JPH073334A - Production of steel sheet for low earing vessel - Google Patents

Abstract

PURPOSE:To eliminate the causing of stretcher strains by subjecting dead soft steel having a specified compsn. to hot rolling, specifying the cooling rate, executing coiling, specifying the relationship between the sheet thickness after cold rolling and the sheet thickness of the hot rolled sheet and executing cold rolling. CONSTITUTION:Steel constituted of, by weight, <=0.003% C, <=0.2% Si, <=0.6% Mn, 0.01 to 0.1% Al and <=0.005% N, and the balance Fe is subjected to hot rolling at >=840 deg.C. The average cooling rate till coiling is regulated to 50 deg.C/sec, and it is coiled at deg.4O0 deg.C. After pickling, cold rolling is executed at 0.5 to 50% cold rolling ratio after recrystallization annealing so as to establish (th-tf)/ th<0.96 between the sheet thickness (th) of the hot rolled sheet and the final sheet thickness (tf) after the cold rolling, recrystallization annealing and subsequent cold rolling to regulate (tf) into 0.12 to 0.22mm. In this way, the plating original sheet for an extremely thin vessel small in earing can be obtd.

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 plating base plate for an ultrathin container, which is excellent in earring resistance and does not cause stretcher strain.

[0002]

2. Description of the Related Art The market demands for an extremely thin original plate for a container from the viewpoint of weight saving and resource saving. Corresponding to this,
Material suppliers are making efforts to achieve ultra-thinness by increasing the cold rolling rate in the conventional hot rolling-cold rolling-annealing-temper rolling. However, in this case, since the plate thickness is already extremely thin after cold rolling, it is difficult to pass the plate when annealing is carried out by continuous annealing, the shape deteriorates, and in some cases plate breakage occurs, which is a major problem not only in quality but also in operation. May become. As a technique for avoiding this problem, the aim is to reduce the sheet thickness of ultra-low C steel after cold rolling to an extremely thin thickness, and after annealing, perform cold rolling at a larger reduction rate than conventional temper rolling. Japanese Patent Publication No. 1-52451 discloses a technique for reducing the plate thickness.

However, the steel sheet produced in this manner has a large anisotropy, and in a two-piece can produced by DI (drawing and ironing) processing, after the DI processing, the opening has a height of the can body called earring. Non-uniformity occurs remarkably (Earring rate is an index that quantitatively expresses earrings. This is the value obtained by subtracting the minimum value from the maximum value of the barrel height and dividing by the maximum value, and then multiplying by 100. However, if the earrings are large, trimming is performed to make the can body heights uniform, which not only lowers the yield but also increases the cost because one process is added. The problem with this earring is not only when the cold rolling rate after annealing is large,
It also tends to become apparent when the cold rolling reduction before annealing is large. As a countermeasure against this, it is conceivable to reduce the cold rolling reduction by reducing the thickness of the hot rolled sheet. However, thinning of the hot-rolled sheet causes a decrease in finishing temperature and an increase in rolling load, which not only causes a problem in quality and stability of the threaded sheet but also causes an increase in pickling cost due to an increase in surface area.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems of the prior art and to provide a method for manufacturing a steel sheet for ultra-thin containers with small earrings by an economical method.

[0005]

Means for Solving the Problems The present inventor has studied in detail the influence of the manufacturing conditions on the earrings of a steel sheet for ultra-thin containers, and has been able to heat ultra-low carbon steel without making the hot-rolled sheet extremely thin. After rolling, it was clarified that it can be significantly reduced by winding at ultra-low temperature. It was also clarified that the cold speed after hot rolling had a great influence on the formation of earrings. The present invention is based on these findings and has the following structures. That is, C: 0.003% or less by weight,
Si: 0.2% or less, Mn: 0.6% or less,
Al: 0.005% or more, 0.1% or less, N: 0.0
05% or less, and in some cases Ti: 0.05%
Below, Nb: 0.05% or less, Zr: 0.05%
Hereinafter, B: steel containing at least one of 0.005% or less and the balance of Fe and inevitable impurities is hot-rolled at a temperature of 840 ° C. or higher, preferably after finishing rolling, the average of up to 800 ° C. The cold speed is 30 ℃ / sec or less, and the average cold speed after rolling after rolling is 50 ℃ / sec.
After winding and pickling at a temperature of 00 ° C. or less, between the thickness t h of the hot rolled sheet and the final sheet thickness t f after cold rolling, recrystallization annealing and subsequent cold rolling (th −t f) / Th <0.96 is satisfied, and the cold rolling rate after recrystallization annealing is 0.5% or more, 50
% Or less and tf of 0.22 mm or less and 0.12 mm or more, which is a method for producing a steel sheet for ultra-thin containers excellent in low earring property without causing stretcher strain.

Next, the limiting conditions of the present invention will be described. First,
The conditions for limiting the components will be described. There are several reasons why the amount of C is set to 0.003% or less. First, after rolling,
By lowering the average cold speed until winding to 50 ° C./sec and winding at a temperature of 400 ° C. or lower, the lower limit of the amount of C added must be 0.003% in order to significantly reduce the earring. It is also one of the reasons that stretcher strain is generated when C is added further. If N remains in the steel in the form of a solid solution, it will cause stretcher strain to occur, so normally it is in the form of precipitates such as AlN and TiN, but if the amount of precipitates increases, the workability deteriorates. , N were limited to 0.005% or less.

The amount of Al is necessary to fix N as aluminum nitride, and is required to be at least 0.01%. However, when a nitride-forming element such as Ti, Nb, Zr, or B is added in addition, 0.005% or more may be added with a focus on sufficiently performing Al deoxidation. Further, addition of a large amount not only increases the cost but also deteriorates workability, so the upper limit of the addition amount is 0.1%. The addition amounts of Si and Mn are limited to Si: 0.2% or less and Mn: 0.6% or less. If these alloys are further added, workability deteriorates and corrosion resistance is impaired. Also, Ti, Nb,
The addition of Zr and B forms carbonitrides and improves the workability by eliminating the solid solution C and N. However, addition of a large amount not only increases the cost but also deteriorates the workability. The upper limit of each addition amount is Ti: 0.05% or less, Nb:
0.05% or less, Zr: 0.05% or less, B: 0.00
It was set to 5% or less.

Next, the limitation of manufacturing conditions will be described. The hot rolling finishing temperature is set to 840 ° C. or higher. With the composition of the steel of the present invention, if finish rolling is performed at a temperature lower than this, a part or all of the composition becomes a ferrite structure during finish rolling, and the former tends to cause variations in properties. This is because the earring rate increases in the latter case. The reason why the winding temperature is 400 ° C. or lower is that the earring can be reduced when the winding temperature satisfies this limiting condition as shown in FIGS. The reason for this is not clear, but by lowering the coiling temperature, the amount of solute C and N increases, or the precipitates that form become finer. Therefore, these are aggregates formed during cold rolling and annealing. It is thought to have affected the organization and consequently reduced the earrings.

On the other hand, the reason why the cooling rate from finish rolling to winding at 400 ° C. or lower is 50 ° C./sec or more on average is that the earring does not become remarkably small when the cooling rate is lower than this. It is presumed that this is because, as in the above case, when the average cooling rate is 50 ° C./sec or less, the amount of solid-soluted C and N decreases, and the produced precipitate does not become sufficiently fine. On the other hand, after rolling,
The upper limit of the average cooling rate up to 800 ° C. of 30 ° C./sec or less is limited, because the earring rate is further reduced by satisfying this limiting condition. It is considered that this is because the grain size of ferrite generated due to the low cooling rate during transformation was coarsened, which contributed to the reduction of the earring. However, after rolling, the average cold speed up to 800 ° C is 3
If the rate is 0 ° C / sec or less, the earring rate will not decrease so much, and the average cooling speed after rolling after rolling is 50 ° C / sec.
Only when the conditions of winding at a temperature of 400 ° C. or less are satisfied at the same time, a remarkable reduction in the earring rate can be achieved.

In the relationship between the thickness t h of the hot-rolled sheet and the final sheet thickness t f, the limiting condition is (th −t f) / th <0.96, as shown in FIG. This is because the steel of the present invention exhibits excellent earring resistance as compared with the comparative steel. Here, as shown in FIG. 2, even if the sheet thickness reduction is achieved only by the cold rolling before the recrystallization annealing, the cold rolling is performed in the recrystallization annealing, and the combination of the cold rolling before the recrystallization annealing is performed. Even if it achieves, it shows almost the same effect on the earring resistance.

The cold rolling rate after recrystallization annealing is 0.5% or more, 5
The reason why it is limited to 0% or less is that the tempering effect cannot be sufficiently obtained at a cold rolling rate of 0.5% or less. The cold rolling rate is 50
This is because if it exceeds%, the probability of forming defects such as bottle wrinkles, neck wrinkles, flange cracks, tear-offs during DI processing increases. The reason why the final thickness tf is limited to 0.22 mm or less and 0.12 mm or more is that the final thickness tf is 0.
This is because if the thickness is 22 mm or more, the original goals of weight reduction and resource saving cannot be effectively achieved. Also, the final plate thickness tf
Is less than 0.12 mm, the rigidity of the bottom of the can becomes too small and the pressure inside the can remarkably changes the shape.

As described above, according to the basic structure of the present invention, the cold rolling ratio showing the high earring ratio is conventionally obtained by winding the ultra low carbon steel at an extremely low temperature (the reduction ratio of the cold rolling before and after the recrystallization annealing). It is said that the earring rate can be reduced within the range of (1) and the ultra-thin steel sheet for containers can be manufactured, which is based on an unprecedented idea.

[0013]

EXAMPLES Table 1 shows the chemical composition of the steel of the present invention and the comparative steel.
Table 2 shows the earring rate, the presence or absence of bottom creases, the presence or absence of neck creases, the proof pressure strength, and the presence or absence of stretcher strain when the steel sheets manufactured under various manufacturing conditions are DI processed using the materials of Table 1. The results of examination are shown below. The presence or absence of bottom wrinkles, neck wrinkles, and stretcher strain was judged by visual observation. The compressive strength is defined as the pressure when the can bottom is inverted by the internal pressure in the shape of the can bottom shown in FIG.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

[Table 3]

[0017]

[Table 4]

[0018]

[Table 5]

Experiment Nos. 1, 2, 4, 5, which are steels of the present invention
8, 9, 11, 14, 16, 17, 18, 21, 22, 22
Nos. 23, 24, and 25 had a low earring rate, satisfied the pressure resistance, and did not generate bottom wrinkles, neck wrinkles, stretcher strains, etc., and showed excellent canned formation. In Experiment No. 3 in which the hot rolling finishing temperature was below the range of the present invention, the earring rate was high probably because the texture of the hot rolled sheet was different. Experiment numbers 6 and 10 in which the winding temperature exceeded the range of the present invention
Both showed high earring rates. Further, Experiment No. 7 in which the average cold speed from finish rolling to winding was below the range of the present invention also showed a high earring rate. (Th-tf) / t
Experiment number 12, in which the h ratio exceeded the range of the present invention, also showed a high earring rate. In Experiment No. 13 in which 60% cold rolling was performed after recrystallization annealing, wrinkles were observed during can forming, probably because work hardening was large. Also, the final plate thickness is 0.11 mm
In Experiment No. 15 thinner than the range of the present invention, in addition to the occurrence of bottom wrinkles, the pressure resistance did not reach the acceptable level.
Experiment No. 1 in which C and N were added in excess of the range of the present invention
Stretcher strain occurred on 9, 20, and 26. In particular, wrinkles were also observed in Experiment No. 26, in which the amount of C was large.

[0020]

INDUSTRIAL APPLICABILITY As described above, the present invention provides a new technique capable of reducing earrings, which has been a problem in the production of steel sheets for ultrathin containers, and has a great industrial significance.

[Brief description of drawings]

FIG. 1 shows the effect of winding temperature on the earring rate.

FIG. 2 shows the relationship between the ratio of (hot-rolled sheet thickness-final sheet thickness) and hot-rolled sheet thickness that affect the earring rate and the winding temperature as parameters.

FIG. 3 shows the shape of the bottom of a can whose pressure resistance is measured.

Claims (3)

[Claims] 1. By weight ratio, C: 0.003% or less, Si: 0.2% or less, Mn: 0.6% or less, Al: 0.01% or more, 0.1% or less, N: 0. Steel containing 005% or less and the balance of Fe and unavoidable impurities is hot-rolled at a temperature of 840 ° C. or higher, and the average cold speed until rolling after rolling is 50 ° C./sec.
After winding and pickling at a temperature of 00 ° C. or less, between the thickness t h of the hot rolled sheet and the final sheet thickness t f after cold rolling, recrystallization annealing and subsequent cold rolling (th −t f) / Th <0.96 is satisfied, and the cold rolling rate after recrystallization annealing is 0.5% or more, 50
% Or less, and tf is 0.22 mm or less and 0.12 mm or more, a method for producing a steel plate for a low earring container free from stretcher strain. 2. By weight ratio, C: 0.003% or less, Si: 0.2% or less, Mn: 0.6% or less, Al: 0.005% or more, 0.1% or less, N: 0. 005% or less, further Ti: 0.05% or less, Nb: 0.05% or less, Zr: 0.05% or less, B: 0.005% or less, at least one kind is included,
Steel with balance of Fe and inevitable impurities at 840 ° C
After hot rolling at the above temperature, the average cold speed after rolling to winding is 50 ° C / sec, winding at a temperature of 400 ° C or less, pickling, hot rolled sheet thickness tf and cold rolling , Recrystallization annealing, and then cold rolling, during the final plate thickness tf (th-tf
) / Th <0.96, the cold rolling rate after recrystallization annealing is 0.5% or more and 50% or less, and tf is 0.22.
A method for producing a steel plate for a low earring container, in which stretcher strain does not occur, wherein the steel sheet has a thickness of 0.1 mm or less and 0.12 mm or more. 3. The average cooling rate after finishing hot rolling to 800 ° C. is 30 ° C./sec or less.
Alternatively, the method for producing a steel plate for a low earring container, according to 2, wherein the stretcher strain does not occur.