JPH05171285A - Production of extremely soft steel sheet for vessel reduced in low anisotropy and having ageing resistance - Google Patents

Abstract

PURPOSE:To save energy, to reduce manufacture days and to improve labor productivity by subjecting a steel with a specific composition to rolling at respectively specified temp. and draft, to cooling at specific velocity, to rolling at respectively specified temp. and draft, and then to coiling. CONSTITUTION:The steel has a composition consisting of, in weight ratio, <=0.0015% C, <=0.005% N, <=0.3% Al, 0.1-1.0%, in total, of one or more elements among Mn, Si, Ni, Cu, Cr, and P, and the balance Fe with inevitable impurities and where Mn/S is regulated to >=5 and also the relationship between coiling temp. CT( deg.C) and nitrogen content N(%) satisfies an inequality. This steel is rolled at a temp. between Ar3 and (Ar3+100 deg.C) and at >=50% total draft. Subsequently, cooling is performed at 10 deg.C/sec average cooling rate at the time of gamma alphatransformation. Then, the steel is rolled at <=Ar3 at =35% draft, coiled at 750-600 deg.C, pickled, cold-rolled, and continuously annealed. By this method, the occurrence of earing can be prevented, and production yield can be improved.

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 plate for a soft container such as an extremely soft tin plate or tin-free steel which has a small anisotropy and an excellent stretcher strain resistance.

[0002]

2. Description of the Related Art In recent years, a method of producing a steel sheet for a soft container having a temper of T-3 or less by continuous annealing has been studied. For example, Japanese Examined Patent Publication No. 63-10213 discloses a method for producing a steel sheet for a soft container from a low carbon aluminum killed steel having a specific component by continuous annealing with overaging treatment. The gist of this publication is that N is fixed in the form of AlN with Al, and C is fixed in the form of cementite by overaging treatment to impart aging resistance, and skin pass rolling is relatively mild. However, it is difficult to achieve the temper T-1 and T-2. Therefore, box annealing is indispensable for manufacturing T-1 and T-2. As a method of manufacturing a soft container material, it is considered to highly refine the steel, but it is known that coarsening of the hot-rolled sheet occurs with the high purification of the steel, in which case ridging may occur. is there. When hot rolling is completed at the Ar ₃ transformation point or higher, the anisotropy of the product sheet tends to increase in the case of high-purity steel, and a waste portion called an ear is formed in the container during forming, resulting in a decrease in yield. In addition, since the high-purity steel has a high Ar ₃ transformation point, it is necessary to raise the heating temperature if the finishing temperature is set to end at Ar ₃ or higher, which makes it difficult to generate AlN during heating, which is disadvantageous in aging resistance. ..

[0003]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of formability, aging and ridging that occur when a steel is highly purified, has a small anisotropy, and has a ridging resistance that suppresses the occurrence of ears as much as possible. The present invention provides a method for producing a steel sheet for extremely soft containers having excellent aging resistance.

[0004]

The inventors of the present invention have studied the components and hot rolling conditions in detail in order to achieve the above object. As a result, the C amount is limited from the viewpoint of aging resistance and the solute N amount is increased. To A
It was clarified that it is important to control by the precipitation of 1N, and it is necessary to make the hot-rolled sheet into fine particles for the ridging resistance, and this method controls the cold speed during the γ → α transformation. , It was clarified that it is effective to recrystallize the material rolled in the ferrite region. Moreover, as a method of reducing the anisotropy of the product sheet, it was found that the anisotropy of the product sheet is reduced by controlling the texture by hot rolling in the ferrite region. The present invention is constructed based on these findings, and the gist thereof is, by weight ratio, C: 0.0015% or less, N: 0.005% or less, Al: 0.3% or less, and a winding temperature CT ( ℃) and nitrogen content N (%) are included so as to satisfy the formula (1), Al (%)>-{(0.05-23 / 14N)} / 150 × CT + 0.25-4 × 23 / 14N ··· (1) Mn is added so that Mn / S becomes 5 or more, and M
Steel containing one or two or more of n, Si, Ni, Cu, Cr, and P containing 0.1% or more and 1.0% or less and the balance Fe and inevitable impurities is Ar ₃ to Ar. ₃ +
Rolling with a total reduction of 50% or more in a temperature range of 100 ° C., then cooling at an average cooling rate of 10 ° C./sec or more during γ → α transformation, and 35% or more in a temperature range of Ar ₃ or less. A method for producing a steel sheet for aging resistant ultra-soft containers with small anisotropy, which comprises rolling, winding at 750 ° C. or lower and 600 ° C. or higher, followed by pickling, cold rolling and continuous annealing.

The limiting conditions of the present invention will be described in detail below. First, the limiting conditions of the components will be described. It is known that C not only hardens steel but also deteriorates aging. Usually, in order to secure aging resistance, the C content is 0.01
% Or more to generate cementite by overaging treatment,
The method of reducing the solid solution C is adopted. With this method, when the amount of C becomes 0.01% or less, the precipitation of cementite is delayed, the amount of C fixed by overaging treatment decreases, and conversely, the amount of solid C remaining remains. The amount of molten C increases and the aging resistance deteriorates. The present inventors have clarified that by making the amount of C as low as possible, excellent aging resistance can be obtained regardless of the presence or absence of overaging treatment. The upper limit C amount is 0.0015%.

N is also an element that significantly hardens steel, and N.
When added in an amount of 005% or more, it is difficult to obtain the tempering degree of T-1 and T-2. Further, N has a great influence on the aging resistance like C, but in the case of N, AlN is formed by adding Al, and the amount of solid solution N causing aging can be controlled. Al (%)> − {(0.05−23 / 14N)} / 150 × CT + 0.25−4 × 23 / 14N ··· The conditional expression (1) limits the amount of Al required to suppress N aging. ing. Here, this amount is a function of the winding temperature because the precipitation behavior of AlN differs depending on the winding temperature. The upper limit of the amount of Al added is set to 0.3% because the cost of aluminum as an additional alloy becomes excessive.

The amount of Mn is limited to Mn / S ≧ 5 in relation to S in the amount necessary to precipitate MnS in order to prevent hot embrittlement due to inevitable S.
The lower limit of the sum of one or more of Mn, Si, Ni, Cu, Cr, and P is set to 0.1%, because the addition amount below this amount causes the grain coarsening to be remarkable and the hot-rolled sheet to have coarse grains. This is because there is a high possibility that ridging will occur. On the other hand, if the total sum of these elements exceeds 1%, the curing becomes large, and the tempers of T-1 and T-2 cannot be achieved.

Next, the limiting conditions of the hot rolling process will be described. In the temperature range of Ar _{3 to} Ar ₃ + 100 ° C., the lower limit of the total rolling reduction is set to 50%, because the rolling reduction below this is that ferrite after transformation is transformed even if the cold speed during γ → α transformation is 10 ° C./s or more. This is because the structure becomes coarse and ridging occurs on the product plate. Similarly, even if the total rolling reduction is 50% or more,
The lower limit of the average cold speed during the γ → α transformation was set to 10 ° C / s. A
The hot rolling reduction rate in the temperature range below the r ₃ transformation point is set to 35% or more because the recrystallization grains generated during cooling or winding become coarse and the ridging occurs in the product sheet at the rolling reduction below this range. This is because. Further, if the rolling reduction is less than this, the texture formed by the hot-rolled sheet is weak, it is insufficient to control the texture of the product sheet, the anisotropy cannot be reduced, and large ears occur. This is because. The mechanism by which texture control in hot rolling suppresses the occurrence of ears of the product sheet is that hot rolling below the Ar ₃ transformation point causes the hot rolled sheet to form a strong anisotropy with an inverted V-shaped γ value, and It is considered that the anisotropy is reduced by causing the V-type γ-value anisotropies generally formed by stretching and annealing to cancel each other out. Ar to control this texture
_{In order} to effectively use the rolling of ₃ transformation points or less, it is preferable that the total reduction ratio is at least 35% or more, preferably 50% or more.

The upper limit of the coiling temperature is set to 750 ° C. because the coiling temperature higher than 750 ° C. causes the hot-rolled sheet to coarsen due to grain growth and deteriorates the corrosion resistance as a steel sheet for containers. The lower limit of 600 ° C. is because recrystallization does not occur at a coiling temperature lower than this temperature, the hot-rolled sheet exhibits a processed structure, and ridging occurs in the product sheet. The pickling, cold rolling and annealing conditions are not particularly specified, but the feature of the present invention is that T- which can be produced only by conventional box annealing.
That is, the steel sheets 1 and 2 for soft containers can be manufactured by continuous annealing.

[0010]

EXAMPLES Table 2 shows the Δr value, hardness and ridging of cold-rolled steel sheets and the presence or absence of stretcher strain when the hot-rolling conditions were variously changed using the steels shown in Table 1. Here, the cold rolling rate is 90%, the annealing is continuous annealing, and the plate temperature is 730 ° C.
Then, recrystallization annealing is performed for 60 seconds, and the plate thickness is 0.3 mm. The skin pass is 1%, and the occurrence of ridging is 21
After aging treatment at 0 ° C. for 30 minutes, a bulge height of 10 mm was given in a 190 mm diameter liquid bulge test to make a visual judgment. Experiment No. within the scope of the present invention. 1, 2, 5, 9, 15
Has a low Δγ, almost no generation of ears, hardness is sufficient to satisfy the tempering degrees T-1 and T-2, and ridging and stretcher strain are not generated. On the other hand, Ar
Experiment N in which the rolling reduction of _{3 to} Ar ₃ + 100 ° C. is as small as 40% N
o. In No. 3, ridging was generated, which is considered to be caused by the coarse particles of the hot rolled sheet. 30% reduction below Ar ₃ transformation point
Experiment No. which was low. In No. 6, Δγ was large and ridging was generated. Experiment No. 1 having a high winding temperature of 785 ° C. In No. 7, ridging that was considered to be caused by the coarse particles of the hot-rolled sheet was observed. Experiment No. whose winding temperature is lower than the limiting condition of the present invention. In No. 8, not only did ridging occur because the hot-rolled sheet had a processed structure, but also Δγ was large, and solute N also remained, so stretcher strain was also observed.

Experiment No. 1 which did not satisfy the condition of Expression 1. 1
Experiment No. 0 and 11 in which the carbon amount was added in the range of the present invention or more. In No. 13, stretcher strain occurred because solid solution N or solid solution C remained. Experiment No. in which hot rolling was completed in the γ region In No. 12, the texture control by hot rolling could not be sufficiently performed, and Δγ was increased, and ears were generated. Steel D that did not satisfy the scope of the present invention because the additive elements were reduced as much as possible
Experiment No. In No. 14, ridging was generated, which is thought to be due to coarse particles in the hot-rolled sheet. On the other hand, Experiment No. using Steel F in which the additive element was added in the range of the present invention or more. In No. 16, curing is so remarkable that the tempers T-1 and T-2 cannot be satisfied.

[0012]

[Table 1]

[0013]

[Table 2]

[0014]

According to the present invention, the slab heating temperature can be lowered, T-1 and T-2 can be produced by continuous annealing, and energy saving, shortening of production days, labor productivity, etc. are improved. Further, the improvement of anisotropy can suppress the occurrence of ears as much as possible, improve the product yield, and have great industrial significance.

Claims (1)

[Claims] 1. A weight ratio of C: 0.0015% or less, N: 0.005% or less, Al: 0.3% or less, and a relation between a winding temperature CT (° C.) and a nitrogen content N (%). Al (%)> − {(0.05-23 / 14N)} / 150 × CT + 0.25−4 × 23 / 14N ··· (1) Mn / S is 5 or more. Mn is added so that
Steel containing one or two or more of n, Si, Ni, Cu, Cr, and P containing 0.1% or more and 1.0% or less and the balance Fe and inevitable impurities is Ar ₃ to Ar. ₃ +
Rolling with a total reduction of 50% or more in a temperature range of 100 ° C., then cooling at an average cooling rate of 10 ° C./sec or more during γ → α transformation, and 35% or more in a temperature range of Ar ₃ or less. A method for producing a steel sheet for aging extremely soft containers having small anisotropy, which comprises rolling, winding at 750 ° C or lower and 600 ° C or higher, and then pickling, cold rolling, and continuous annealing.