JP3407531B2 - Method for producing ultra-thin steel sheet for two-piece can with small in-plane anisotropy - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an ultra-thin steel sheet for a two-piece can having a small in-plane anisotropy. 2. Description of the Related Art Tin-plated steel sheets having tin-plated steel sheets or tin-free steel sheets (TFS) having been subjected to electrolytic chromic acid treatment are frequently used for food and beverage cans. . These cans and beverage cans are classified into three-piece cans and two-piece cans depending on the method of making the cans. In recent years, from the viewpoints of weight reduction of can bodies, omission of steps in can manufacturing, reduction of materials and manufacturing costs, mainly for beverage cans, etc., the transition from three-piece cans to two-piece cans and thinner can bodies have been carried out. Is being promoted. In addition, for steel plates for two-piece cans, there is a growing need for a gauge down of the steel plate itself as a material in order to further reduce the weight and cost of the can body. However, when the thickness of the steel sheet is reduced, the strength of the can body is reduced. Therefore, the steel sheet which has been subjected to the second cold rolling after the recrystallization annealing to have a high strength, that is, DR (Do
uble Reduce) materials are being used in steel sheets for two-piece cans. [0004] By the way, two-piece cans for food cans and beverage cans are provided with DRD cans (Draw cans) made by drawing and redrawing.
n and redrawn can), DTR cans (Drawn-thin-redrawn) made by multi-stage drawing with thinner can body
can) and DI which is ironed after drawing
There are cans (Drawn and wall ironed can), etc. In each case, a cup-shaped can body is formed by drawing from a disc-shaped blank plate during remanufacturing, or re-drawn from a cup-shaped can body. The method includes a step of forming a cup-shaped can body having a smaller diameter and a deeper depth by processing. [0005] During drawing in such a two-piece can making process, the height of the can end or the width of the flange is often reduced due to the in-plane anisotropy of the workability of the steel sheet. A so-called "ear" occurs that is non-uniform along the direction. These ears are trimmed and removed before necking of the end of the can. However, if the ears are large, the trim margin becomes large and the material yield decreases. Further, the ears cause fluctuations in the thickness distribution along the circumferential direction, which not only causes neck wrinkles during necking processing in a later step, but also causes the can body to be removed from a punch during DI processing. , Which may cause a punch-out defect, thereby lowering the material yield and lowering the quality. [0007] For these reasons, there is a demand for a steel plate for a two-piece can that has little ears during can-making, that is, a small in-plane anisotropy. In particular, D
Since the R material tends to have large ears, an ultrathin steel sheet for two-piece cans with much smaller in-plane anisotropy has been strongly desired. Several techniques have been proposed as methods for producing a two-piece steel sheet having a small in-plane anisotropy.
For example, Japanese Patent Application Laid-Open Nos.
JP-A-141536 discloses that C: 0.010 to 0.04.
A technique for reducing the hot rolling finish temperature of 0% low carbon steel to less than the Ar ₃ transformation point, and setting the slab heating temperature to less than 1100 ° C., and performing cold rolling and recrystallization annealing after cold rolling and recrystallization annealing. A technique has been proposed, and Japanese Patent Application Laid-Open No. 3-36215 discloses a method in which C is added to a low carbon steel of 0.006 to 0.02% by adding N to 0.1%.
002 to 0.015% in the range, the primary cold rolling reduction and the secondary cold rolling are 80 to 90% and 20 respectively.
Techniques for reducing the power to 50% have been proposed. Further, Japanese Patent Application Laid-Open No. Hei 5-31245 proposes a technique of rolling a low carbon aluminum killed steel and an ultra low carbon steel twice and annealing twice. However, even with the use of these techniques, it is difficult to satisfy the strict requirements for the generation of ears recently required for steel sheets for two-piece cans, and further improvements need to be made. In particular, in the technique of JP-A-5-31245, the in-plane anisotropy is reduced as compared with the conventional technique, but it is necessary to perform cold rolling and annealing twice each, which increases the manufacturing cost of the steel sheet. There is a problem that becomes. Japanese Patent Application Laid-Open Nos. 4-337049, 5-247669, and 7-62486 disclose techniques for adding B to steel plates for cans. All of these require that the microstructure be a two-phase structure composed of ferrite and martensite, bainite, or pearlite. Therefore, the C content is increased, and the annealing temperature is increased in the two-phase region, that is, at a high temperature of _one or more Ac. Need to be In the production of steel sheets for ultra-thin cans having a thickness of 0.20 mm or less, such high-temperature annealing is performed using CAL.
There is a problem that the threadability is remarkably deteriorated, and the productivity is reduced, that is, the production cost is increased. Further, due to the two-phase structure, workability and workability uniformity are fundamentally inferior to ferrite single-phase structure. Further, Japanese Patent Publication No. 55-34851,
Japanese Patent Application Laid-Open No. 6-306534 also discloses techniques for adding B, but these techniques merely add B for the purpose of softening, and any consideration is given to in-plane anisotropy. However, even if these techniques are used, the in-plane anisotropy cannot be sufficiently reduced. SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has been developed to provide an ultrathin steel sheet for a two-piece can having a small in-plane anisotropy, which can sufficiently satisfy recent demands. It is an object of the present invention to provide a method for economical production without reducing productivity. The inventors of the present invention have conducted intensive studies on a method of manufacturing an ultrathin steel sheet for a two-piece can having a small in-plane anisotropy. By adding B to the adjusted low-carbon steel and optimizing the production conditions, especially the ratio between the slab thickness and the hot-rolled finish, and the rolling reduction in the secondary cold rolling, economical and efficient in-plane differences can be achieved. It has been found that the anisotropy can be reduced. The present invention has been made based on these findings, and has a C content of 0.015 to 0.04 wt%,
i: 0.1 wt% or less, Mn: 0.1 to 0.6 wt%,
P: 0.02 wt% or less, S: 0.02 wt% or less, s
ol. Al: 0.02 to 0.1 wt%, N: 0.002
5 wt% or less , O: 0.005 wt% or less, B: (−
A slab having a steel composition containing 0.02C + 0.0010) to 0.002 wt% is hot-rolled so that the finishing temperature is Ar ₃ or more and the ratio of the slab thickness to the hot-rolled finished thickness is 125 or more. Then, after pickling, cold rolling is performed at a reduction rate of 83 to 88%, and then continuous annealing is performed at a temperature not lower than the recrystallization temperature and not higher than 750 ° C.
6Mn + 9 ≦ R2 ≦ 10 × log (B × 10 ⁴ ) +12
The present invention provides a method for producing an ultra-thin steel sheet for a two-piece can having a small in-plane anisotropy, wherein the sheet thickness is reduced to 0.20 mm or less by performing secondary rolling satisfying the following conditions. Hereinafter, the present invention will be described in detail. First, the basic concept and the experimental results that led to the completion of the present invention will be described. The present inventors have conducted various studies on the effect of B addition on in-plane anisotropy. First, attention was paid to the effect of hot rolling conditions. C: 0.02 to 0.03 t%, N:
0.0020 to 0.0025 wt%, sol. Al:
0.04 to 0.08 wt%, O: 0.0015 to 0.0
025 wt%, B is not added, 0.0008 wt%
% And 0.0012 wt%, the ratio of the slab thickness to the hot-rolled finish thickness is changed variously to obtain a cold pressure ratio of 86.
%, Cold-rolled, continuously annealed, and subjected to secondary rolling at a rolling reduction of 12% to finish the sheet thickness of 0.20 mm, and then the earring rate was evaluated. Here, the earring rate was used as a parameter of in-plane anisotropy. The earring ratio was obtained by deep drawing at a drawing ratio of 1.8, measuring the height of the ear, and expressing the value obtained by dividing the difference between the maximum value and the minimum value of the ear by the minimum value of the ear in percentage. The result is shown in FIG. In the case of B-free steel, there is almost no change in the earring ratio depending on the value of the slab thickness / the hot-rolled finish thickness, and the value is large. On the other hand, the B-added steel has a lower earring ratio than the B-free steel, and particularly when the value of the slab thickness / hot-rolled finish thickness is 125 or more, the earring ratio rapidly decreases,
It has been found that the effect of adding B is remarkable. Although the reason for this is not always clear at present, increasing the value of slab thickness / finished hot roll thickness causes the grains of the hot rolled sheet to become finer, and B tends to segregate at the austenite grain boundaries. B is also segregated at the ferrite grain boundaries after transformation. As a result, the texture after cold rolling and annealing changes due to the synergistic effect of grain refinement of the ferrite grains of the hot rolled sheet and the grain boundary segregation B. It is considered that the in-plane anisotropy was reduced. Next, the effects of the amounts of B and C were examined. FIG. 2 is a diagram showing the results of manufacturing steel sheets with various amounts of C and B and measuring the earring rate. The ratio of the slab thickness to the hot-rolled finish thickness is 139, and the cold pressure ratio is 86.
%, The secondary rolling reduction rate is 15%, and the sheet thickness is 0.195 m.
m. As is clear from the figure, the in-plane anisotropy is deteriorated if the B amount and the C amount are too large or too small. C:
0.015 to 0.04 wt%, B: (−0.02C +
It can be seen that the earring ratio is 4% or less when the content is 0.001) to 0.002 wt%, and the in-plane anisotropy is reduced. From these results, in the present invention, C: 0.015
0.04 wt%, B: (-0.02C + 0.0010)
０．００0.002 wt%. Further, the effects of the amounts of C, Mn, and B and the rolling reduction in the secondary rolling were examined. First, steel sheets having different amounts of C and Mn were manufactured at various secondary rolling reduction rates, and the earring rate and Vickers hardness Hv were measured. The result is shown in FIG.
Shown in FIG. 3 is a diagram showing the relationship between the (10C + Mn) amount on the horizontal axis and the secondary rolling reduction R2 on the vertical axis. Here, the amount of B is 0.0010 to 0.0015.
wt%, and the ratio of the slab thickness to the hot-rolled finished thickness is 129 to
138, the primary cold reduction rate was 85 to 88%, the secondary rolling reduction rate was 3 to 17%, and the plate thickness was finished to 0.19 to 0.20 mm. As apparent from FIG. 2, 10C + Mn =
0.25 (C: 0.015 wt%, Mn: 0.10 wt%
%) Or 10C + Mn = 1.0 (C: 0.04%)
(wt%, Mn: 0.60 wt%), the earring ratio exceeds 4%, and the in-plane anisotropy is poor. On the other hand, when the secondary rolling reduction R2 (%) is R2 =
When −6 (10C + Mn) + 9 = −60C−6Mn + 9, the Vickers hardness Hv of the steel sheet is less than 140, and the material strength required for securing the strength of the two-piece can cannot be obtained. This indicates that when C and Mn are small, it is necessary to increase the strength of the steel sheet by work hardening by secondary rolling. In the present invention, based on these results, the conditions for producing a steel sheet having sufficient material strength to secure the strength of the can body and having small in-plane anisotropy are as follows:
0.015 to 0.04 wt%, Mn: 0.1 to 0.6 w
t2, and the lower limit of the secondary rolling reduction R2 (%) is defined as a function of C and Mn. R2 = −60C−6Mn +
9 was defined. FIG. 4 shows that no B was added and B: 0.00
It is a figure which shows the change of the earring rate by the secondary rolling reduction of four types of steel plates of 04, 0.0008, and 0.0015 wt%. The B-free steel has a large earring ratio even when the secondary rolling reduction ratio is low, and the earring ratio increases with an increase in the rolling reduction ratio. On the other hand, the B-added steel has a smaller earring ratio than the B-free steel, and slightly increases depending on the amount of B added, but the increase in the earring ratio with the increase in the secondary rolling reduction is small up to about 20%. , 4% or less. However, even when B is added, the earring rate increases if the secondary rolling reduction rate becomes too large. Therefore, the relationship between the amount of B added, the secondary rolling reduction, and the earring rate was investigated in more detail. C:
0.036 wt%, B: 0.0003 to 0.002
A steel sheet with various changes of 3 wt% is manufactured under the conditions of a ratio of slab thickness to hot-rolled finished thickness of 139 to 147, a primary cold reduction rate of 84 to 88%, and a secondary rolling reduction rate of 10 to 28%. 0.2
It finished to 0 mm or less, and measured the earring rate. The result is shown in FIG. FIG. 5 is a diagram showing the relationship between the B content on the horizontal axis and the secondary rolling reduction R2 on the vertical axis. As shown in this figure, when the B content is increased, the earring rate is kept low even when the secondary rolling reduction is increased. By setting R2 ≦ 10 × log (B × 10 ⁴ ) +12, The earring rate can be reduced to 4% or less. The reason for this is not necessarily clear at present, but it is presumed that B segregated at the grain boundary has an effect of suppressing anisotropy deterioration due to secondary rolling. However, if the amount of B added is too small or too large, the earring ratio exceeds 4% regardless of the secondary rolling reduction, and the in-plane anisotropy cannot be sufficiently reduced. From these results, in the present invention, the secondary rolling reduction R2 (%) is set to R2 ≦ 1.
0 × log (B × 10 ⁴ ) +12. Next, the composition of the present invention will be described. The steel sheet for two-piece cans of the present invention has a C content of 0.015 to 0.04.
wt%, Si: 0.1 wt% or less, Mn: 0.1-0.
6 wt%, P: 0.02 wt% or less, S: 0.02 wt
% Or less, sol. Al: 0.02 to 0.1 wt%, N:
0.0025 wt% or less , O: 0.005 wt% or less,
B: (−0.02C + 0.0010) to 0.002 wt
% Steel composition. C: C is an extremely important element for controlling in-plane anisotropy. When C is less than 0.015 wt%, the grain structure of the hot-rolled sheet tends to be coarsened. Therefore, B is added to control the slab thickness / finished hot-roll thickness, the primary cold reduction ratio, and the secondary rolling reduction ratio. However, it is difficult to reduce in-plane anisotropy as shown in FIGS. Further, even if secondary rolling is performed by adding Mn, as shown in FIG.
v becomes less than 140, and it becomes difficult to obtain necessary strength as a two-piece can without deteriorating anisotropy. On the other hand, C
If the content exceeds 0.04 wt%, the amount of solid solution C in the ferrite grains, the amount of C segregated at the grain boundaries and the amount of carbides increase, so that the effect of adding B as shown in FIGS. Is not sufficiently exhibited, and the in-plane anisotropy is deteriorated. Therefore, the C content is in the range of 0.015 to 0.04 wt%. Si: Si is an element that remains in the steel as an impurity even if not intentionally added, embrittles the steel sheet and deteriorates the corrosion resistance. When used as a base steel sheet for TFS, it is a metal Cr. It also has an adverse effect on the electrodeposition of aluminum, so the smaller the content, the better. In the present invention, from the viewpoint of avoiding such adverse effects, the Si content is set to 0.1 wt% or less. Mn: Mn is used in order to prevent hot cracking of the slab by precipitating S in steel as MnS, to supplement the strengthening by C as a solid solution strengthening element, and to secure the strength of a two-piece can. It is a necessary element. In order to precipitate and fix S and secure the steel sheet strength and hardness, 0.1
Addition of not less than wt% is necessary, but if it exceeds 0.6 wt%, the formation of texture is adversely affected and the in-plane anisotropy is increased. Therefore, the Mn content is set to 0.1 to 0.6 wt.
% Range. P: P is a substitutional solid solution element like Mn, and has a greater strengthening ability than Mn, and is an effective element for increasing the strength of a steel sheet. It is an element that segregates and embrittles grain boundaries, and its content is preferably as small as possible. Further, the positive addition of P adversely affects the texture formation, resulting in an increase in in-plane anisotropy. Therefore, the P content is set to 0.02% by weight or less. S: S is desirably as small as possible from the viewpoint of preventing hot cracking of the slab, and is set to 0.02 wt% or less from such a viewpoint. sol. Al: sol. Al is added to precipitate N in steel as AlN. When the amount is less than 0.02 wt%, most of the added B forms BN, and the effect of reducing the in-plane anisotropy due to the addition of B is added. Is not fully exhibited. On the other hand, when a large amount of Al is added, Al ₂ O ₃ -based inclusions remain, and cracks due to inclusions are apt to occur at the time of can making, and workability is deteriorated. However, practically acceptable from the viewpoint of workability. The limit is 0.10 wt%. Therefore, so
l. The Al content is in the range of 0.02 to 0.1 wt%. N: In order to sufficiently exert the effect of the addition of B on in-plane anisotropy, it is desirable to minimize N as much as possible. When N is large, BN is easily formed even if the addition amounts of Al and B are adjusted appropriately, and the effect of adding B is weakened, resulting in an increase in in-plane anisotropy. From such a viewpoint, N is regulated to 0.0025 wt% or less. O: If a large amount of O is present in the steel, a part of the added B tends to form an oxide, and the effect of reducing the in-plane anisotropy due to the addition of B cannot be sufficiently exhibited. Also,
Oxide-based inclusions in the steel serve as starting points for the occurrence of cracks in the production of two-piece cans, and significantly impair workability. Therefore, it is desirable to minimize the total O amount. In the present invention, the total amount of O in steel is set to 0.0
Restrict to 05 wt% or less. B: B is the most important additive element in the present invention. By adding an appropriate amount of B, in-plane anisotropy can be effectively reduced. By controlling the ratio of the slab thickness to the hot-rolled finished thickness, B effectively segregates at the austenite grain boundaries during hot rolling, and makes the austenite grains of the hot-rolled sheet and the ferrite grains after transformation finer. Part of B forms BN, but other B also segregates at the ferrite grain boundaries of the hot rolled sheet after transformation. The synergistic effect of such hot-rolled sheet refinement and grain boundary segregation B affects the texture formation during recrystallization after cold rolling and exerts the effect of reducing in-plane anisotropy. Conceivable. Further, B segregated at the grain boundaries suppresses deterioration of anisotropy due to secondary rolling. In order to sufficiently exhibit the effect of adding B, it is necessary to add a larger amount of B than when the amount of C is relatively large, because when the amount of C is small, the grain size of austenite and ferrite tends to be large. There is. That is, FIG.
And as shown in FIG. 5, B ≧ −0.02C + 0.0
In the case of 01 (wt%), the effect of adding B is sufficiently exhibited, and the in-plane anisotropy is reduced. On the other hand, if B is added in an unnecessarily large amount, solid solution B remains not only in the grain boundaries but also in the ferrite grains, and it becomes easy to form a texture that increases in-plane anisotropy. As shown in FIGS. 2 and 5, when the B content exceeds 0.002%, the in-plane anisotropy increases. Therefore, the B content is (−0.02C + 0.00)
10) to 0.002 wt%. Next, the manufacturing conditions of the present invention will be described. In the present invention, after the steel having the above composition is melted from the converter, a slab is produced by continuous casting, and is subjected to hot rolling through rough rolling or by omitting rough rolling and directly inserting into a hot finishing mill. After pickling, cold rolling is performed, and then continuous annealing is performed in a continuous annealing furnace.
mm or less. The hot rolling is performed so that the finishing temperature is Ar ₃ or more and the ratio of the slab thickness to the hot rolled finished thickness is 125 or more. The ratio of the slab thickness to the hot-rolled finish thickness is set to 125 or more in order to sufficiently exert the effect of reducing the in-plane anisotropy by adding B as shown in FIG. If the ratio of the two is 125 or more, the slab thickness and the hot rolled finish thickness may be appropriately selected according to the final product sheet thickness and the optimum primary cold reduction rate and secondary rolling reduction rate, respectively. The reason why the hot rolling finishing temperature was set to Ar ₃ or more is that A
If finished below the r ₃ transformation point, a texture is formed in the hot-rolled sheet, crystal grains are coarsened, and in-plane anisotropy after cold rolling and annealing is deteriorated. The slab heating temperature and the winding temperature need not be particularly limited, and may be in the range usually performed. For example, the slab heating temperature is 1100 to 1250 ° C. and the winding temperature is 50.
It can be about 0 to 700 ° C. As described above, the cold rolling after the hot rolling is 8
It is performed at a rolling reduction of 3-88%. The primary cold pressure rate is an important condition for controlling the in-plane anisotropy together with the secondary rolling reduction rate to be described later. In order to stably reduce the in-plane anisotropy, the cold pressure rate is set to 83%. It needs to be ~ 88%. 83%
If it is less than or exceeds 88%, it becomes difficult to stably reduce the in-plane anisotropy even if the secondary rolling reduction is controlled. The subsequent continuous annealing is carried out at a recrystallization temperature of 75
Perform at a temperature of 0 ° C. or less. If the temperature is lower than the recrystallization temperature, an unrecrystallized structure remains and in-plane anisotropy deteriorates. Conversely, if the temperature exceeds 750 ° C., the steel sheet having a thickness of 0.20 mm or less as in the present invention has a small thickness at the time of the CAL threading after the primary cold rolling, so that the CAL sheeting property is significantly deteriorated. Troubles such as plate breakage and defective shape are likely to occur, and the productivity is reduced. Further, an austenite phase is generated during the soaking, and a hard low-temperature transformation phase is easily generated in a cooling process. Such an interface between the hard second phase and the ferrite matrix tends to be a starting point of cracking during can making, and deteriorates workability. The subsequent overaging process may or may not be performed. The effect of the present invention does not change when the overaging process is performed and when it is not performed. When performing the overaging treatment, any method of in-line OA in a continuous annealing furnace and batch OA by box annealing after continuous annealing may be used. After the continuous annealing, secondary rolling was further performed.
The plate is finished to a predetermined thickness of 20 mm or less, and the rolling reduction R2 (%) at that time is -60C-6Mn + 9 ≦ R2 ≦ 10 × l
og (B × 10 ⁴ ) +12. R2 is -60C-6
If it is less than Mn + 9, the Vickers hardness Hv of the steel plate is less than 140, and the material strength necessary for securing the strength of the two-piece can cannot be obtained. On the other hand, as shown in FIGS. 4 and 5, R2 is set to 10 × log (B × 10 ⁴ ) +
In the case of 12 or less, the earring rate can be 4% or less. The steel sheet thus finished to the final thickness is then subjected to various surface treatments such as tin plating, ultra-thin tin plating, tin-nickel plating, nickel plating, chromium plating and the like. In particular, when such a surface-treated steel sheet is used for a DI can, a no-reflow tin-plated steel sheet is desirable, and a film laminated steel sheet for a DTR can,
When used as a base steel sheet of a precoated steel sheet, an electrolytic chromic acid-treated steel sheet, that is, TFS, is most desirable from the viewpoint of working adhesion. These surface-treated steel sheets can be used alone or as a film-laminated steel sheet obtained by laminating a resin film such as polyester or a pre-coated steel sheet coated with a paint such as epoxy. EXAMPLES Example 1 Steels having the compositions shown in Tables 1 and 2 were melted in a converter,
A slab is produced by continuous casting, hot rolling is performed on the slab, pickling is performed, cold rolling is performed, then continuous annealing is performed in a continuous annealing furnace, and then secondary rolling is performed to obtain a steel sheet having a predetermined thickness. And In this case, the ratio of the slab thickness to the hot-rolled finish thickness, the value of -60C-6Mn + 9, and 10 × log (B ×
Table 3 shows the value of 10 ⁴ ) +12, the secondary rolling reduction, and the sheet thickness. The slab heating temperature was 1230 ° C and the finishing temperature was 8
70 ° C, winding temperature 620 ° C, primary cold pressure rate 83-88%,
The annealing temperature was 650 ° C. The earring ratio of the steel sheet manufactured as described above was measured. The earring rate is 1.8
The ear height was measured after the deep drawing, and the difference between the maximum value and the minimum value of the ear was expressed as a percentage obtained by dividing the difference by the minimum value of the ear, thereby evaluating the in-plane anisotropy. The results are also shown in Table 3. [Table 1] [Table 2] [Table 3] As shown in Table 3, it was confirmed that each of the steel sheets of the present invention had a small earring ratio of 4% or less and a small in-plane anisotropy. On the other hand, a comparative example outside the scope of the present invention has a larger earring ratio than the inventive example,
It was confirmed that the in-plane anisotropy was large. (Example 2) Five types of steel Nos. 5, 10, 14, 21, and 31 in Tables 1 and 2 were melted from a converter and then continuously cast into slabs. Rolling was performed, after pickling, cold rolling was performed, then continuous annealing was performed in a continuous annealing furnace, and secondary rolling was performed to obtain a steel sheet having a predetermined thickness. In this case, the ratio of the slab thickness to the hot-rolled finish thickness, the value of -60C-6Mn + 9, 10 × log
Table 4 shows the value of (B × 10 ⁴ ) +12, the primary cooling pressure ratio, the annealing temperature, the secondary rolling reduction ratio, and the plate thickness. The slab heating temperature was 1150 ° C., the finishing temperature was 870 ° C., and the winding temperature was 660.
° C. The steel sheet thus manufactured was measured for the earring rate, and the in-plane anisotropy was evaluated. In addition, Vickers hardness was measured. Hardness is H ≧ 14
If it is 0, the strength of the can body can be secured, so that Hv <14
0 was x, and Hv ≧ 140 was ○. Table 4 shows the results.
It is described together. [Table 4] As shown in Table 4, it was confirmed that each of the steel sheets of the present invention had a smaller earring ratio and a smaller in-plane anisotropy than the steel sheets of the comparative examples. Further, in the examples of the present invention, the hardness of the steel sheet was Hv ≧ 140, and it was confirmed that the strength of the can was sufficiently secured. As described above, according to the present invention,
Ultra-thin steel sheets for two-piece cans, such as DRD cans, DI cans, and DTR cans, which have low in-plane anisotropy and low yield reduction due to ear generation, can be manufactured without lowering productivity. Therefore, it is possible to reduce the manufacturing cost of the two-piece can.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a change in an earring ratio depending on a slab thickness / a hot-rolled finish thickness. FIG. 2 is a diagram showing a relationship between C and B contents and an earring rate. FIG. 3 is a view showing the relationship between the (10C + Mn) amount, the secondary rolling reduction, the earring rate, and the Vickers hardness Hv. FIG. 4 is a diagram showing a change in an earring ratio with respect to a secondary rolling reduction ratio depending on a B content. FIG. 5 is a diagram showing a relationship between a B content, a secondary rolling reduction ratio, and an earring ratio.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Takashi Awaya 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Inside Nippon Kokan Co., Ltd. (56) References JP-A-64-15327 (JP, A) JP-A-9 −241756 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C21D 9/48 C21D 8/04 C22C 38/00 301 C22C 38/06

Claims (1)

(57) [Claims 1] C: 0.015 to 0.04 wt%, S
i: 0.1 wt% or less, Mn: 0.1 to 0.6 wt%,
P: 0.02 wt% or less, S: 0.02 wt% or less, s
ol. Al: 0.02 to 0.1 wt%, N: 0.002
5 wt% or less , O: 0.005 wt% or less, B: (−
A slab having a steel composition containing 0.02C + 0.0010) to 0.002 wt% is hot-rolled such that the finishing temperature is Ar ₃ or more and the ratio of the slab thickness to the hot-rolled finished thickness is 125 or more. Then, after pickling, cold rolling is performed at a reduction rate of 83 to 88%, then continuous annealing is performed at a temperature of not less than the recrystallization temperature and not more than 750 ° C, and the reduction rate R2 (%) is −60C−
6Mn + 9 ≦ R2 ≦ 10 × log (B × 10 ⁴ ) +12
A method for producing an ultra-thin steel sheet for a two-piece can having a small in-plane anisotropy, comprising performing a secondary rolling that satisfies the following: