KR880000286B1 - Method of producting black plate - Google Patents

Abstract

A method for producing soft black plate comprises steps to; (i) eat slab that is obtd. by addn. of Cr(Cr/C=1.5-2) to steel having c:0.03- 0.06%, Mn:below 0.40%, Al:below 0.02%, Si: below 0.06%, P and S:below 0.015% up to 1250 deg.C; (ii) hot-rolling at the temp. (880 deg.C) and to wind at 650-720 deg.C; (iii) coldrolling by pressure fall-off rate of 80-90% and (iv) recrystallize -anneal in the continuous annealing furnace (for hand black plate) at 720-740 deg.C.

Description

Method for producing soft stone disc

1 is a graph showing the ferrite grain size number change according to the C, Mn, Si content.

2 is a graph showing the change in ferrite grain size according to the coiling temperature and the annealing temperature.

The present invention relates to a method for producing a soft stone fine plate of the fineness T-3 using a continuous annealing furnace for the production of hard stone discs with a fineness T-4 or more of the raw material produced by continuous casting of the Si attenuated steel. Generally, tin plate plated with tin on black plate (BP) is widely used as a container for food and beverage because it has excellent corrosion resistance and harmless to human body. Therefore, the factors that determine the quality characteristics of BP include processability and corrosion resistance, and various grades of products are made according to their use. Dividing stone discs according to the degree of control ranges from grade T-1 for deef drawing to grade T-6 for beer can lids requiring strength. In order to manufacture a soft stone disc of below T-3 grade, it is necessary to grow crystal grains and lower the dissolved carbon content in the crystal grains.In the continuous annealing furnace for hard stone discs, the cooling rate after cracking is not fast enough to precipitate solid carbon. As a result, it is difficult to manufacture a disc of soft stone having a T-3 of roughness using general low carbon steel as a material. On the other hand, in the case of box annealing, a sufficient cooling carbon is precipitated during cooling, so that a soft stone disc can be manufactured. . However, the box annealing method is an annealing method in which a coil is loaded. Since the heat capacity of the loaded coil is large, an annealing time of about 10 hours is required to reach the predetermined annealing temperature. In addition, the cooling after cracking is extremely slow, and it takes more than 2 days to cool the temperature from the cracking temperature around 600 ℃ to room temperature, which is inefficient in terms of productivity.

Therefore, in recent years, by using ultra-low carbon steel as a material to reduce the dissolved carbon to a harmless range, the method of preventing hardness increase by solid carbon even in the state of quenching after annealing and in the conventional continuous annealing furnace for hard stone disc A method of installing an overaging zone to sufficiently precipitate solid solution carbon during cooling has been put into practical use. However, in order to manufacture ultra-low carbon steel, it is required to go through vacuum degassing process of RH-OB after tapping, which increases the manufacturing cost. Also, it is a general low-carbon steel. In manufacturing, a retrofit to the plant was required, including the installation of a aging band during the existing continuous annealing process.

Therefore, the present invention is to provide a method that can solve the conventional problems as described above, it is possible to stably produce a soft stone degree of fineness T-3 disc of general low carbon steel material using a conventional continuous annealing process. . In the present invention, Cr / C = 1.5-2 Cr in a weakly oxidized steel having a composition of C: 0.03-0.06%, Mn: 0.40% or less, Al: 0.02% or less, Si: 0.05% or less, P, S: 0.015% or less The slab prepared by the addition of the above was heated to more than 1250 ℃, hot rolled at the finishing rolling temperature of 880 ℃ and wound in the range of 650-720 ℃, cold rolled to 80-90% reduction rate and then hard stone disc It characterized in that the recrystallized annealing at a high temperature of 720-740 ℃ heating temperature in a continuous annealing furnace.

Hereinafter, the present invention will be described in detail.

Figure 1 shows the measurement of the size of the ferrite grains after manufacturing the stone disk under the conditions of Table 1, the test specimen AD, EH and GI in Table 1 shows the effect of C, Mn, Si on the grain size, respectively It is for measuring key.

The reason for limiting the carbon content to 0.03-0.05% in the present invention is as follows.

That is, C: 0.03% is a lower limit that can be obtained in a normal deodorizing converter. If the carbon content exceeds 0.05%, the grain size becomes finer upon recrystallization annealing and the hardness increases. According to FIG. 1, it can be seen that as the amount of carbon increases, the grain size of ferrite increases rapidly at 0.05% or more.

In the case of Mn, the grain size change of ferrite is small up to 0.40%, but it is rapidly increasing above that. Therefore, it is not preferable that the content of Mn exceeds 0.40%.

In the case of Si, the grain size number of the ferrite decreases significantly from 0.05% or more. However, when the content of Si exceeds 0.06% or more, the hardness exceeds the target due to solid solution strengthening. Therefore, Si is preferably 0.06% or less.

Al uses 0.02% for carbonation adjustment.

On the other hand, in order to soften the material of the stone master disc, it is preferable to precipitate the carbon dissolved in the ferrite grains as carbide to reduce the high capacity. In general, in the annealing method, the cooling rate is very slow, and the carbon employed in ferrite precipitates sufficiently as carbide during cooling, but in the continuous annealing process with high cooling speed, the solid solution carbon is not sufficiently precipitated, causing a hardness increase in solid solution strengthening. do.

Therefore, the present invention is to add Cr in the range of Cr / C = 1.5-2 to sufficiently control the solid solution carbon during continuous annealing, in the present invention, Cr is dissolved in cementite during hot rolling This prevents the decomposition of cementite during annealing.

Therefore, the present invention is to add the amount of chromium added to have an effect of suppressing the increase in the dissolved carbon content during the annealing process, the addition amount is in the weight ratio to the carbon content in the range of 1.5 to 2.0 hardness value in the range of fineness T-3 Will be.

2 shows ferrite grain size numbers according to the hot-rolled coiling temperature of annealing temperature of sample steel having C: 0.04%, Si: 0.05%, Mn: 0.43%, Cr: 0.06%, P and S: 0.02%.

According to FIG. 2, it can be seen that the ferrite grain size decreases as the hot rolled coil temperature increases, reaching the lowest annealing from the 650 ° C subgroup. In addition, the number of ferrite grain size decreases with increasing the annealing temperature.

On the other hand, when the coiling temperature is increased, carbide coarsening occurs at the ferrite grain boundary of the hot rolled tissue. Coarse carbides are not easily dissolved in the hot annealing process after cold rolling, thereby reducing the dissolved carbon in the ferrite and growing grains. It works. However, the increase in the coiling temperature during hot rolling increases the amount of scale produced on the coil surface, which deteriorates pickling, so the upper limit of the coiling temperature is limited to 720 ° C in normal operation.

Next, the annealing condition will be described.

Coarse Cr carbide formed by high temperature winding is a strong carbide, so it does not dissolve easily under annealing conditions of annealing temperature of 720-750 ℃ and annealing time of 40-60 seconds after cold rolling, so ferrite grains grow without causing A ₁ transformation. .

However, at temperatures above 750 ° C., the strength of the steel sheet decreases, thereby increasing the risk of heat buckles. Therefore, the upper limit of the annealing temperature is 750 ° C.

Example 1

A steel sheet containing 0.04% carbon, 0.05% manganese, and 0.34 traces of manganese was made of slab, and hot-rolled sheets were manufactured by changing the hot finish rolling temperature and winding temperature after cracking at 1250 ℃ for 2 hours. The cold rolled sheet was fabricated to investigate the characteristics of the product according to the continuous annealing temperature. At this time, the hardness measurement was performed 30 times each under the rockwell hardness load of 30kg, and the tensile test was carried out five times with a standard test piece having a gauge length of 50mm.

Example 2

Carbon: 0.05%, silicon: 0.06%, manganese: 0.26%, chromium: 0.08%, and other steels containing a small amount of impurities of P and S were tested in the same manner as in Example 1 to obtain the characteristics shown in the following table.

As can be seen from the above results, it can be seen that the hardness values of the test specimens are 54 or less, satisfactorily satisfying the hardness range 57 ± 3 of the soft stone master plate having a roughness T-3, even when the hardness increase is roughly about 3. .

Claims (1)

Cr / C = 1.5-2 Cr is added to the attenuated steel having a composition of C: 0.03-0.06%, Mn: 0.40% or less, Al: 0.02% or less, Si: 0.06% or less, P and S: 0.015% or less After heating the produced slab to more than 1250 ℃, hot rolling at the finishing rolling temperature of 880 ℃ and wound in the range of 650-720 ℃, cold-rolled to a reduction ratio of 80-90% and then heated in a hard stone master disc continuous annealing furnace A method for producing a soft stone master disc, characterized in that the recrystallization annealing at a high temperature of 720-740 ℃.

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