JP3257390B2 - Method for producing two-piece steel sheet with small in-plane anisotropy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a two-piece steel sheet having a small in-plane anisotropy.

[0002]

2. Description of the Related Art Steel plates for cans such as tin-plated steel plates having a tin-plated surface or tin-free steel (TFS) having been subjected to electrolytic chromic acid treatment are frequently used in food cans 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, and reduction of materials and manufacturing costs, mainly for beverage cans and the like, the transition from three-piece cans to two-piece cans and thinner can bodies have been carried out. Is being promoted.

[0004] In two-piece cans for food and beverage cans, squeezing is used.
DRD cans (Drawn and redr)
awn can), a DTR can (Drawn-thin-redrawn can) made by multi-stage drawing with thinning of the can body, and a DI can (Drawn) subjected to ironing after drawing.
and wall ironed can), but in each case,
At the time of can making, a cup-shaped can body is formed by drawing from a disc-shaped blank plate, or a cup-shaped can body with a smaller diameter and a deeper depth is formed by re-drawing from a cup-shaped can body. Including the step of:

[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 a neck wrinkle in the necking process in the subsequent process, but also causes the can body to be removed from the 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, DI can, DT
As for steel plates for R cans, from the viewpoint of weight reduction of can bodies and reduction of manufacturing cost in recent years, steel plates with thin gauges and further small in-plane anisotropy that can improve material yield have been strongly desired. It has become to.

Several techniques have been proposed as methods for producing a two-piece steel sheet having a small in-plane anisotropy.
For example, JP-A-2-141535 discloses that C: 0.
The hot rolling finish temperature of low carbon steel of 100 to 0.040% is Ar
A technique for reducing the temperature to less than ₃ transformation points has been proposed, and Japanese Patent Application Laid-Open No. 5-31245 has proposed a technique for rolling a low-carbon aluminum-killed steel and an ultra-low-carbon steel twice by rolling 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 latter technique, the in-plane anisotropy is reduced as compared with the conventional technique, but cold rolling and annealing are each performed by 2 times.
There is a problem in that it is necessary to perform the process every time, and the manufacturing cost of the steel plate increases.

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 0.23 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.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has been developed to provide a two-piece can steel sheet 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 manufacturing without using the same.

[0013]

The inventors of the present invention have conducted intensive studies on a method for producing a two-piece steel sheet for a two-piece can having a small in-plane anisotropy. It has been found that the in-plane anisotropy can be reduced economically and efficiently by adding B to the steel and optimizing the production conditions.

The present invention has been made based on such findings, and has a C content of 0.015 to 0.06 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: 0.003
5 wt%, O: 0.005 wt% or less, B: 0.000
2 to 0.002 wt%, B ≧ −0.02C +
A slab having a steel composition satisfying 0.0010 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 120 or more.
After cold rolling at a rolling reduction of 90%, the recrystallization temperature is higher than 7%.
Continuous annealing at a temperature of 50 ° C or less, and an elongation of 0.5%
An object of the present invention is to provide a method for producing a two-piece can steel sheet having a small in-plane anisotropy, wherein temper rolling of less than 3% is performed to a sheet thickness of 0.23 mm or less.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described specifically. 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 0.04 wt%,
N: 0.0020 to 0.0025 wt%, sol. A
l: 0.04 to 0.08 wt%, O: 0.0015 to
0.0040 wt%, B is not added, 0.0008
The ratio between the slab thickness and the hot-rolled finish thickness was changed variously for the three types of steel, wt% and 0.0012 wt%. After cold rolling at a cold pressure rate of 87%, continuous annealing and temper rolling were performed. And the earring rate were 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, an increase in the value of slab thickness / finished hot roll thickness slightly reduces the earring rate, but the change is small. On the other hand, the B-added steel has a smaller earring ratio than the B-free steel, and particularly when the value of slab thickness / finished hot-rolled thickness is 120 or more, the earring ratio is sharply reduced, and the B-added effect becomes remarkable. Was found.

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, paying attention to the cold rolling conditions, particularly the cold pressure ratio, the effect of adding B was examined. C: 0.02-
0.04 wt%, N: 0.0020 to 0.0025 wt
%, Sol. Al: 0.04 to 0.08 wt%, O:
0.0015 to 0.0040 wt%, B is not added,
And B: The ratio of the slab thickness to the hot-rolled finished thickness was 12 with respect to the steel added in the range of 0.0006 to 0.0015 wt%.
After hot rolling at 5 and cold rolling at various cold pressure ratios, continuous annealing and temper rolling were performed, and the earring ratio was measured. The result is shown in FIG.

In the case of B-free steel, the earring rate is minimized at a cooling pressure rate of about 87%, but the dependency on the cooling pressure rate is strong and the variation is large. On the other hand, the B-added steel has a smaller earring ratio than the B-free steel regardless of the cold pressure ratio. In particular, the earring rate is small and the variation is small in the range of the cooling pressure rate of 85 to 90%.

FIG. 3 is a diagram showing the results of measuring the earring ratio by melting steel sheets with various C and B contents. The ratio of the slab thickness to the hot-rolled finish thickness was 122, and the cold-pressure ratio was 86.5%. As is apparent from FIG.
0.015-0.06 wt%, B: 0.0002-0.
0020 wt% and B ≧ −0.02C + 0.0010
In the case of (%), the earring ratio becomes 3% or less, and the in-plane anisotropy becomes small.

Next, the composition of the present invention will be described. The steel sheet for two-piece cans of the present invention has a C of 0.015 to 0.06.
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:
0.0035 wt%, O: 0.005 wt% or less, B:
0.0002-0.002 wt%, and B ≧ −0.
02C + 0.0010 is satisfied.

C: C is an extremely important element for controlling in-plane anisotropy. When C is less than 0.015 wt%, the structure of the hot-rolled sheet tends to be coarsened. Therefore, even if B is added to control the slab thickness / finished hot-rolled thickness and the cooling pressure ratio, it is shown in FIG. As described above, it becomes difficult to reduce in-plane anisotropy. Further, even if Mn is added, it becomes difficult to obtain the required strength as a two-piece can. On the other hand, if the C content exceeds 0.06% by weight, the solid solution C
Since the amount, the amount of C segregated at the grain boundaries, and the amount of carbide increase, the deep drawability deteriorates, and as shown in FIG. Also deteriorates. Therefore, the C content is 0.015 to 0.0
The range is 6 wt%.

Si: Si is an element that remains in steel as an impurity even if not intentionally added, embrittles the steel sheet and deteriorates corrosion resistance. Further, when used as a base steel sheet for TFS, it also has an adverse effect on the electrodeposition of metallic Cr, 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 serves to prevent hot cracking of the slab by precipitating S in the steel as MnS, and to supplement the strengthening by C as a solid solution strengthening element. In order to precipitate and fix S, it is necessary to add 0.1 wt% or more. However, if it exceeds 0.6 wt%, the formation of texture is adversely affected and in-plane anisotropy is increased. Therefore, the Mn content is set in the range of 0.1 to 0.6 wt%.

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 the workability is deteriorated. The limit is 0.10 wt%. Therefore, so
l. The Al content is in the range of 0.02 to 0.1 wt%.

N: When N is large, even if Al and B are added, solid solution N tends to remain, which changes the texture and increases in-plane anisotropy. It is desirable to reduce as much as possible. From such a viewpoint, N
Is regulated to 0.0035 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 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,
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. In order to sufficiently exhibit the effect of adding B, when the amount of C is small, the grain size of austenite and ferrite tends to be large, so that a large amount of addition is required as compared with the case where the amount of C is relatively large. I do. As shown in FIG. 3, B ≧ 0.0002 wt% and B ≧
In the case of −0.02C + 0.0010 (wt%), 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 FIG. 3, when the B content exceeds 0.002%, the in-plane anisotropy increases. Therefore, while making the B content 0.0002 to 0.002 wt%,
The amount satisfies B ≧ −0.02C + 0.0010.

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 120 or more. The reason for setting the ratio of the slab thickness to the hot-rolled finished thickness to 120 or more is to sufficiently exert the effect of reducing the in-plane anisotropy by adding B as shown in FIG. If the ratio between the two is 120 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 cooling pressure ratio, respectively.

The reason why the hot rolling finishing temperature is 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.

The cold rolling after the hot rolling is performed in 8
It is performed at a rolling reduction of 5 to 90%. The cold pressure rate is an important condition for controlling the in-plane anisotropy, and as shown in FIG.
It must be 90%.

The subsequent recrystallization annealing is performed at a temperature not lower than the recrystallization temperature of 7
Perform at a temperature of 50 ° C. or less. If the temperature is lower than the recrystallization temperature, an unrecrystallized structure remains and in-plane anisotropy deteriorates. On the other hand, when the temperature exceeds 750 ° C., in the steel sheet having a thickness of 0.23 mm or less as in the present invention, the sheet thickness at the time of CAL passing after primary cold rolling is small, so that the CAL passing 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 continuous annealing, the steel sheet is finished to a predetermined thickness by temper rolling, and the elongation at that time is 0.5% or more and 3% or more.
Less than This is because shape control is difficult when the elongation is less than 0.5% or 3% or more.

The steel sheet finished in the final thickness as described above is thereafter subjected to various surface treatments such as tin plating, ultra-thin tin plating, tin-nickel plating, nickel plating, and chromium plating. 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.

[0040]

EXAMPLES (Example 1) Steels having the compositions shown in Tables 1 and 2 were melted in a converter,
A slab is formed 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 further temper rolling is performed to obtain a steel sheet having a predetermined thickness. And Table 3 shows the ratio of the slab thickness to the hot-rolled finished thickness, the cold rolling reduction, and the plate thickness at that time. The slab heating temperature was 1230 ° C., the finishing temperature was 870 ° C., and the winding temperature was 6 ° C.
The temperature was set to 20 ° C. and the annealing temperature was set to 650 ° C., and the overaging treatment was not performed. Further, the elongation rate of the temper rolling was 1.5%.

The thus manufactured steel sheet was measured for earring ratio. 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.

[0042]

[Table 1]

[0043]

[Table 2]

[0044]

[Table 3]

As shown in Table 3, it was confirmed that each of the steel sheets of the present invention had a low earring ratio and a small in-plane anisotropy. On the other hand, it was confirmed that the comparative examples outside the scope of the present invention had higher earring ratios and higher in-plane anisotropy than the present invention examples.

Example 2 Eight types of steel Nos. 5, 10, 14, 17, 21, 25, 27 and 34 in Tables 1 and 2 were melted in a converter and then continuously cast into slabs. The slab was hot-rolled, pickled, cold-rolled, then continuously annealed in a continuous annealing furnace, and then temper rolled to obtain a steel sheet having a predetermined thickness. Table 3 shows the ratio of the slab thickness to the hot-rolled finished thickness, the cold rolling reduction, and the plate thickness.
Shown in The slab heating temperature was 1150 ° C., the finishing temperature was 870 ° C., the winding temperature was 640 ° C., the annealing temperature was 700 ° C., and the overaging treatment was performed at 400 ° C. in a continuous annealing inline. Further, the elongation rate of the temper rolling was set to 1.0%. For the steel sheet thus manufactured, the earring rate was measured, and thereby the in-plane anisotropy was evaluated. Table 4 shows the results.
It is described together.

[0047]

[Table 4] As shown in Table 4, it was confirmed that all of the steel sheets of the present invention had lower earring ratios and lower in-plane anisotropy than the steel sheets of the comparative examples.

[0048]

As described above, according to the present invention,
It is possible to manufacture a two-piece steel plate for a two-piece can, such as a DRD can, a DI can, and a DTR can, which has a small in-plane anisotropy and a small decrease in yield due to the occurrence of ears, 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 change in an earring rate according to a cold pressure rate.

FIG. 3 is a view showing a relationship between C and B contents and an earring rate.

──────────────────────────────────────────────────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-53 -48913 (JP, A) JP-A-57-57835 (JP, A) JP-A-58-221263 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 38/00- 38/60

Claims (1)

(57) [Claims] 1. C: 0.015 to 0.06 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: 0.003
5 wt%, O: 0.005 wt% or less, B: 0.000
2 to 0.002 wt%, B ≧ −0.02C +
A slab having a steel composition satisfying 0.0010 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 120 or more.
After cold rolling at a rolling reduction of 90%, the recrystallization temperature is higher than 7%.
Continuous annealing at a temperature of 50 ° C or less, and an elongation of 0.5%
A method for producing a two-piece steel sheet having a small in-plane anisotropy, wherein a temper rolling of not less than 3% and a sheet thickness of 0.23 mm or less are performed.