JP2000045030A - Manufacture of cold-rolled sheet of low carbon steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a cold-rolled sheet of low carbon steel excellent in deep drawability by drum caster casting. SOLUTION: The cold-rolled sheet of a low carbon steel can be manufactured by applying a drum caster casting to a low carbon steel containing <=0.1 wt.% C, subjecting the resultant ingot to hot-rolling at a draft of <=50% and to cold- rolling at a draft of 40 to 80%, and then applying annealing treatment at a temp. of 800 to 1,000 deg.C. At this time, heat treatment at 1000 to 1200 deg.C is carried out before hot rolling. Further, heat treatment is carried out at a temp. of 600 to 800 deg.C after hot rolling, and cooling is performed down to a temperature not higher than the α-transformation point after drum caster casting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a cold-rolled low carbon steel sheet, and more particularly to a method for producing a cold-rolled low carbon steel sheet having excellent deep drawing characteristics by a process including drum caster casting.

[0002]

2. Description of the Related Art Conventionally, slab continuous casting equipment has a thickness of 50 mm.
The above-mentioned ingot was manufactured and rolled by hot rolling and cold rolling equipment to obtain a cold-rolled low carbon steel sheet having a thickness of about 1 mm. In order to roll an ingot obtained by continuous slab casting, a large-scale rolling facility is required, and the use of these facilities requires a large amount of energy.

[0003] As a method of solving the problem caused by continuous slab casting, there is drum caster casting. In the drum caster casting, a thin slab having a thickness of 1 to 10 mm can be cast by pouring molten steel between a pair of rotating water-cooled drums. For this reason, a low-carbon steel cold-rolled sheet as a final product can be obtained by a slight rolling, and the rolling process can be simplified and the production energy can be reduced as compared with continuous slab casting.

[0004]

However, cold rolled low carbon steel sheets rolled from thin slabs obtained by drum caster casting have a greater depth than cold rolled low carbon steel sheets manufactured by a process including continuous slab casting. There is a problem that the aperture characteristic is inferior.

Accordingly, an object of the present invention is to provide a method for manufacturing a cold-rolled low carbon steel sheet having excellent deep drawing characteristics by drum caster casting.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, the deep drawing characteristics of a low-carbon steel cold-rolled sheet obtained by rolling after casting of a drum caster have been improved by the continuous drawing of slab. The inferiority to the low-carbon steel cold-rolled sheet produced by rolling after casting is that the crystal texture of the low-carbon steel cold-rolled sheet is such that the {111} planes of the crystal grains in the sheet have the normal direction of the sheet. It was found that this was because the ratio of pointing was low. That is, the low-carbon steel cold-rolled obtained by rolling after continuous slab casting has excellent deep drawing characteristics in which the ratio of the {111} plane of the crystal grains is oriented in the direction of the normal to the sheet material, and excellent deep drawing characteristics can be obtained. In the low-carbon steel cold-rolled sheet obtained by casting and rolling after casting, crystal grains of
The deep drawing characteristics were inferior because the ratio of the 1 ° plane oriented in the normal direction of the plate material was low.

The present inventors have studied the casting conditions, the rolling reduction during rolling, the rolling temperature, the annealing conditions, and the like based on the above findings, and by controlling these conditions, the {111} plane of the crystal grains was obtained. It can be found that the ratio of directing the surface normal direction of the plate material can be increased.

[0008] That is, the present invention relates to the method of
The following low carbon steel containing C is cast on a drum caster,
The obtained ingot is subjected to hot rolling at a rolling reduction of 50% or less, and a rolling reduction of 4%.
0-80% cold rolling, then 800-1000
A method for producing a low-carbon steel cold-rolled sheet, characterized by performing an annealing treatment at ℃. Further, in the present invention, heat treatment at 1000 to 1200 ° C. before hot rolling and 600 to 1200 ° C. after hot rolling.
Heat treatment at 800 ° C. is desirable from the viewpoint of improving the deep drawing characteristics. Further, in the present invention, the hot rolling may be in-line rolling in which the temperature is maintained after casting, but may be cooled to a γ → α transformation point or less after the drum caster casting.

According to the method for manufacturing a cold-rolled low carbon steel sheet according to the present invention, the process by drum caster casting can be simplified and energy consumption can be reduced, and the texture can be controlled in the process after drum caster casting. In addition, the ratio of the {111} plane of the crystal grains of the low-carbon steel cold-rolled sheet oriented in the surface normal direction of the sheet material is increased, and excellent deep drawing characteristics can be obtained.

[0010] In the present invention, hot rolling and cold rolling have a role of introducing strain into the structure and then forming a new texture by recrystallization. In hot rolling, recrystallization occurs during and after rolling at a high temperature. In cold rolling, recrystallization occurs during the subsequent annealing treatment.

The plane orientation of the recrystallized grains is the texture before rolling,
It is affected by the distribution of precipitates in the crystal grains and the solid solubility of carbon during recrystallization together with the work structure after rolling. Therefore, by setting the rolling reduction at the time of hot rolling to 50% or less and the rolling reduction at the time of cold rolling to 40 to 80%, the work structure before recrystallization is controlled, and excellent deep drawing characteristics can be obtained.

The reduction rate of hot rolling is set to 50% or less when a cold rolled steel sheet of about 1 mm is formed from a thin slab in order to obtain a sufficient reduction rate during cold rolling. This is because the rate must be reduced. In addition, hot rolling is performed by
It is desirable to carry out in the range of 000 to 1200 ° C. 10
If the temperature is lower than 00 ° C., recrystallization after hot rolling does not occur, and a decrease in elongation of the sheet material due to the remaining work structure is expected. If the temperature exceeds 1200 ° C., recrystallization grains become coarse. This is because a decrease in the strength of the plate material is expected.
The reduction ratio of the cold rolling is set to 40 to 80% for the following reason. That is, the plane orientation of the recrystallized grains generated by annealing depends on the rolling reduction at the time of cold rolling, and the {111} plane parallel to the plate surface preferable for deep drawing characteristics is formed from a cold-rolled structure having a rolling reduction of about 70%. This is because, at the rolling reduction greatly deviated from 70%, the {111} plane is not parallel to the plate surface, and γ decreases.

[0013] close to the _3-point A after cold rolling 800-100
By performing the annealing at 0 ° C., the recrystallization texture is improved, and the deep drawing characteristics are improved. If the annealing temperature is lower than 800 ° C., this effect is insufficient, and if it exceeds 1000 ° C., the crystal grains are coarsened during annealing and the strength of the sheet material is reduced. Desirable annealing temperature is 850-950 ° C.
The annealing time is desirably in the range of 1 min to 30 min. If less than 1 min, the effect is not sufficient.
This is because, if the ratio exceeds, the crystal grains become coarse and the strength is reduced.

In the present invention, MnS, A, which promotes the growth of {111} planes by heat treatment before and after hot rolling.
Precipitation of 1N, coarsening of intragranular carbide that inhibits the growth of the {111} plane, and lowering the solid solubility of carbon are effective for obtaining good deep drawing characteristics. MnS is precipitated by heat treatment at 1000 to 1200 ° C. before hot rolling, and AlN is precipitated by heat treatment at 600 to 800 ° C. after hot rolling.
Desirable heat treatment temperature before hot rolling is 1050 to 1150
° C, a desirable heat treatment temperature after hot rolling is 650 to 750.
° C.

If the heat treatment time is long, the strength is expected to decrease due to the coarsening of the crystal grains. Therefore, the heat treatment before hot rolling is 10 minutes or less, and the heat treatment after hot rolling is 6 minutes.
It is desirable to set the time to 0 minutes or less. A more desirable heat treatment time is 5 minutes or less for heat treatment before hot rolling, and 30 minutes for heat treatment after hot rolling.

[0016] In hot rolling, even in-line rolling in which the temperature is maintained after casting, γ → α
Reheating after cooling to below the transformation point may be performed, but by reheating after cooling, α generated during cooling and reheating
The diameter and orientation of the crystal grains are made uniform by the phase transformation of γ and γ, so that the deep drawing characteristics are further improved.

The present invention is used for the production of cold rolled low carbon steel sheets containing 0.1% by weight or less of C by weight. Here, C is set to 0.1% or less because the lower the C concentration, the higher the deep drawing characteristics. Note that other elements, namely, M
Elements such as n, Si, P, S, Al, and N are not particularly limited.

[0018]

Next, the present invention will be described based on an embodiment. Drum caster was cast from low carbon steel having the composition shown in Table 1 to obtain a 2.0 mm thick drum caster slab.
Drum caster casting was performed at a casting speed of 40 m / min and a casting temperature of 1585 ° C. After that, under the conditions shown in FIG. 1 to 10 low-carbon steel cold-rolled sheets were obtained. FIG.
Next, a manufacturing method according to the present invention is illustrated. In FIG. 1, hot rolling is hot rolling and cold rolling is cold rolling. Table 2 shows the presence or absence of each step in FIG. 1, the conditions, the thickness of the obtained low-carbon steel cold-rolled sheet, and the γ value as an evaluation result of the deep drawing characteristics.

In FIG. 1 and Table 2, in the case of No. For room temperature 3, room temperature (2
(0 ° C.) and then reheated to 1100 ° C. Also,
Heat treatment before hot rolling is 1100 ℃ × 5mi
After the hot rolling at 1100 ° C., the heat treatment as the heat treatment after the hot rolling was performed at 700 ° C. × 30 min. Then, it cold-rolled and performed 1 minute annealing.

As a conventional example, a low carbon steel having a composition shown in Table 1 was continuously cast at 1100 ° C. and a reduction rate of 90% was obtained.
Hot rolling, cold rolling at a reduction of 70%,
An annealing treatment of × 1 min was performed to obtain a cold-rolled low-carbon steel sheet having a thickness of 0.8 mm (No. 11).

The obtained No. The γ value, which is an index of the deep drawing characteristics, of the low-rolled steel sheets 1 to 11 was determined. Table 2 shows the results. Note that γ is 0 ° with respect to the rolling direction,
The tensile test specimens at angles of 90 ° and 90 ° were pulled 15%, and the sheet width and the evaluation distance before and after the tension were measured.

The comparative example No. 1 and N which is an example of the present invention
o. 5 is 40% reduction after casting the drum caster
Hot rolling and cold rolling with a rolling reduction of 70%,
The annealing temperature after that was different, and No. 5 has a high γ value of 1.19, whereas 720 ° C.
No. which was annealed 1 has a low γ value of 0.91.
No. No. 2 is No. Heat treatment was performed before and after the hot rolling of No. 5, but the γ value was further improved to 1.28 by performing the heat treatment. No. No. 3 is No. 2
After the casting of the drum caster, cooling and reheating were performed, and a more favorable γ value of 1.32 was obtained. N
o. No. 4 is No. In this case, the reduction ratio during hot rolling was changed, and it can be seen that the higher the reduction ratio, the higher the γ value.

In the case of No. 3 in which the rolling reduction during cold rolling was changed.
Comparing 2, 6, and 7, it can be seen that the γ value is the highest at a rolling reduction of 70%, and the γ value decreases when it exceeds 80%. No. 3 in which the annealing temperature was changed. Comparing 2,8,9,10, the γ value becomes highest at the annealing temperature of 900 ° C, and 800 ° C.
It can be seen that if it is less than this, a sufficient γ value cannot be obtained. Also,
No. by slab continuous casting In No. 11, the γ value was 1.22, and it was confirmed that the same deep drawing characteristics as in the continuous slab casting were obtained by drum casting according to the present invention.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

According to the present invention, a low-carbon steel cold-rolled sheet having the same deep drawing characteristics as slab casting can be obtained even by drum caster casting, which can simplify the process and reduce energy consumption.

[Brief description of the drawings]

FIG. 1 is a diagram showing a manufacturing process of a low-carbon steel cold-rolled sheet of the present invention.

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Claims (4)

[Claims] 1. A low-carbon steel containing 0.1% or less of C by weight is cast on a drum caster, and the obtained ingot is hot-rolled at a reduction of 50% or less, and a reduction of 40 to 80%. A method of producing a cold-rolled low-carbon steel sheet, comprising: performing cold rolling of the sheet, and thereafter performing an annealing treatment at 800 to 1000 ° C. 2. The method for producing a cold-rolled low carbon steel sheet according to claim 1, wherein a heat treatment at 1000 to 1200 ° C. is performed before hot rolling. 3. The method for producing a cold-rolled low carbon steel sheet according to claim 1, wherein a heat treatment at 600 to 800 ° C. is performed after the hot rolling. 4. The method for producing a low-carbon steel cold-rolled sheet according to claim 1, wherein after the drum caster is cast, it is cooled to an α transformation point or lower.