed can) has such an uneven shape, the contact electrical resistance between the battery can and the battery active material is increased, which is not preferable. Further, if the squeezed can has such a concavo-convex shape, the tension rigidity of the squeezed can may be reduced, and the internal and external pressure strength of the squeezed can may be reduced. Therefore, in the cold-rolled steel sheet for drawn cans, in addition to having high strength and excellent press formability, it is also required that stretcher strain does not occur after drawing. In the following description, the fact that no stretcher strain occurs after drawing is referred to as “excellent non-St-St property”.

It should be noted that stretcher strain occurs due to the yield point elongation when the steel sheet is deformed (steady deformation that proceeds with a deformation resistance smaller than the yield point immediately after yielding). This stretcher strain can be suppressed by performing temper rolling (skin pass rolling) in which the steel sheet is rolled at a light reduction rate. However, even if the steel sheet is subjected to temper rolling, the effect of suppressing the stretcher strain is reduced with the passage of time in a steel sheet that undergoes strain age hardening.

Conventionally, niobium (Nb) -added ultra-low carbon steel and boron (B) -added low-carbon steel have been used as cold-rolled steel sheets for drawing cans in order to suppress stretcher strain. For example, IF (Interstitial Free) steel typified by Nb-added ultra-low carbon steel (Nb-SULC) or the like is less likely to age harden, so that the occurrence of stretcher strain can be prevented. However, in the Nb-added ultra-low carbon steel, the steel components are limited, so it is difficult to increase the strength of the steel. On the other hand, in the B-added low carbon steel, B is combined with nitrogen (N) in the steel, so that age hardening due to N is suppressed. However, in this B-added low carbon steel, it is necessary to suppress age hardening due to solute carbon (C) in the steel. Therefore, in the B-added low carbon steel, after the steel sheet is continuously annealed, an overaging treatment by box annealing is performed to reduce the solid solution C in the steel, thereby preventing the occurrence of stretcher strain. For example, in the overaging treatment by box annealing described above, it is necessary to anneal the steel plate at a low temperature of about 400 ° C. and then gradually cool the steel plate. In the following description, annealing by a continuous annealing line is referred to as “CAL (Continuous Annealing Line)”. Further, the overaging treatment by box annealing is referred to as “BAF-OA (Box Annealing Furnace-Over Aging)”.

This BAF-OA requires a processing time of about one week in order to perform the above-mentioned soaking and slow cooling. Therefore, when BAF-OA is performed, the productivity of cold-rolled steel sheets for drawn cans is significantly reduced. Therefore, if a cold-rolled steel sheet for a drawing can having high strength, excellent press formability, and excellent non-St-St properties can be produced without performing BAF-OA, it is very useful in the industry.

For example, Patent Document 1 discloses a steel plate for a drawing can. The steel plate for drawn cans disclosed in Patent Document 1 is a low-carbon aluminum killed steel containing B, and the C content is 0.045 to 0.100%. This Patent Document 1 describes that the upper limit of the C content is limited to 0.100% in order to prevent the steel sheet from becoming hard and reducing the drawing workability.

Japanese Patent No. 4374126

Patent Document 1 discloses a steel plate for a drawing can, but the steel plate for a drawing can disclosed in Patent Document 1 is a soft cold-rolled steel plate. Therefore, when this steel plate is gauged down, the internal and external pressure strength of the drawn can may decrease. Further, in the steel plate for a drawn can disclosed in Patent Document 1, it is difficult to suppress stretcher strain when BAF-OA is omitted. As described above, Patent Document 1 increases the strength of a cold-rolled steel sheet in order to achieve gauge down, and simultaneously improves press formability and non-St-St properties in addition to this increase in strength. Is not disclosed or suggested. That is, in the prior art, it is possible to suppress stretcher strain after aging treatment in a steel sheet for a drawn can without securing box strength by having a high C content of more than 0.15%, and without box annealing. There wasn't. In addition, the tin content specified in JIS G3303 has a C content of 0.13% or less.

The present invention has been made in view of the above circumstances, and provides a cold-rolled steel sheet for a drawing can that has high strength, excellent press formability, and excellent non-St-St properties without performing BAF-OA. The task is to do.

The gist of the present invention is as follows.
(1) A steel plate for a drawing can according to one embodiment of the present invention has, as a chemical component, C: more than 0.150 to 0.260%, Sol. Al: 0.005 to 0.100%, B: 0.0005 to 0.02%, Si: 0.50% or less, Mn: 0.70% or less, P: 0.070% or less, S: 0.00. Containing 0.5% or less, N: 0.0080% or less, Nb: 0.003% or less, Ti: 0.003% or less, with the balance being Fe and impurities, the boron content and nitrogen in the chemical components The content of the steel sheet satisfies 0.4 ≦ B / N ≦ 2.5 in terms of mass%, and the steel sheet has a microstructure with an average particle size of 2.7 to 4.0 μm, and granular cementite. The steel sheet has a thickness of 0.15 to 0.50 mm, and is obtained from a tensile test in which the tensile direction performed after the steel sheet is subjected to aging treatment at 100 ° C. for 1 hour is parallel to the rolling direction. Yield strength is YP in MPa, total elongation is EL in%, yield point YP-EL in unit% and yield ratio YR in unit%, the YP is 360 to 430 MPa, the EL is 25 to 32%, and the YP-EL is 0%. The YR is 80 to 87%.
(2) In the steel plate for a drawing can described in (1), the EL may be 27 to 32% when the plate thickness is more than 0.20 to 0.50 mm.
(3) In the steel plate for drawing cans according to (1) or (2) above, at least one of a Ni plating layer, a Ni diffusion plating layer, a Sn plating layer, and a TFS plating layer is formed on the surface of the steel plate. It may be arranged.
(4) In the method for producing a steel plate for a drawn can according to the above (1) or (2), a steelmaking step for obtaining a slab having the chemical component, and heating the slab to 1000 ° C. or more, Finish rolling at 950 ° C., cooling after finish rolling, winding at 500 to 720 ° C. to obtain a hot-rolled steel sheet, and primary cold with a cumulative rolling reduction of over 80% with respect to the hot-rolled steel sheet A primary cold-rolling step of rolling to obtain a primary cold-rolled steel sheet, and the primary cold-rolled steel sheet are heated at an average temperature increase rate of 10 to 40 ° C./second, and averaged within a temperature range of 650 to 715 ° C. Heating and then performing continuous annealing to cool between 500 to 400 ° C. at an average cooling rate of 5 to 80 ° C./second to obtain an annealed steel sheet, and no overaging treatment is performed after the annealing step The annealed steel sheet is temper-rolled at a cumulative reduction of 0.5 to 5.0%, and temper-rolled steel And a temper rolling to obtain a.
(5) In the manufacturing method of the steel plate for drawn cans described in (4) above, after the temper rolling step, the temper rolled steel plate is subjected to Ni plating treatment, Ni diffusion plating treatment, Sn plating treatment, and TFS. You may further provide the plating process which implements at least 1 of a plating process.

According to the above aspect of the present invention, it is possible to provide a steel plate for a drawing can having high strength, excellent press formability, and excellent non-St-St properties without performing BAF-OA. This steel sheet is excellent in press formability, can suppress the occurrence of stretcher strain, and can be gauged down.

It is a tensile test result after accelerated aging treatment of a conventional steel plate for drawn cans, and is a stress-strain curve showing an enlarged vicinity of the yield point. FIG. 5 is a tensile test result after accelerated aging treatment of a cold-rolled steel sheet for drawn cans according to an embodiment of the present invention, and is a stress-strain curve showing an enlarged vicinity of the yield point. It is an optical microscope photograph which shows the microstructure of the conventional cold-rolled steel plate for drawn cans. It is an optical microscope photograph which shows the microstructure of the cold-rolled steel plate for drawn cans which concerns on this embodiment. It is a graph which shows the relationship between C content (%) of a cold-rolled steel plate, and yield point elongation YP-EL (%). It is a graph which shows the relationship between C content (%) and total elongation EL (%) of a cold-rolled steel plate.

Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the configuration disclosed in the present embodiment, and various modifications can be made without departing from the spirit of the present invention. Moreover, a lower limit value and an upper limit value are included in the numerical limit range described below. Numerical values indicating “over” or “less than” are not included in the numerical range. “%” Regarding the content of each element means “mass%”.

The present inventors investigated and examined the characteristics of steel plates for drawn cans (hereinafter referred to as cold rolled steel plates), and obtained the following findings (i) to (iv). First, findings (i) and (ii) will be described.

(I) In the cold-rolled steel sheet according to the present embodiment, if the C content exceeds 0.150, the steel is solid-solution strengthened by the solid solution C in the steel, and the yield strength YP of the cold-rolled steel sheet increases. The yield strength YP in the rolling direction (L direction) after natural aging is 360 MPa or higher, which is higher than the yield strength of the conventional cold rolled steel sheet for drawn cans. Therefore, if this cold-rolled steel sheet is used, a drawn can excellent in internal and external pressure strength can be obtained even if the gauge is down.

(Ii) In the cold-rolled steel sheet according to this embodiment, even if the C content is increased to more than 0.150, the average temperature increase rate of CAL (continuous annealing) is set to 10 to 40 ° C./second, and the annealing temperature (soaking) If the temperature is higher than the recrystallization completion temperature and the ferrite single-phase region temperature (for example, 650 to 715 ° C.) and the subsequent average cooling rate between 500 to 400 ° C. is 5 to 80 ° C./second, Even if solid solution C is present in the steel, a cold-rolled steel sheet having excellent non-St-St properties can be obtained.

Fig. 1 shows a stress-strain diagram near the yield point of a conventional cold-rolled steel sheet for drawn cans. FIG. 2 shows a stress-strain diagram in the vicinity of the yield point (0.2% proof stress) of the cold-rolled steel sheet for drawn cans according to this embodiment. The C content of the cold rolled steel sheet subjected to the tensile test of FIG. 1 is 0.056% by mass, and the C content of the cold rolled steel sheet subjected to the tensile test of FIG. 2 is 0.153% by mass. is there. The cold-rolled steel sheet shown in FIGS. 1 and 2 was manufactured under conditions that satisfy the method for manufacturing a cold-rolled steel sheet according to this embodiment, which will be described later. Specifically, after performing CAL under the above conditions, the cold-rolled steel sheets of FIGS. 1 and 2 were manufactured without performing BAF-OA. From the manufactured cold-rolled steel sheet, a JIS No. 5 tensile test piece having a parallel part parallel to the L direction (rolling direction) was produced. An accelerated aging treatment was performed on the produced tensile test piece. Specifically, as an accelerated aging treatment, an aging treatment for 1 hour at 100 ° C. was performed on each tensile test piece. This accelerated aging treatment corresponds to an aging at which natural aging is almost saturated. Using the tensile test piece after the accelerated aging treatment, a tensile test was carried out at room temperature (25 ° C.) and in the atmosphere, and the stress-strain diagrams of FIGS. 1 and 2 were obtained.

In the conventional cold-rolled steel sheet having a low C content (FIG. 1), the yield point drop occurred and the yield point elongation YP-EL occurred. This is because even if stress is applied from the outside, the dislocation does not move (fixed) 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 and moves at the yield point all at once. caused by. In the conventional cold-rolled steel sheet (FIG. 1), the yield point elongation YP-EL occurs because the dislocation fixation and release due to the Cottrell effect are repeated even after yielding.

In contrast, in the cold-rolled steel sheet according to the present embodiment having a high C content (FIG. 2), no yield point drop was confirmed, and no yield point elongation YP-EL occurred. When the stress-strain diagram in FIG. 2 is observed, unlike the stress-strain diagram in FIG. 1, the plot interval is remarkably shortened before the yield point is reached (the stress change and strain change per unit time are Small). That is, in the cold-rolled steel sheet according to the present embodiment (FIG. 2), when a stress is applied from the outside, plastic deformation starts locally even before the yield point, and the yield point elongation YP− as shown in FIG. A unique phenomenon occurred in which EL was not observed.

Therefore, the microstructure in the L cross section (cross section parallel to the rolling direction) of the cold-rolled steel sheet of FIGS. 1 and 2 was observed with an optical microscope. 3 is a microstructure image of the L cross section of the cold rolled steel sheet subjected to the tensile test of FIG. 1, and FIG. 4 is a microstructure image of the L cross section of the cold rolled steel sheet subjected to the tensile test of FIG. is there.

3 and 4, the white structure is ferrite 10 and the black structure is granular cementite 20. As observed from FIGS. 3 and 4, the microstructure of the cold-rolled steel sheet of FIGS. 3 and 4 was a structure mainly containing ferrite and granular cementite. However, the average ferrite grain size of the cold rolled steel sheet of FIG. 4 having a high C content was 4.0 μm or less, which is smaller than the average ferrite grain diameter of the cold rolled steel sheet of FIG. Further, the ferrite structure of the cold-rolled steel sheet of FIG. 4 appears to be a mixed grain containing coarse grains and fine grains as compared with the cold-rolled steel sheet of FIG.

Considering the results of the above tensile test and structure observation, a unique phenomenon in the vicinity of the yield point indicated by the cold-rolled steel sheet (cold-rolled steel sheet having a high C content) according to this embodiment is inferred as follows. . In the cold-rolled steel sheet according to the present embodiment (cold-rolled steel sheet having a high C content), the average grain size of the ferrite grains becomes smaller and the ferrite grains are likely to be mixed grains compared to a cold-rolled steel sheet having a low C content. . That is, when a cold-rolled steel sheet having a microstructure unique to this embodiment is deformed, among the ferrite grains that are mixed grains, the deformation starts before the yield point before the coarse ferrite grains, and the coarse ferrite grains After that, the deformation of fine ferrite grains starts. Thus, in the cold-rolled steel sheet according to the present embodiment, when stress is applied from the outside, deformation starts sequentially from the ferrite having a large grain size, so even if solute C exists in the steel, the yield point It is considered that the elongation YP-EL does not appear in the stress-strain diagram. As a result, it is considered that the generation of stretcher strain is suppressed.

Based on the above findings, the present inventors further investigated the relationship between C content and yield point elongation YP-EL. FIG. 5 shows the relationship between the C content (mass%) of the cold rolled steel sheet and the yield point elongation YP-EL (%). This FIG. 5 was obtained by investigating a cold-rolled steel sheet controlled to have a microstructure mainly containing ferrite and granular cementite.

As shown in FIG. 5, as the C content increases, the yield point elongation YP-EL decreases rapidly. Specifically, when the C content exceeds 0.150, the yield point elongation YP-EL becomes 0%. Further, as described above, the C content is more than 0.150, and the yield strength YP in the L direction after the accelerated aging treatment is 360 MPa or more. That is, when the C content exceeds 0.150 in addition to the control of the microstructure and the like, strength and non-St-St properties are satisfied among the properties required for cold-rolled steel sheets for drawn cans.

Specifically, the C content is more than 0.150, the CAL average heating rate is 10 to 40 ° C./second, the annealing temperature is equal to or higher than the recrystallization completion temperature, and the ferrite single-phase region temperature (for example, 650 When the average cooling rate between 500 and 400 ° C. is 5 to 80 ° C./second, a ferrite structure peculiar to this embodiment is formed as described above. Therefore, if the C content is more than 0.150 and CAL is performed under the above conditions, the microstructure mainly includes ferrite and granular cementite, and the average grain size of the ferrite grains becomes 4.0 μm or less, yield strength. YP is 360 MPa or more and the yield point elongation YP-EL is 0%.

In addition, as described above, in order to prevent the occurrence of stretcher strain, BAF-OA or the like has been performed on conventional steel plates. However, the conventional steel sheet is characterized by a low C content. In the case of a steel sheet with a high C content such that the C content exceeds 0.150, even if BAF-OA or the like is performed, it is difficult to sufficiently reduce the solid solution C in the steel. It was substantially difficult to control YP-EL to 0%. In the steel sheet according to the present embodiment, even if the C content exceeds 0.150, YP-EL can be controlled to 0% by forming the ferrite structure by controlling the manufacturing conditions.

On the other hand, if the C content is too high, the cold-rolled steel sheet is excessively hardened, and the total elongation EL (%) is lowered. As a result, the press formability is lowered. The inventors investigated the relationship between C content and total elongation EL. And knowledge (iii) was obtained.

(Iii) In the cold-rolled steel sheet according to the present embodiment, if the C content is 0.260% or less and the structure is controlled, the total elongation EL in the L direction (rolling direction) after natural aging becomes a conventional drawn can. It becomes 25% or more which is about the same or more as the total elongation of the cold-rolled steel sheet. Therefore, a cold-rolled steel sheet excellent in press formability can be obtained.

FIG. 6 shows the relationship between the C content (mass%) and the total elongation EL (%) of the cold-rolled steel sheet. This FIG. 6 was obtained by investigating a cold-rolled steel sheet controlled to have a microstructure mainly containing ferrite and granular cementite.

As shown in FIG. 6, when the C content is more than 0.150 to 0.260%, the total elongation EL becomes substantially constant as the C content increases. However, when the C content exceeds 0.260%, the total elongation EL decreases rapidly. Therefore, if the C content is 0.260% or less, excellent total elongation EL is maintained. Specifically, if the C content is 0.260% or less, the total elongation EL is 25% or more. Further, as described above, in order to satisfy the strength and the non-St-St property, the lower limit of the C content is set to more than 0.150. That is, in the cold-rolled steel sheet for drawn cans according to this embodiment, the C content is set to more than 0.150 to 0.260%.

Furthermore, the present inventors also investigated the suppression of stretcher strain caused by N in addition to the suppression of stretcher strain caused by C described above. And knowledge (iv) was obtained.

(Iv) If the C content is set to more than 0.150 to 0.260% and the B content and the N content are controlled to be 0.4 ≦ B / N ≦ 2.5, it is caused by C. Both the occurrence of stretcher strain and the occurrence of stretcher strain due to N can be suppressed.

CAL (continuous annealing) is performed on cold-rolled steel sheets of aluminum killed steel having a C content of over 0.150 to 0.260% and a B / N ratio of 0.4 to 2.5. At this time, as described above, the average rate of temperature increase is set to 10 to 40 ° C./second, the annealing temperature is set to the recrystallization completion temperature or higher and the ferrite single phase region temperature (for example, 650 to 715 ° C.), and the subsequent 500 to 400 The average cooling rate during 5 ° C. is 5-80 ° C./sec. In this case, the strength and press formability of the cold-rolled steel sheet and the non-St-St property due to C are improved, and B is combined with N to form a nitride. As a result, the generation of stretcher strain due to N is also suppressed.

Hereinafter, the cold-rolled steel sheet for drawn cans according to the present embodiment will be described in detail.

[Chemical composition]
The cold-rolled steel sheet for drawn cans according to the present embodiment has C, Sol. Al and B are included, and the balance consists of Fe and impurities.

In addition, “impurities” refer to materials mixed from ore, scrap, or production environment as raw materials when industrially manufacturing steel. Among these impurities, Si, Mn, P, S, and N are preferably limited as follows in order to sufficiently exhibit the effects of the present embodiment. Moreover, since it is preferable that there is little content of an impurity, it is not necessary to restrict | limit a lower limit and the lower limit of an impurity may be 0%.

C: Over 0.150 to 0.260%
Carbon (C) is dissolved to increase the strength of the steel. If the strength of the steel increases, the cold rolled steel sheet can be gauged down. If the C content exceeds 0.150, the yield strength YP in the L direction after the accelerated aging treatment can be set to 360 MPa or more. Furthermore, by performing CAL under the conditions described later, the average grain size of the ferrite structure becomes 4.0 μm or less, and the ferrite grains tend to be mixed grains including coarse grains and fine grains. As a result, the yield point elongation YP-EL after the accelerated aging treatment can be reduced to 0%. If the C content is 0.15 or less, the above effect cannot be obtained. On the other hand, if the C content exceeds 0.260%, the hardness of the cold-rolled steel sheet becomes too high, and the total elongation EL after natural aging is saturated (after accelerated aging treatment) decreases as shown in FIG. . In this case, the press formability of the cold rolled steel sheet is lowered. Therefore, the C content is more than 0.150 to 0.260%. C is an austenite forming element. In the cold rolled steel sheet according to this embodiment, in order to control the microstructure, the lower limit of the C content is preferably 0.153%, 0.155%, or 0.160%. The upper limit with preferable C content is less than 0.260%, More preferably, it is 0.250%. Ferrite grains tend to be mixed.

Si: 0.50% or less Silicon (Si) is an unavoidable impurity. 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 limited to 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. However, since it is difficult to make the Si content 0% stably industrially, the lower limit of the Si content may be 0.0001%.

Mn: 0.70% or less Manganese (Mn) is an unavoidable impurity. 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. Further, Mn is an austenite forming element and is not added to the steel in order to control the microstructure in the cold rolled steel sheet according to the present embodiment. When the Mn content is more than 0.70%, it is difficult to obtain the mechanical characteristics peculiar to the steel sheet according to the present embodiment. Therefore, the Mn content is limited to 0.70% or less. The upper limit with preferable Mn content is less than 0.70%. The Mn content is preferably as low as possible. However, since it is difficult to make the Mn content 0% stably industrially, the lower limit of the Mn content may be 0.0001%.

P: 0.070% or less Phosphorus (P) is an unavoidable impurity. P generally 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 brittleness resistance after forming into a drawn can decreases. For deep drawn cans, for example, brittle fracture may occur due to impact at the time of dropping at a low temperature such as −10 ° C., and end portions of the can side wall may brittle fracture due to bending strain. Such a break is referred to as a secondary work brittle crack. When the P content is excessive, secondary work brittle cracks are likely to occur. Therefore, the P content is limited to 0.070% or less. However, since it is difficult to make the P content 0% stably industrially, the lower limit of the P content may be 0.0001%.

S: 0.05% or less Sulfur (S) is an unavoidable impurity. S causes brittle cracks in the surface layer of the steel sheet during hot rolling, and causes rough edges in the hot-rolled steel strip. Therefore, the S content is limited to 0.05% or less. The S content is preferably as low as possible. However, since it is difficult to make the S content 0% stably industrially, the lower limit of the S content may be 0.0001%.

Sol. Al: 0.005 to 0.100%
Aluminum (Al) deoxidizes steel. Al further enhances the surface quality of the slab during continuous casting. If the Al content is too low, these effects cannot be obtained. On the other hand, if the Al content is too high, the above effect is saturated and the production cost is increased. Therefore, the Al content is 0.005 to 0.100%. The Al content in the cold-rolled steel sheet for drawn cans according to this embodiment is Sol. It means the content of Al (acid-soluble aluminum).

N: 0.0080% or less Nitrogen (N) is an unavoidable impurity. N is an element that age hardens the steel, and therefore reduces the press formability of the cold-rolled steel sheet and generates stretcher strain. In the cold-rolled steel sheet according to the present embodiment, the below-described B is contained in the steel, and N is combined with B to form a nitride, thereby suppressing age hardening due to solute N. However, if the N content is too high, age hardening due to solute N tends to occur. Therefore, the N content is limited to 0.0080% or less. The N content is preferably as low as possible. However, since it is difficult to make the N content 0% stably industrially, the lower limit of the N content may be 0.0005%.

B: 0.0005 to 0.02%
Boron (B) combines with N to form BN (boron nitride), and reduces solid solution N. Thereby, age hardening by the solid solution N is suppressed. B further randomizes the texture of the cold-rolled steel sheet to bring the r value (Rankford value), which is the plastic strain ratio, closer to 1. This improves the earring characteristics (the degree of unevenness of the can height in the circumferential direction of the can that occurs after the drawing of the drawn can). B is a ferrite-forming element, and is added to control the microstructure in the cold-rolled steel sheet according to the present embodiment. If the B content is less than 0.0005%, these effects cannot be obtained. On the other hand, if the B content exceeds 0.02%, the above effect is saturated. Therefore, the B content is 0.0005 to 0.02%. The lower limit of the B content is preferably 0.0010% or 0.0015%.

Furthermore, in the cold-rolled steel sheet according to this embodiment, the contents of B and N are specified in relation to each other. As described above, when the solute N is excessive in the steel, the steel is age hardened. Therefore, B is contained in steel to form BN. On the other hand, if the solid solution B is excessive in the steel, the cold-rolled steel sheet is hardened or the earring properties are lowered. Therefore, it is necessary to define the contents of B and N in relation to each other. Specifically, the B content and the N content in the chemical component must satisfy 0.4 ≦ B / N ≦ 2.5 in mass%. When the contents of B and N satisfy the above conditions, it is possible to preferably suppress the occurrence of stretcher strain due to the solid solution N while simultaneously suppressing the deterioration of the characteristics due to the solid solution B. The lower limit of the value of B / N is preferably 0.8.

In the cold-rolled steel sheet according to the present embodiment, in addition to the impurities described above, niobium (Nb), titanium (Ti), copper (Cu), nickel (Ni), chromium (Cr), and tin (Sn) are also limited. It is preferable. Specifically, in order to sufficiently exhibit the effects of the present embodiment, Nb: 0.003% or less, Ti: 0.003% or less, Cu: 0.5% or less, Ni: 0.5% or less, It is preferable to limit to Cr: 0.3% or less and Sn: 0.05% or less. In particular, Ti forms TiN and affects the formation of the microstructure, so it is preferable to limit as described above. The content of these impurities is preferably as low as possible. However, since it is difficult to make the content of these impurities 0% stably industrially, the lower limit of the content of these impurities may be 0.0001%.

The above chemical components may be measured by a general analysis method for steel. For example, the chemical components described above may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Specifically, it can be specified by collecting a granular test piece from the center position of the steel plate and performing chemical analysis under conditions based on a calibration curve prepared in advance. C and S may be measured using a combustion-infrared absorption method, and N may be measured using an inert gas melting-thermal conductivity method.

[Microstructure]
The cold-rolled steel sheet according to the present embodiment mainly includes ferrite having an average particle diameter (average diameter) of 2.7 to 4.0 μm and granular cementite as a microstructure. Moreover, since BN mentioned above is a fine precipitate and cannot be observed in the case of a low magnification, this BN may be included as a microstructure. In the cold-rolled steel sheet according to the present embodiment, in addition to controlling the above-described chemical components, by controlling to the above-described microstructure, high strength, excellent press formability, and non-St-St properties are also excellent. A cold-rolled steel sheet can be obtained.

The above-mentioned ferrite, granular cementite and BN are preferably 95 to 100 area% in total in the microstructure. That is, pearlite, martensite, retained austenite, etc., which are structures other than ferrite, granular cementite, and BN, are preferably limited to less than 5 area% in total. Or it is preferable not to include. The total area fraction of the structure other than ferrite, granular cementite, and BN is preferably as low as possible. Therefore, it is more preferable that the cold-rolled steel sheet according to the present embodiment includes only ferrite, granular cementite, and BN as a microstructure.

Moreover, as described above, in the cold-rolled steel sheet according to this embodiment, the ferrite grains tend to be mixed grains including coarse grains and fine grains. Although it is difficult to quantitatively define this mixed grain, it is considered that this microstructure has an influence on the mechanical characteristics peculiar to the steel sheet according to the present embodiment.

In the cold-rolled steel sheet according to this embodiment, each constituent phase included in the microstructure is defined as follows. Ferrite and ferrite grains are defined as a region having a body-centered cubic structure (bcc) due to diffusion transformation and having a crystal orientation angle difference of 0 to less than 15 °. Martensite and martensite grains have a body-centered cubic structure (bcc) or body-centered tetragonal structure (bct) resulting from a non-diffusion transformation, and are defined as regions where the crystal orientation angle difference is 0 or more and less than 15 °. Cementite is defined as a compound of Fe and C having an orthorhombic structure (Fe ₃ C). The pearlite and the pearlite block have a layered structure composed of ferrite and cementite, and are defined as a region in which the crystal orientation angle difference of ferrite in the pearlite is 0 or more and less than 9 °. Granular cementite is defined as cementite not contained in the pearlite block. BN is defined as a compound of B and N having a hexagonal structure or a cubic structure.

The above microstructure may be obtained by observing the L cross section (cross section parallel to the rolling direction) of the cold-rolled steel sheet with an optical microscope. Moreover, what is necessary is just to obtain | require the average particle diameter of a ferrite based on the cutting method of JIS G0551 (2013). The area fraction of each constituent phase may be obtained by image analysis of a microstructural photograph.

[Mechanical properties]
The cold-rolled steel sheet according to this embodiment has a thickness of 0.15 to 0.50 mm, and is obtained from a tensile test performed after the cold-rolled steel sheet is subjected to an aging treatment (accelerated aging treatment) at 100 ° C. for 1 hour. Yield strength is MP in MPa, total elongation is EL in unit%, yield point elongation is YP-EL in unit%, and yield ratio is YR in unit%.
YP is 360 to 430 MPa,
EL is 25-32%,
YP-EL is 0%,
YR is 80 to 87%.
Here, a tensile test is implemented according to JISZ2241 (2011) in room temperature (25 degreeC) air | atmosphere using the tensile test piece whose parallel part is parallel to the L direction (rolling direction).

YP: 360 to 430 MPa
When the yield strength YP is 360 MPa or more, even if the cold-rolled steel sheet is thinned (gauge down), a drawn can having excellent internal and external pressure strength can be obtained. On the other hand, the upper limit of the yield strength YP is not particularly limited. However, if the yield strength YP is too high, press molding becomes difficult, so the yield strength YP may be 430 MPa or less. In addition, since the cold rolled steel sheet according to the present embodiment is technically characterized in that it does not show a clear yield point as described above, the yield strength YP means 0.2% proof stress.

EL: 25-32%
If the total elongation EL is 25% or more, press formability (drawing workability) as a cold-rolled steel sheet for drawn cans can be satisfied. On the other hand, the upper limit of the total elongation EL is not particularly limited because a larger value is preferable. However, since it is difficult to make the total elongation EL more than 32% industrially stable, the upper limit of the total elongation EL may be 32%, and more preferably 30%. The total elongation EL means the sum of elastic elongation and permanent elongation.

As described above, it is preferable that the cold-rolled steel sheet is thinned. Therefore, the thickness of the cold-rolled steel sheet according to this embodiment is 0.15 to 0.50 mm. However, the value of the total elongation EL increases as the plate thickness increases within this plate thickness range. Accordingly, when priority is given to improving press formability (drawing workability), the plate thickness may be more than 0.20 to 0.50 mm and the total elongation EL may be 27 to 32%.

YP-EL: 0%
If the yield point elongation YP-EL is 0%, steady deformation that proceeds with a deformation resistance smaller than the yield point immediately after yielding can be suppressed, so that the occurrence of stretcher strain can be suppressed. In the cold-rolled steel sheet according to the present embodiment, the yield point elongation YP-EL is 0%. The deformation (stress) is smaller than the yield point (0.2% proof stress) immediately after yielding (deformation (stress)). This means that (strain) does not progress. That is, in the cold-rolled steel sheet according to the present embodiment, the yield point elongation YP-EL is 0% when stress-strain is observed immediately after yielding (after reaching 0.2% proof stress) without lowering the yield point. It means that the curve indicates work hardening.

YR: 80-87%
If the yield ratio YR is 80% or more, it means that the yield strength YP is sufficiently higher than the tensile strength TS. Therefore, the cold-rolled steel sheet can be thinned (gauge down), and a drawn can excellent in internal and external pressure strength can be obtained. That is, when comparing the bottom of the can with a small amount of processing strain during drawing and the top of the barrel with a large amount of processing strain during drawing, the difference in strength between the bottom of the can and the top of the can is reduced in the drawn can after molding. It becomes possible to obtain a drawn can having uniform mechanical quality. On the other hand, the upper limit of the yield ratio YR is not particularly limited. However, if the yield ratio YR is too high, press forming becomes difficult, so the yield ratio YR may be 87% or less. The yield ratio YR means the percentage of the value obtained by dividing the yield strength YP in unit MPa by the tensile strength TS in unit MPa.

[Plating layer]
The cold-rolled steel sheet according to this embodiment includes a Ni plating layer, a Ni diffusion plating layer, a Sn plating layer, and a tin-free steel (TFS) plating layer (with a metal Cr layer) on the surface (on the plate surface) of the cold-rolled steel sheet. At least one of two plating layers including a Cr hydrated oxide layer may be disposed. By arranging the plating layer on the surface of the cold-rolled steel sheet, the surface appearance is improved, and the corrosion resistance, chemical resistance, stress crack resistance, and the like are improved.

Hereinafter, a method for producing a cold-rolled steel sheet for a drawn can according to the present embodiment will be described in detail.

An example of a method for manufacturing a cold rolled steel sheet for a drawn can according to the present embodiment will be described. The manufacturing method of the cold-rolled steel sheet for drawn cans according to the present embodiment includes a step of obtaining a slab (steel making step), a step of obtaining a hot-rolled steel plate (hot-rolling step), and a step of obtaining a primary cold-rolled steel plate (primary cooling). Extending step), a step of obtaining an annealed steel plate (annealing step), and a step of obtaining a temper rolled steel plate (temper rolling).

[Steel making process]
In the steelmaking process, C: more than 0.150 to 0.260%, Sol. Al: 0.005 to 0.100%, B: 0.0005 to 0.02%, Si: 0.50% or less, Mn: 0.70% or less, P: 0.070% or less, S: 0.00. Contains 0.5% or less, N: 0.0080% or less, Nb: 0.003% or less, Ti: 0.003% or less, with the balance consisting of Fe and impurities, boron content and nitrogen content in chemical components The amount of the molten steel satisfying 0.4 ≦ B / N ≦ 2.5 in mass% is manufactured. A slab is manufactured from the manufactured molten steel. For example, the slab may be cast by a casting method such as a normal continuous casting method, an ingot method, or a thin slab casting method. In the case of continuous casting, the steel may be once cooled to a low temperature (for example, room temperature) and reheated, and then the steel may be hot-rolled, or the steel immediately after casting (cast slab) You may hot-roll continuously.

[Hot rolling process]
In the hot rolling process, the slab after the steel making process is heated to 1000 ° C. or higher (eg, 1000 to 1280 ° C.), finish-rolled at 840 to 950 ° C., cooled after finish rolling, and wound at 500 to 720 ° C. A hot-rolled steel sheet.

When the coiling temperature CT exceeds 720 ° C., cementite in the hot-rolled steel sheet _(Fe 3 C) becomes coarse agglomerate. In this case, the total elongation EL of the cold rolled steel sheet can be reduced. If coiling temperature CT is less than 500 degreeC, the cementite in a hot-rolled steel plate will become a hard structure | tissue. Therefore, the total elongation EL of the cold rolled steel sheet can be reduced. Therefore, a preferable winding temperature CT is 500 to 720 ° C. In order to preferably control the microstructure, the lower limit of the coiling temperature CT is more preferably 600 ° C.

[Primary cold rolling process]
In the primary cold rolling process, the primary cold rolled steel sheet having a thickness of 0.15 to 0.50 mm is obtained by subjecting the hot rolled steel sheet after the hot rolling process to primary cold rolling with a cumulative reduction ratio exceeding 80%. Manufacturing.

In primary cold rolling, the optimum cold rolling rate of the cold-rolled steel sheet for drawn cans is examined by changing the cold rolling rate, and the in-plane anisotropy Δr of the steel sheet is substantially 0 (specifically, Δr is The cold rolling rate is set so that the range is +0.15 to -0.08. Further, the cold rolling rate is set so that the primary cold-rolled steel sheet has a microstructure (working structure) suitable for use in the subsequent process. In the primary cold rolling, the cumulative rolling reduction is set to more than 80%. The lower limit of the cumulative rolling reduction is preferably 84%. On the other hand, the upper limit of the cumulative rolling reduction is not particularly limited. However, since it is difficult to make the cumulative rolling reduction more than 90% industrially stable, the upper limit of the cumulative rolling reduction may be set to 90%. The cumulative rolling reduction is a rolling reduction calculated from the difference between the inlet plate thickness immediately before the first pass and the outlet plate thickness immediately after the final pass in primary cold rolling.

The plate thickness of the primary cold-rolled steel plate is preferably 0.151 to 0.526 mm. If the plate thickness exceeds 0.526 mm, it is difficult to obtain excellent earring properties. If the plate thickness is less than 0.151 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 thickness of the primary cold-rolled steel sheet is preferably 0.151 to 0.526 mm.

[Annealing process (CAL process)]
In the annealing step, the primary cold-rolled steel sheet after the primary cold-rolling step is heated at an average rate of temperature increase of 10 to 40 ° C./second and is not less than the recrystallization completion temperature and the ferrite single-phase region temperature (eg, 650 to 715). ° C), and then subjected to continuous annealing in which the average cooling rate between 500 and 400 ° C is 5 to 80 ° C / second to produce an annealed steel sheet.

If the temperature of the primary cold-rolled steel sheet is raised at an average heating rate HR: 10 to 40 ° C./sec in the annealing process, the microstructure is preferably controlled. In the temperature raising process of the annealing process, the work structure of the primary cold-rolled steel sheet is recovered, and recrystallization nuclei are generated in the work structure. By raising the temperature of the primary cold-rolled steel sheet under the above conditions, the recrystallization process of the processed structure is preferably controlled, so that a microstructure specific to this embodiment can be preferably obtained. In this heating process, it is more preferable that the primary cold-rolled steel sheet is heated at an average heating rate of 500 to 700 ° C. at 10 to 20 ° C./second.

The annealing temperature (soaking temperature) ST is equal to or higher than the recrystallization completion temperature and the ferrite single phase temperature. In the case of the above-described chemical components of the steel plate for a can according to the present embodiment, the temperature range of 650 to 715 ° C. is equal to or higher than the recrystallization completion temperature and corresponds to the ferrite single phase temperature. By soaking in this temperature range, the microstructure is preferably controlled. In addition, it is preferable that the upper limit of annealing temperature ST is 710 degreeC or 705 degreeC.

When the annealing temperature ST exceeds the ferrite single-phase region temperature (for example, more than 715 ° C.), annealing occurs at the two-phase region temperatures of ferrite and austenite, so that pearlite is formed during cooling after soaking. Therefore, the above microstructure cannot be obtained. In the case of a microstructure containing pearlite, the yield ratio YR decreases. Furthermore, the average particle diameter of ferrite becomes larger than 4.0 μm. When the annealing temperature ST is 650 to 715 ° C., the microstructure is preferably controlled. Further, the holding time at the annealing temperature ST may be 15 to 30 seconds.

¡After soaking at the annealing temperature ST, the steel plate is cooled. At this time, the average cooling rate CR between 500 and 400 ° C. is set to 5 to 80 ° C./second. If the average cooling rate CR exceeds 80 ° C./second, the amount of solute C becomes too high. In this case, the yield point elongation YP-EL after the accelerated aging treatment becomes larger than 0%. On the other hand, if the average cooling rate CR is less than 5 ° C./second, the amount of solid solution C becomes too low. In this case, the yield strength YP is less than 360 MPa. If the average cooling rate CR between 500 and 400 ° C. is 5 to 80 ° C./second, a solid solution C amount of about 5 to 50 ppm is secured. Therefore, the yield strength YP after the accelerated aging treatment is 360 MPa or more, and the yield point elongation YP-EL is 0%. Furthermore, an excellent total elongation EL and a high yield ratio YR are obtained. If the average cooling rate CR between 500 and 400 ° C. is 5 to 80 ° C./second, the microstructure is preferably controlled.

[Overaging process by box annealing (BAF-OA process)]
In the method for manufacturing a cold-rolled steel sheet according to this embodiment, BAF-OA is not performed. As described above, even if BAF-OA is not performed, the cold-rolled steel sheet of this embodiment has high strength, excellent press formability, and excellent non-St-St properties. If BAF-OA is performed by the method for manufacturing a cold-rolled steel sheet according to this embodiment, the solid solution C in the steel is reduced and the yield strength YP is less than 360 MPa. Therefore, BAF-OA is not performed in the method for manufacturing a cold-rolled steel sheet according to the present embodiment. In this embodiment, since BAF-OA is not performed, the productivity of cold-rolled steel sheets for drawn cans is significantly increased.

[Temper rolling process]
In the temper rolling process, an temper rolled steel sheet is manufactured by temper rolling (skin pass rolling) an annealed steel sheet that has not been over-aged after the annealing process at a cumulative reduction of 0.5 to 5.0%. . If the rolling reduction is less than 0.5%, the yield point elongation YP-EL may exceed 0% in the steel sheet after the accelerated aging treatment. If the rolling reduction exceeds 5.0%, the total elongation EL becomes less than 25%, and the press formability decreases. When the rolling reduction is 0.5 to 5.0%, excellent non-St-St properties and press formability can be obtained even after age hardening that occurs before processing such as drawing. The temper rolled steel sheet after the temper rolling process has a thickness of 0.15 to 0.50 mm.

[Plating process]
In the manufacturing method of the cold-rolled steel sheet according to the present embodiment, after the temper rolling process, Ni plating treatment, Ni diffusion plating treatment, Sn plating treatment, and TFS plating treatment are performed on the surface of the temper rolled steel plate (on the plate surface). At least one of the above may be implemented. In this case, a Ni plating layer, a Ni diffusion plating layer, a Sn plating layer, and a TFS plating layer (a plating layer composed of two layers of a metal Cr layer and a Cr hydrated oxide layer) are provided on the surface of the temper rolled steel sheet. At least one of which is formed. The Ni diffusion plating layer is formed by performing a diffusion heat treatment on a steel plate subjected to Ni plating.

It is possible to obtain a microstructure specific to the cold-rolled steel sheet according to the present embodiment by controlling each manufacturing condition in each step described above precisely and in combination. Specifically, the microstructure of the hot rolled steel sheet after the hot rolling process, the microstructure of the primary cold rolled steel sheet after the primary cold rolling process, the microstructure of the annealed steel sheet after the annealing process, and the tempering after the temper rolling process Only by controlling the microstructure of the rolled steel sheet for each process, a microstructure unique to this embodiment can be obtained. As a result, it is possible to obtain a cold-rolled steel sheet for a drawing can having high strength, excellent press formability, and excellent non-St-St properties.

Next, the effects of one aspect of the present invention will be described in more detail with reference to examples. However, the conditions in the examples are one example of conditions adopted to confirm the feasibility and effects of the present invention. The present invention is not limited to this one condition example. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

As a steelmaking process, slabs of steel types A to M were manufactured.

As a hot rolling process, these slabs were heated to 1200 ° C. and hot rolled to produce a 2.1 mm thick hot rolled steel sheet. The finishing temperature for hot rolling was 925 ° C. The coiling temperature CT of the hot-rolled steel sheet was as shown in Table 1.

As the primary cold rolling process, the hot rolled steel sheet was pickled and then subjected to primary cold rolling. In test numbers 1 to 19, primary cold-rolled steel sheets having a thickness of 0.25 mm were manufactured. In test number 20, a primary cold-rolled steel sheet having a thickness of 0.45 mm was manufactured. The cumulative reduction rate of the primary cold rolling was as shown in Table 1.

As an annealing process, CAL (continuous annealing) was performed on the steel sheet after the primary cold rolling process. Table 1 shows the average heating rate HR, the annealing temperature ST, and the average cooling rate CR between 500 and 400 ° C. At the annealing temperature ST, the steel sheet was soaked for 25 seconds. After soaking, gas cooling with nitrogen gas was performed. At this time, the steel plate was cooled without performing two-stage cooling from the annealing temperature ST to 50 ° C. (without holding the steel plate at an intermediate temperature). In gas cooling, the average cooling rate CR from 500 ° C. to 400 ° C. is as shown in Table 1, and the average cooling rate from 400 ° C. to 50 ° C. was 25 ° C./second.

The steel plate of test number 1 was further subjected to BAF-OA (overaging treatment by box annealing) after CAL. In BAF-OA, the steel sheet was soaked at 450 ° C. for 5 hours and then gradually cooled over 72 hours. Note that BAF-OA was not performed on steel sheets other than test number 1.

As the temper rolling process, temper rolling was performed on the steel sheet after the annealing process. The reduction ratio in temper rolling was 1.8% in all cases.

As the plating step, Ni plating treatment was performed on the steel plate of test number 8 shown in Table 1. Specifically, after the temper rolling process, Ni plating layers were formed on the front and back surfaces of the steel sheet by electroplating. The film thicknesses of the front and back Ni plating layers were both 2 μm. The steel plate of this test number 8 became a cold-rolled steel plate having a double-sided Ni plating layer.

Regarding the cold-rolled steel sheet produced as described above, the measurement results of the chemical components are shown in Table 2, and the observation results of the microstructure and the measurement results of the mechanical properties are shown in Table 3.

The microstructure was observed with an optical microscope at the L cross section of the manufactured cold-rolled steel sheet. The sample for structure | tissue observation was extract | collected from the center part of the width direction of the manufactured cold-rolled steel plate. The microstructure photograph was taken of a portion between 1/4 thickness in the thickness direction of the L cross section of a sample that had been polished and subjected to nital etching. Using the microstructure photograph, the average particle diameter of the ferrite was determined by the cutting method of JIS G0551 (2013).

In Table 2, “F + C” indicates that the microstructure mainly contains ferrite and granular cementite. “F + P” indicates that the microstructure mainly includes ferrite and pearlite. “XX” indicates that an unrecrystallized structure was observed. When an unrecrystallized structure was observed, the ferrite average particle size was not measured (because measurement was impossible).

Mechanical properties were measured by performing a tensile test using the manufactured cold-rolled steel sheet. 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 prepared 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 Z2241 (2011), yield strength YP, tensile strength TS, total elongation EL Yield point elongation YP-EL and yield ratio YR were determined.

The cold rolled steel sheets of test numbers 5, 7, 8, 11, 13, and 15 as examples of the present invention all satisfied the scope of the present invention in terms of manufacturing conditions, chemical composition, microstructure, and mechanical properties. As a result, these cold-rolled steel sheets have high strength, excellent press formability, and excellent non-St-St properties.

On the other hand, the cold rolled steel sheets 1 to 4, 6, 9, 10, 12, 14, and 16 to 20 that are comparative examples satisfy the scope of the present invention in terms of manufacturing conditions, chemical composition, microstructure, and mechanical properties. I didn't. As a result, these cold-rolled steel sheets could not simultaneously achieve strength, press formability, and non-St-St properties.

Test No. 1 is a conventional example in which BAF-OA was performed after CAL, but the C content was too low. Furthermore, the coiling temperature CT was too high. Furthermore, the annealing temperature ST of CAL was too high, which was a two-phase region temperature. Therefore, the microstructure was composed of ferrite and pearlite, the average grain size of ferrite exceeded 4.0 μm, and the yield strength YP was less than 360 MPa. Furthermore, the yield ratio YR was less than 80%.

In test numbers 2 to 4 and 18, although the production conditions were appropriate, the C content was too low. Therefore, the average particle diameter of the ferrite exceeded 4.0 μm, and the yield strength YP was less than 360 MPa. Furthermore, the yield point elongation YP-EL was higher than 0%, and stretcher strain was generated.

In Test Nos. 6 and 14, although the chemical composition was appropriate, the annealing temperature ST in CAL was too high and was a two-phase region temperature. Therefore, the microstructure was composed of ferrite and pearlite, and the average grain size of ferrite exceeded 4.0 μm. Therefore, the total elongation EL and / or the yield ratio YR was low, and the press formability was low. Furthermore, the yield strength YP of test number 6 was less than 360 MPa.

In Test No. 9, although the chemical composition was appropriate, the average cooling rate CR between 500 and 400 ° C. in CAL was too slow. Therefore, the yield strength YP was less than 360 MPa, and the yield ratio YR was less than 80%. This is probably because the cooling rate was too slow and the amount of dissolved C was too low.

In test number 10, although the chemical composition was appropriate, the average cooling rate CR between 500 and 400 ° C. in CAL was too fast. Therefore, the yield point elongation YP-EL was higher than 0%. Furthermore, the total elongation EL was less than 25%.

In test number 12, although the chemical composition was appropriate, the annealing temperature ST in CAL was too low. Therefore, an unrecrystallized structure remained in a part of the microstructure. As a result, the total elongation EL was as low as less than 25%, and the press formability was low.

In the test numbers 16, 17, and 19, the C content was too high. Therefore, the total elongation EL was too low as less than 25%, and the press formability was low.

In Test No. 20, the chemical composition was appropriate, but the cumulative rolling reduction in the primary cold rolling was too low. Therefore, the average particle diameter of the ferrite exceeded 4.0 μm, and the yield strength YP was less than 360 MPa. Furthermore, the yield point elongation YP-EL was higher than 0%, and stretcher strain was generated.

According to the above aspect of the present invention, it is possible to provide a cold-rolled steel sheet for a drawing can having high strength, excellent press formability, and excellent non-St-St properties without performing BAF-OA. This cold-rolled steel sheet is excellent in press formability, can suppress the occurrence of stretcher strain, and can be gauged down. Therefore, industrial applicability is high.

10: Ferrite 20: Granular cementite

Claims

A steel plate for a drawing can,
The steel sheet is in mass% as a chemical component,
C: more than 0.150 to 0.260%,
Sol. Al: 0.005 to 0.100%,
B: 0.0005 to 0.02%,
Si: 0.50% or less,
Mn: 0.70% or less,
P: 0.070% or less,
S: 0.05% or less,
N: 0.0080% or less,
Nb: 0.003% or less,
Ti: 0.003% or less,
And the balance consists of Fe and impurities,
The boron content and the nitrogen content in the chemical component are in mass% and satisfy 0.4 ≦ B / N ≦ 2.5,
The steel sheet has a microstructure,
A ferrite having an average particle size of 2.7 to 4.0 μm;
Including granular cementite and
The yield strength obtained from a tensile test in which the steel sheet is subjected to an aging treatment at 100 ° C. for 1 hour is parallel to the rolling direction is YP in unit MPa, the total elongation is EL in unit%, and the yield point. When the elongation is YP-EL in unit% and the yield ratio is YR in unit%,
YP is 360 to 430 MPa,
The EL is 25-32%,
The YP-EL is 0%;
A steel plate for a drawing can, wherein the YR is 80 to 87%.
The steel plate for a drawing can according to claim 1, wherein the EL is 27 to 32%.
The steel plate for a drawn can according to claim 1 or 2, wherein at least one of a Ni plating layer, a Ni diffusion plating layer, a Sn plating layer, and a TFS plating layer is disposed on the surface of the steel plate. .
It is a manufacturing method of the steel plate for drawn cans according to claim 1 or 2,
A steel making process for obtaining a slab having the chemical component;
The slab is heated to 1000 ° C. or higher, finish-rolled at 840 to 950 ° C., cooled after finish rolling, and wound at 500 to 720 ° C. to obtain a hot-rolled steel sheet,
A primary cold rolling step of obtaining a primary cold-rolled steel sheet by performing primary cold rolling with a cumulative rolling reduction of more than 80% on the hot-rolled steel sheet;
The primary cold-rolled steel sheet is heated at an average heating rate of 10 to 40 ° C./second, soaked within a temperature range of 650 to 715 ° C., and then an average cooling rate of 5 to 80 ° C. is applied between 500 and 400 ° C. An annealing process for obtaining an annealed steel sheet by carrying out continuous annealing cooled at a rate of 1 second / second,
A temper rolling step of temper-rolling the annealed steel plate that has not been over-aged after the annealing step at a cumulative reduction of 0.5 to 5.0% to obtain a temper-rolled steel plate. The manufacturing method of the steel plate for drawn cans characterized by these.
After the temper rolling step, the temper rolled steel sheet further includes a plating step of performing at least one of Ni plating treatment, Ni diffusion plating treatment, Sn plating treatment, and TFS plating treatment. The manufacturing method of the steel plate for drawn cans of Claim 4.