JPS59113123A - Production of ultra-hard extra-thin cold rolled steel sheet - Google Patents

Abstract

PURPOSE:To produce an ultra-hard extra-thin steel sheet for can making having small intraplane anisotropy by setting the draft at the 2nd cold rolling at a specific value in the stage of subjecting a hot-rolled steel sheet of a continuously cast low carbon billet to two times of cold rolling having a recrystallization annealing stage to produce a cold-rolled steel sheet. CONSTITUTION:A continuously cast low carbon billet contg. <0.10% C, <0.06% Si, <0.5% Mn, <0.03% P, <0.03% S, <0.15% Al, <0.008% N is hot-rolled at a rolling finish temp. of 830-900 deg.C to a steel sheet, which is coiled at 580-730 deg.C. The hot-rolled steel sheet is pickled to remove surface scale and thereafter the steel sheet is subjected to the 1st cold rolling at a draft r1 and after the cold- rolled steel sheet is subjected to recrystallization annealing, the sheet is subjected to the 2nd cold rolling at a draft r2. The draft r1 in the 1st rolling and the draft r2 in the 2nd rolling are determined at the values of the relation satisfying the formulas ( I ), (II), whereby an ultra-hard extra-thin cold-rolled steel sheet for can making having small intraplane anisotropy is obtd.

Description

[Detailed description of the invention] The non-invention relates to a method for manufacturing ultra-hard, ultra-thin cold-rolled steel sheets.

In particular, the present invention relates to a method for manufacturing a cold-rolled steel sheet for small cans with in-plane anisotropy.

Conventionally, base sheets for ultra-thin steel sheets such as tinplate and tin-free casting sheets have been manufactured using the following two methods.

(a) A method of pickling after hot rolling, cold rolling, recrystallization annealing, and then finishing by skin pass rolling at a slight rolling reduction of 3% or less.

(b) After performing recrystallization annealing after the first cold rolling,
A method of finishing by performing a second cold rolling again at a high reduction rate of 50% or less. Materials produced by this method are usually D R (Do
It is called a material that can be used as a material.

The material properties conventionally required for cold-rolled steel sheets for cans produced by these methods will be explained. Since ancient times, food containers have mainly been made of so-called three-piece cans, consisting of three parts: a body, a main part, and a base. There is a so-called two-piece can. (, Gashi.

Conventionally, such two-piece cans are made of soft material with a thickness of 0.2 to 0.
Since a 4-piece thick can is used, it has the disadvantage of high manufacturing costs due to the thick plate, but on the other hand, a 2-piece can has excellent can functionality and high ironmaking efficiency. In recent years, this iron making method has been revised due to the advantage of having holes1.
It came. Among the two-piece cans, the DI can (Drawn)
anti-Wall Ironed Can) and DR
D Can 11) raw and Redrawn Can
), the manufacturing technology has progressed rapidly.

Regarding the materials used for these two-piece cans, for example, DRD cans were traditionally made with a plate thickness of about 0.2 to 0.3 tm, but recently, in consideration of economic efficiency, the plate thickness has been reduced. A method has been taken to compensate for the lack of strength due to this by increasing the hardness of the original plate.

A method to improve this strength is to perform recrystallization annealing after the first cold rolling, and then perform a second cold rolling, but the effect is still satisfactory. is not obtained. These problems will be explained below.

The drawability of ultra-thin steel sheets, which are generally used as raw materials for drawing cans, DRD cans, DI cans, etc., is similar to that of cold-rolled steel sheets for drawing used for automobile body parts. It is generally accepted that a large r value is desirable. For ultra-thin steel sheets that require large deep drawing processes, such as those made from Shikaji steel, even if the r-value is very high, wrinkles are likely to occur during the drawing process due to the thinness of the steel plate, and advanced deep drawing processes are required. It is difficult. Therefore, when producing deep cans, re-drawing and ironing are used in combination, so in reality ll-j is too thick fx.
The r value is not required, but rather the in-plane anisotropy △r of the so-called r value is small in order to reduce the amount of trimming and improve the material yield. Thin steel plate is required.

The r value is expressed as the ratio of the strain in the width direction to the strain in the thickness direction in a tensile test, and this r value varies depending on the direction in which the tensile test piece is taken. The degree of this anisotropy varies depending on the manufacturing method of the steel sheet.

On the other hand, the flange portion of the can after drawing shows anisotropy in the thickness distribution and height in the circumferential direction, but the sagging phenomenon occurs due to the in-plane anisotropy of the r value. In other words, the edges of the can rise higher in the direction of the larger r value, forming a peak, and the edges of the can become lower in the direction of the smaller r value, forming a valley. It is known that the r value and the Δr value are closely related to the texture of the crystal, and vary greatly depending on the following factors in the manufacturing process of the material. That is, (a) the rolling reduction ratio of cold rolling, (b) the hot rolling temperature before cold rolling, and (c) the precipitation behavior and dispersion of AtN fi precipitates during the recrystallization process. r value in crystal annealed state, △
The r value and texture have been discussed for a long time, and many manufacturing methods have been proposed.

However, regarding the manufacturing method of DR material used in the second cold-rolled state, which is the object of the present invention, there is still no disclosure of an effective force tearing method. As a result of extensive research into the manufacturing method of DR material with small selvage during deep drawing, the inventors of the present invention have previously filed a Japanese patent application No. 57-3307.
We disclosed this in Section 5 and were able to achieve our objective.

The purpose of the present invention is 1. Patent application No. 57-3 disclosed by the present inventors.
The object of the present invention is to further improve 3075 and provide an effective method for manufacturing a cold-rolled steel sheet for small cans with greater hardness and strength and in-plane anisotropy through simpler control during rolling.

The gist of the present invention is as follows.

That is, C: o, 1o% or less, Si
: 0.06% or less, Mn: 0.5% or less, r': o, o
3% or less, s:o, o3% or less, A/-: 0.15
% or less, N: 0.008% or less, with the remainder consisting of Fe and unavoidable impurities. , an ultra-hard, ultra-thin cold-rolled steel sheet comprising the steps of pickling the hot-rolled copper strip, subjecting it to a first cold rolling process, followed by recrystallization annealing, and then a second cold rolling process. In the manufacturing method, the rolling reduction rate r of the first cold rolling, (%)
and the rolling reduction ratio (r, i%) of the second cold rolling satisfy the following formulas (1) and (2), respectively.

60≦r, ≦79.9...(1)-0,
92r, +83≦r, ≦-0.75r, +98
・”(2) The experimental results of the present inventors that led to the present invention will be explained.

A low carbon aluminum killed steel slab having a chemical composition as shown in Table 1 was manufactured by a continuous casting method.

Table 1 A number of test material slabs having the chemical composition shown in Table 1 were
Both are hot-rolled at a finishing temperature higher than the Ars transformation point.
Hot-rolled steel strips with plate thicknesses of 1.2 wm and 2.4 mm were produced by winding in a temperature range of 0 to 700°C.

After descaling each of these hot rolled steel strip specimens.

After rolling with the first cold rolling at a rolling reduction ratio (r,) of 90% and 75%, recrystallization annealing is performed, and then the second cold rolling is performed at various rolling reduction ratios (r,). The cold-rolled steel sheets were each made with a thickness within the range of 0.12 to 0.3+m+1. After applying chromium plating to each sample material thus obtained and finishing it into a so-called tin-free steel plate, the height of the selvedge △H when carefully deep drawing a DRD can into a can with a haze diameter of 60- was measured. . In this case, the relationship between the Δl (and the rolling ratio of the first cold rolling) r and the rolling reduction ratio r2 of the second cold rolling is as shown in FIG.

The ear height ΔH(m) in FIG. 1 was calculated as follows. In other words, the peak of the ears of each sample material (1-
1p l and the height of the valley (Ht) are measured, and △Hi-Hp
-1-1i, △H measured for the common ear of each sample material
It is the average of i. Namely.

However, N: Number of ears In Figure 1, the solid line is r, = 90%, and the broken line is r, = 75.
% case. As is clear from Figure 1, △HHr
, and also the magnitude of the change. That is, r, -7
When it is as low as 5%, △H decreases as r increases,
r! becomes minimum in the range of 20 to 45% and increases again. However, if r is 90% and the first rolling reduction rate is 0.

△H does not change much until r is around 30%, and 30%
The number increases rapidly when it comes to dogs. Like this (r.

A new finding has been obtained that the ear height ΔH changes depending on the combination distribution of and r, and that it is possible to reduce ΔH by optimizing the distribution.

The present inventors based on the above new knowledge, rI and r! By combining these over a wider range, the height of the ears that occurs during deep drawing△
The results of measuring H are shown in FIG. Since it is desirable that ΔH be 1 ga or less as a practical limit for the ear height, the following evaluation was made in FIG.

○ mark; ΔH≦0.5 m Optimal range △ mark: 0.5 parrot <6851.0 m Good × mark: △H> 1. O basket
From the evaluation of △H shown in Figure 2, rl and r.

It was found that ΔH is good in the area narrowed between the straight line AB and the straight line IcD.

Straight line AB・r, =-0,75r, +98”・
(3) Straight line CD...-r1=-0,92r, +81
- This is expressed in (4). However, the rolling reduction r in Fig. 1,
is less than 60%, from equations (3) and (4) above, the second
Not only does the rolling reduction ratio (r) become large, making it difficult to straighten the shape of ultra-thin steel sheets, but also the hardness of the finished cold-rolled steel sheets increases, making it difficult to process them into cans. It should be limited to rl 560% (5).

In addition, the maximum rolling reduction r of the first cold rolling is limited by the capacity of the cold rolling mill, and it is not only difficult to achieve a high rolling reduction of more than 97.3%, but the production efficiency is significantly reduced. Therefore, it should be limited to r, ≦97.3% ·= (6).

Regarding the rolling reduction ratio r1 of the second cold rolling, see (3) above.
From equation (4), the stronger r is, the smaller r is. However, since recrystallization annealing is performed after the first cold rolling, the hardness is significantly smaller, and the hardness is extremely hard, which is the object of the present invention. Since the hardness of the ultra-thin cold rolled steel sheet cannot be guaranteed, the second cold rolling should be performed at a rolling reduction of at least 5% or more.

r! ≧5% ... (7) From formulas (3), (4), (5), (6), and (7) above, a good product can be obtained within the shaded area EFGHI in Figure 2. This is the relational range between rl and r2, and the range with a black frame within it is the optimal range of △■4≦0.5m. However, the inventors of the present invention
In 75, the rolling reduction ratio r during the first cold rolling was set to 80~
Since it was disclosed that it should be limited to 95%, in order to delete this range and obtain an even harder cold rolled steel sheet, r1
≦79.9%...(8), and by adding formula 5), it was decided to limit it to 60%≦r, ≦79.9%...(1).

Furthermore, (3) (from formula 43, the range in which the object of the present invention can be achieved is -0,92r, +81≦r,≦-0,75r, +
9 g ・(2) Equation (2) should be satisfied.

Therefore, it has been found that when formulas (]) and (2) are simultaneously satisfied, it is possible to obtain an ultra-thin cold-rolled steel sheet that is always super hard and has a selvedge height △H≦1 m during deep drawing.

(11) Next, the chemical composition of the material used in the present invention and the limiting conditions in hot rolling will be explained. First, the reason for limiting the chemical composition of the chain slab used in the present invention is as follows.

C: C is an important component that suppresses the growth of recrystallized grains during recrystallization annealing after the first cold rolling.

If the amount of Ci is increased, a steel plate with small grain size and high potassium tempering can be obtained, but if the amount of C exceeds 0.10%, the hardness becomes excessively high and deep drawability is inhibited. %
Limited to the following.

Si: Si degrades the corrosion resistance of glazed and tin-free steel sheets, etc., and also impedes workability during cold rolling, so less is better, and Mn should be at least 0.06% or less. Mn has a desulfurization effect. , and has the effect of preventing the occurrence of edge cracking in the hot rolled coil, but if the amount of S is small, excessive addition is economically undesirable and should be limited to 0.50% or less, which can prevent edge cracking.

(121' P: If P exceeds 0.03%, it hardens the material and further deteriorates the corrosion resistance of the thin steel sheet, so it was limited to 0.03% or less.

S: In relation to S and Mn, excessive content may cause edge cracks in hot-rolled coils and cracking defects during steelmaking due to an increase in MnS inclusions, so S is limited to 0.03% or less.

At: At acts as a strong deoxidizing agent, but if it exceeds 0.15%, recrystallized grain growth is suppressed.
% or less.

N: Nij mixes into molten steel from the air, and if excessive, hardens the material and impedes deep drawability, so it was limited to 0.008% or less.

In addition to the above-mentioned main limited composition, it is composed of Fe and unavoidable impurities.The melting method is not particularly limited, but the slab is usually manufactured by converter → vacuum degassing treatment and continuous casting.

Next, the reason for limiting the hot rolling conditions will be explained.

Slab heating temperature: 1100-1200 as rollability is inhibited in the case of
A range of 0.degree. C. is preferred.

Hot rolling finishing temperature: If the finishing temperature is too low, the occurrence of ears will be high, so it needs to be at least Ar, the transformation point or higher, and in the case of the material used in the present invention with the above composition, it is 830°C or higher. Should be. However, if the finishing temperature exceeds 900°C, the heating temperature of the slab needs to be high [2. Since energy will be wasted, the temperature range is limited to 830 to 900°C.

Winding temperature: If the winding temperature is as low as less than 580°C, the self-annealing effect will be small, and excessively high temperatures exceeding 730°C will make descaling during pickling difficult, so the temperature range is between 580 and 730°C. Limited.

Example 1 Low carbon aluminum killed trowel slabs having chemical compositions shown in Table 1 were produced by continuous casting method.
．． The hot-rolled steel strip had a thickness of 2 to 2.8%. After pickling and descaling the hot rolled steel strip, the first cold rolling is performed according to the present invention, and after recrystallization annealing, a second cold rolling is performed, and the cold rolled chain plate is chromium plated. A so-called tin-free steel plate was manufactured by applying this process, and this sample material was deep-drawn.
The ear height ζΔH was measured.

For comparison, hot-rolled steel strips with the same chemical composition are pickled and then the rolling reduction rl+r, which is outside the scope of the present invention! After performing the first and second cold rolling in the same manner, a tin-free steel plate was manufactured under the same conditions,
The results of measuring the ear height ΔH during deep drawing are shown in Table 2. Note that Table 2 shows the hardness of each sample material before chromium plating in terms of HR30T.

As is clear from the comparative test of the examples shown in Table 2, a hot rolled steel strip obtained by hot rolling a steel slurry (15) having a limited chemical composition according to the present invention under limited conditions was subjected to the first rolling process using the DR method. By performing cold rolling at a reduction rate r, recrystallizing it, and then performing a second cold rolling at a reduction rate r2, by limiting the relationship rI * rI. We are manufacturing ultra-hard, ultra-thin cold-rolled steel sheets that make it possible to reduce the selvedge height △H during deep drawing to less than 1 mm.
We were able to produce an ultra-hard, ultra-thin cold-rolled chain plate that can be drawn smoothly while avoiding the occurrence of "wrinkles".

[Brief explanation of drawings]

FIGS. 1 and 2 show that the first cold rolling reduction r is 75%, which was obtained through experiments to obtain the present invention. The second cold reduction rate r at 90%! Figure 2 is a correlation diagram showing the relationship between the selvedge height △H and the selvedge height △H due to a change in the combination of the first cold rolling reduction rate r1 and the second cold rolling reduction rate r. It is a correlation diagram showing the influence. Agent Patent attorney Takeo Nakaji (17) (16) Figure 1

Claims (1)

[Claims] (1) C: 0.10% or less, Si: 0.0 at weight ratio 1
6% or less, Mn 70.5% or less, P: 0.03% or less, S: 0.03% or less, At: 0.15% or less, N:
Continuously cast steel billets containing 0,00% or less and the remainder consisting of Fe and unavoidable impurities are rolled at a finishing temperature of 830 to 90%.
A process of hot rolling at 0°C and a coiling temperature of 580 to 730°C, and a second cold rolling process of the hot-rolled steel strip after pickling and stripping once, followed by recrystallization annealing. In a method for producing an ultra-hard, ultra-thin cold-rolled steel sheet that includes a step of rolling (-),
The rolling reduction ratio r of the first cold rolling (%) and the rolling reduction ratio r2 (%) of the second cold rolling are as follows (1), (
A method for producing an ultra-hard, ultra-thin cold-rolled steel sheet, characterized by satisfying Formula 21. 60≦r, ≦79.9 ... (]) -0,
92r, +s 1≦r2≦-0,75r, +98-
(2)