JPH09184018A - Manufacture of high strength steel sheet for vessel, reduced in inplane anisotroty - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the manufacturing method for reducing the inplane anisotropy of a high strength steel sheet for vessel, having >=65 hardness by HR30T. SOLUTION: A slab of a steel, having a composition consisting of, by weight, 0.008-0.08% C, <=0.06% Si, <=0.8% Mn, <=0.03% P, <=0.03% S, <=0.15% sol.Al, <=0.008% N, and the balance Fe with inevitable impurities, is hot-rolled at a rolling finishing temp. not lower than the Ar3 transformation point, coiled at <=730 deg.C, and descaled. The resultant steel plate is subjected to primary cold rolling satisfying inequality 70<=CR<=83-3.3log(Cwt.%), to recrystallization annealing, and then to secondary cold rolling satisfying either of the following inequalities: in the case of 70<=CR<80, 10<=DR<=30; in the case of CR>=80, 10<=DR<=9.2(91.5-CR) -675(Cwt.%) and DR<=30. In the above inequalities, CR means the draft (%) at the primary cold rolling and DR means the draft (%) at the secondary cold rolling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a steel sheet for containers having high strength and excellent in-plane anisotropy, and in particular,
Hardness of HR30T is 65 or more, DRD can (Drawn and
The present invention relates to a method for producing a steel plate for a high-strength container, which is suitable as a redrawn can material.

[0002]

2. Description of the Related Art Tinplate and TFS (Tin Free Steel) original plates are roughly classified into the following two types. (1) After recrystallization annealing, T1-T6 (JIS G330) that is finished by temper rolling at a slight reduction (about 3% or less)
3 Rockwell T hardness (HR30T) 46-73),
(2) DR material (Double Reduced Mater) finished by re-rolling annealing and then cold rolling again at high pressure reduction rate (50% or less)
ial) DR material is also DR-8 (HR3
0T: 73), DR9 (same: 76), DR-9M (same:
77) and DR-10 (same as: 80).

In the field of food cans using these materials, so-called two-piece cans, in which the top part is joined to a cup having a body and a bottom integrally formed, have been widely used in recent years. The reason is that the can function is excellent and the can manufacturing efficiency is high. Among the two-piece cans, DI cans (Drawn and Wall Ironed Can) and DRD cans (Drawn and Redrawn Can) can be used. The manufacturing technology of has advanced rapidly. As a result, as a material for DRD cans, a material having a temper of T-4 T-5 and a plate thickness of 0.2 to 0.3 mm has been conventionally used, but recently, from the economical aspect, the plate thickness is reduced. A method is adopted in which the strength of the original plate is used to make it thinner and compensate for the lack of strength. Thus, as a typical technique for increasing the strength of the original plate for DRD cans, the second cold rolling after recrystallization annealing as shown in JP-A-58-151426.
A method of performing (secondary cold rolling) has been proposed.

Now, as a characteristic required for this DRD can, it is desirable that the r value is large as in the case of a drawing steel sheet for automobiles. However, an ultra-thin steel sheet that requires a large drawing process, even if the r value is very large, is thin and easily wrinkles during the drawing process, making it difficult to perform deep drawing. Therefore, in the case of a deep container, methods such as ironing and redrawing are taken, and in practice, a large r value is not necessary. Rather, it is important that the occurrence of ears is small in order to reduce the trimming allowance and improve the yield. As an index of this ear, Δr Δr = (r ₀ + r ₉₀ −2r ₄₅ ) / 2 r ₀ indicating the anisotropy of the r value: r value in the rolling direction r ₉₀ : in the direction forming a 90 ° inclination with the rolling direction r value r ₄₅ : The r value in the direction forming an inclination of 45 degrees with the rolling direction is used.

[0005]

However, the technique for strengthening the strength disclosed in Japanese Patent Laid-Open No. 58-151426 is a method of increasing the reduction ratio of the secondary cold rolling, which causes a problem of increasing Δr negatively. was there. Then, the objective of this invention is to establish the manufacturing technique for reducing the in-plane anisotropy of the steel plate for high strength containers. Further, a specific object of the present invention is that the hardness satisfies HR30T of 65 or more,
In addition, it is to establish a manufacturing technology of a steel sheet for a high strength container having a small in-plane anisotropy of Δr of ± 0.2 or less.

[0006]

[Means for Solving the Problems] In order to achieve such an object, the inventors have made earnest studies on manufacturing conditions, especially rolling conditions, which affect the in-plane anisotropy of r value of a low carbon steel sheet.
As a result, the findings newly found by the inventors are:
Δr decreases monotonically with the reduction ratio of the secondary cold rolling, and the reduction ratio is almost constant regardless of the C content. Therefore, in order to bring the temper to the target hardness or higher, a certain amount of secondary cold rolling must be performed, but as described above,
Since Δr decreases due to the next cold rolling, after recrystallization annealing
The upper limit of the reduction ratio of the secondary cold rolling has to be set according to the target Δ r, and if the secondary cold rolling is performed further, the ear becomes large and it becomes unsuitable as a DRD can. On the other hand, r after annealing
The value, Δr, depends on the carbon content and the primary cold rolling reduction. For this reason, it is necessary to determine the primary cold rolling reduction and the secondary cold rolling reduction according to the amount of carbon. Considering that a certain degree of reduction in secondary cold rolling must be taken in order to obtain a high-strength steel sheet, it is necessary to reduce the reduction rate in primary cold rolling as compared with the conventional case.

The present invention has been completed on the basis of the above findings, and its gist structure is as follows. C: 0.008 to 0.08 wt%, Si: 0.06 wt% or less, Mn: 0.8 wt%
% Or less, P: 0.03 wt% or less, S: 0.03 wt% or less, sol A
A steel slab containing l: 0.15 wt% or less, N: 0.008 wt% or less, and the balance of Fe and unavoidable impurities is hot-rolled at a rolling end temperature of Ar ₃ transformation point or higher at 730 ° C.
After winding and descaling as follows, primary cold rolling satisfying the following formula (1) was performed, recrystallization annealing was performed, and
A method for producing a steel sheet for a high-strength container having a small in-plane anisotropy, which comprises performing a secondary cold rolling satisfying the formula (2) or the formula (3). Note 70 ≦ CR ≦ 83-3.3 log (Cwt%) (1) When 70 ≦ CR <80 10 ≦ DR ≦ 30 (2) When CR ≧ 80 10 ≦ DR ≦ 9.2 ( 91.5-CR) -675 (Cwt%), and DR ≦ 30 (3) However, CR: primary cold rolling reduction (%) DR: secondary cold rolling reduction (%)

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the steel composition and manufacturing conditions in the present invention will be described below. C: 0.008 to 0.08 wt% C is an important component that suppresses the growth of recrystallized grains. C
If the content is increased, the crystal grains will become finer and a high degree of tempering will be obtained. However, if added excessively, the workability deteriorates,
Cold rolling deteriorates due to hardening. Therefore, the C content is 0.008 wt% to 0.08 wt%, preferably 0.012 to 0.05
wt% range.

Si: 0.06 wt% or less Si lowers the corrosion resistance of tin plate and extremely hardens the material to prevent cold rolling. Therefore, 0.06 wt% or less, preferably 0.
It should be less than 03wt%.

Mn: 0.8 wt% or less Mn is an element useful as MnS for promoting de-S and preventing hot cracking. Further, since the transformation point is lowered, rolling is likely to be completed at the transformation point or higher during hot rolling, which is a preferable element from the viewpoint of securing the material. However, excessive addition brings about a risk that the hot-rolled sheet is transformed into a hard structure. Therefore, the addition amount is 0.8 wt% or less.

P: 0.03 wt% or less P is an element that hardens the material like Si and reduces the corrosion resistance of tinplate. Therefore, the P content is 0.03 wt% or less.

S: 0.03 wt% or less S is an element that causes ear cracking of the coil during hot rolling. Further, when the S content is increased, inclusions such as MnS are increased, which causes a decrease in local ductility. Therefore, it is necessary to limit the S content to 0.03 wt% or less.

Sol Al: 0.15 wt% or less sol Al is an element necessary for deoxidation, but if it is added in excess of 0.15 wt%, not only the deoxidizing effect will be saturated, but also inclusions will be generated, resulting in moldability. Adversely affect. Therefore, the content of sol Al should be 0.15 wt% or less.

N: 0.008 wt% or less N is an impurity element that is unavoidably mixed in the steel.
Excess N hardens the material, so the upper limit is made 0.008 wt%.

Next, manufacturing conditions will be described. The end temperature of hot rolling is set to an Ar ₃ transformation point or higher, and the lower limit temperature needs to be changed according to the Ar ₃ transformation point. The end of hot rolling
Below the Ar ₃ transformation point, two-phase rolling occurs, and a texture that adversely affects the r value of the annealed material develops, resulting in a high ear rate. Further, the coiling temperature after completion of hot rolling needs to be 730 ° C. or lower. If this temperature is exceeded, the influence of the winding temperature on Δr will increase,
Further, the hot-rolled sheet is softened and the reduction ratio of the secondary cold rolling must be increased in order to obtain the target hardness of the final product, which is not preferable from the viewpoint of maintaining the in-plane anisotropy. If the coiling temperature is too low, the precipitation of AlN, etc. will not be sufficient.
Since lowering of the value is caused, it is preferable to set the lower limit to 500 ° C.

The reduction ratio of the primary cold rolling is 70≤CR≤8.
3-3.3 log (Cwt%), but CR: primary cold rolling reduction (%) must be performed in the range. This relationship is shown in FIG. That is, considering the plate thickness of the tin plate and the thickness of the hot-rolled plate that can be manufactured, the primary cold rolling reduction cannot be less than 70%. On the other hand, if the high-pressure reduction ratio is excessively high, the plate can be thinned, but Δr becomes negatively large after recrystallization annealing, and further, when secondary cold rolling is performed, the value becomes negatively large. Since this tendency becomes stronger as the carbon amount increases, the upper limit of the reduction rate in the primary cold rolling must be a function of the carbon amount.

Continuous annealing is desirable as the annealing after the primary cold rolling. The annealing temperature in that case is 670 so that the recrystallization is completed.
It is preferably in the range of ℃ to 750 ℃.

The secondary cold rolling performed after the primary cold rolling and annealing is performed within the range of the rolling reduction determined by the following formula according to the rolling reduction of the primary cold rolling. Reduction ratio of primary cold rolling CR
Is in the range of 10 ≦ DR ≦ 30 when 70 ≦ CR <80, and 10 ≦ DR ≦ when CR ≧ 80.
9.2 (91.5-CR) -675 (Cwt%), and D
It is performed in the range of R ≦ 30. However, CR: primary cold rolling reduction (%), DR: secondary cold rolling reduction (%)

That is, in any case, in order to obtain the target hardness, it is necessary to give a reduction rate of 10% or more in the secondary cold rolling. However, the secondary cold rolling is 4
Since the r value in the 5 degree direction tends to be relatively large and the ear rate tends to be large, it is necessary to set an upper limit value. As described above, since the rate of change of Δr due to the secondary cold rolling is constant regardless of the carbon content, the Δr of the material before the secondary cold rolling (after the recrystallization annealing) and the secondary cold rolling are performed. Δr depending on the rolling reduction of
Is determined. Here, the Δr value after the recrystallization annealing is determined by the reduction ratio and the carbon amount of the primary cold rolling as shown in FIG. 2 (other manufacturing conditions are the same as in Table 2). As shown in FIG. 2, 70 ≦
When CR% <80, Δr hardly changes, but when 80% or more, Δr suddenly decreases.
It can be seen that the value of the reduction rate that decreases depends on the amount of carbon. Therefore, the reduction ratio (CR) of the primary cold rolling is 70 ≦.
When CR% <80, the reduction ratio (D
Although the upper limit of R) is 30%, when the reduction ratio of the primary cold rolling is 80% or more, the upper limit value of the reduction ratio of the secondary cold rolling is as follows. It must be a function of the reduction ratio of the primary cold rolling.

[0020]

EXAMPLES A method for manufacturing a steel sheet for high strength containers according to the present invention will be described based on examples. After the steel having the chemical composition shown in Table 1 was melted, it was hot-rolled under the conditions shown in Table 2, wound, descaled by pickling, re-crystallized by primary cold rolling and continuous annealing. Annealing and secondary cold rolling are performed and No. 1 to 10 are tinted, and No. 11 to 20 are TFS.
Finished.

[0021]

[Table 1]

[0022]

[Table 2]

A test piece was taken from the obtained steel sheet, and hardness and r value were measured. Further, Δr was calculated by the above-mentioned formula. However, r of high-strength DRD material subjected to secondary cold rolling
Regarding the value, it is not possible to obtain the r value by the ordinary tensile test method, so the value of Contorol Products (USA)
Obtained using Module Drawability Tester. This is r
Since it has been empirically found that there is a correlation between the value and the Young's modulus, the Young's modulus is determined by the “magnetic vibration method”, and the r-value is calculated from the statistical analysis of the measurement results of the r-value and Young's modulus. It is what I want.

Table 2 shows the measured characteristic values. It should be noted that FIG. 3 shows Δr obtained by the above method for an ordinary tin-plated steel plate.
And the ear rate ΔH (refer to FIG. 4 for the definition of the ear rate) actually measured by squeezing the cup. From this, it was confirmed that there is a good correlation between ΔH and Δr. Further, FIG. 5 shows that after recrystallizing annealing a steel sheet obtained by rolling two kinds of steels having different carbon contents at a primary cold rolling reduction of 86%,
The relation between DR and Δr when the secondary cold rolling reduction ratio is variously changed (other manufacturing conditions are the same as in Table 2) is shown. Table 2
Therefore, the steel plate manufactured by the method of the present invention has a hardness of HR.
It satisfies 65 or more at 30T and the in-plane anisotropy Δr is ± 0.
You can see that it is as small as 2. On the other hand, the comparative method No. in which the component composition, the primary cold rolling reduction rate, the secondary cold rolling reduction rate, or the hot rolling condition was out of the range of the method of the present invention
It can be seen that HR30T hardness of Nos. 1, 5, 7, 8, 9, 10, 13, 14, 15, and 20 is less than 65, or the in-plane anisotropy Δr exceeds ± 0.2.

[0025]

As described above, according to the method of the present invention, since the in-plane anisotropy Δr can be improved to within ± 0.2, it is possible to reduce the occurrence of ears during press molding and to perform trimming. The yield can be improved by reducing the cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the primary cold rolling reduction and the C content in the present invention.

FIG. 2 is a graph showing the relationship between in-plane anisotropy Δr before primary cold rolling, primary cold rolling reduction, and C content.

FIG. 3 is a graph showing the relationship between ear rate ΔH and anisotropy Δr.

FIG. 4 is a diagram showing the definition of ear rate ΔH.

FIG. 5 is a graph showing the relationship between in-plane anisotropy Δr and reduction ratio of secondary cold rolling.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiyuki Kato 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Prefecture Technical Research Institute, Kawasaki Steel Co., Ltd. (72) Satoru Sato 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Kawasaki Chiba Steel Works, Ltd.

Claims (1)

[Claims] 1. C: 0.008 to 0.08 wt%, Si: 0.06 wt% or less, Mn: 0.8 wt% or less, P: 0.03 wt% or less, S: 0.03 wt% or less, sol Al: 0.15 wt% or less, N : A steel slab containing 0.008 wt% or less and the balance Fe and unavoidable impurities is hot-rolled at a rolling end temperature of Ar ₃ transformation point or higher, wound at 730 ° C or lower, and descaled. After doing
In-plane anomaly characterized by performing primary cold rolling that satisfies the following formula (1), performing recrystallization annealing, and performing secondary cold rolling that satisfies the following formula (2) or (3) A method for manufacturing a steel sheet for a high-strength container, which has a low degree of orientation. Note 70 ≦ CR ≦ 83-3.3 log (Cwt%) (1) When 70 ≦ CR <80 10 ≦ DR ≦ 30 (2) When CR ≧ 80 10 ≦ DR ≦ 9.2 ( 91.5-CR) -675 (Cwt%), and DR ≦ 30 (3) However, CR: primary cold rolling reduction (%) DR: secondary cold rolling reduction (%)