JP3244956B2 - Method for producing ultra-thin container steel sheet with excellent can formability - Google Patents

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 an ultra-thin steel sheet having excellent ductility, particularly excellent local ductility, used for containers represented by food cans and beverage cans.

[0002]

2. Description of the Related Art In the manufacture of beverage cans, food cans, and the like, the joining of a can lid or a can bottom to a body is usually performed by crimping, so that the open end of the body faces the outside of the diameter of the can body. It undergoes a process called flange forming to be stretched. In the case of this flange forming, it is required that cracks which cause leakage of contents to the flange portion and defects generally called flange cracks hardly occur. This flange formability is regarded as extremely important in the can manufacturing process, and the rate of occurrence of flange cracks is currently suppressed to a level of several tens ppm in cans which are usually manufactured. It has been known from research and development so far that the flange formability is closely related to the ductility of a steel sheet, and that a steel sheet having excellent ductility, particularly local ductility, exhibits good flange formability.

On the other hand, the steel sheet for containers is becoming thinner from the viewpoint of cost reduction, and the ductility of the steel sheet is deteriorated. Therefore, a steel sheet which is extremely thin and has good flange formability is required. In addition, in the manufacturing process of a steel sheet, the reduction ratio of the cold rolling is increased or the thickness of the hot rolled sheet is reduced in accordance with the reduction in thickness.
However, an increase in the cold rolling ratio causes an increase in the in-plane anisotropy of the Rankford value of the steel sheet, and the yield of the steel sheet decreases due to a fluctuation in the edge height of a cup called an earring in a two-piece can manufactured by drawing. . Also, the local ductility, which is closely related to the Rankford value, is greatly degraded in some directions. Further, a decrease in the thickness of the hot-rolled sheet becomes a factor that hinders productivity in hot-rolling. Further, ultra-thin materials tend to break the steel plate, called a heat buckle, during continuous annealing, and therefore have extremely poor threading properties. In particular, it is difficult to thread steel sheets at high temperatures, which lowers the strength of the steel sheets. Therefore, if the annealing temperature is lowered, recrystallization becomes insufficient and ductility is extremely deteriorated.

In order to solve these problems, a so-called DR method (double reduction method) is used, in which the thickness of the sheet is made thicker than the final product during annealing, and the sheet thickness is obtained by re-cold rolling after annealing. JP-A-3-257123, JP-A-2-1-1
18026 and the like. However, since ductility deterioration of the steel sheet due to re-cold rolling is inevitable, it is disadvantageous in terms of flange formability, and it is impossible to produce a soft material due to work hardening. On the other hand, JP-A-63-89625 and JP-A-2-197 describe that the DR method is not essential.
523 and JP-A-3-236446 have been proposed. However, in these methods, no consideration is given to the threading property (heat buckle resistance) of the continuous annealing line of an extremely thin material, and productivity impairment in actual production cannot be avoided.

[0005]

SUMMARY OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and it is preferable to perform annealing at a relatively low temperature at which the productivity can be prevented from decreasing during the continuous annealing step. An object of the present invention is to provide a method for producing a steel sheet for an ultra-thin container, which is soft and has good ductility and achieves excellent flange formability.

[0006]

DISCLOSURE OF THE INVENTION The present invention relates to a method of manufacturing a steel sheet for an ultra-thin container having good ductility, particularly local ductility, at a relatively low annealing temperature which does not hinder the sheet passing property of a continuous annealing line. As a means of the above, the present invention has been completed as a result of repeated investigations focusing on the rolling temperature during rolling after pickling.
The gist is to apply a specific amount or more in the total strain of rolling after pickling at a temperature higher than the normal rolling temperature range and obtain a steel sheet with excellent local ductility at a relatively low annealing temperature. The components for this purpose, the rolling reduction after pickling, and the rolling temperature conditions are limited.

That is, the present invention provides: (1) C: more than 0.0050% to 0.0400% or less, Si: 0.10% or less, Al: 0.01% to 0.08%, Mn : 0.01 to 0.50%, P: 0.02% or less, S: 0.002% to 0.02%, N: 0.0040% or less, with the balance being iron and unavoidable impurities The slab is hot-rolled, and cold-rolling is performed after pickling, and rolling is performed in which a strain of 50% or more of which is converted into logarithmic strain at a temperature of 100 to 500 ° C. is applied, and 550 to 550. A method for producing a steel sheet for an ultrathin container excellent in formability of a can, characterized by annealing at 650 ° C. (2) By weight%, C: 0.0050% or less, Si: 0.10% or less, Al: 0.01% to 0.08%, Mn: 0.01 to 0.50%, P: 0. 02% or less, S: 0.002% ~0.02%, N: 0.0040% or less, containing, a slab containing the balance of iron and unavoidable impurities hot rolling, carried out after pickling Cold forming is performed by converting to logarithmic strain, performing rolling in which 50% or more of the strain is imparted at a temperature of 100 to 500 ° C, and annealing at 600 to 700 ° C. Manufacturing method of excellent steel sheet for ultra-thin containers. (3) The method for producing a steel sheet for an ultra-thin container excellent in can formability according to item 2, wherein the steel component further contains Ti: 0.040% or less. (4) The method for producing a steel sheet for an ultra-thin container excellent in can formability according to the above item 2 or 3, wherein the steel component further contains B: 0.0015% or less.

[0008]

Hereinafter, the present invention will be described in detail. First, the components will be described. All components are% by weight. C is preferably low in terms of drawing, ironing, flange formability and the like in the production process of the container, and the upper limit is made 0.0400%. In recent ultra-thin materials, softer materials are required in order to secure flange formability, and it is preferable to reduce C to 0.0050% or less by vacuum degassing or the like. In particular, when a soft material is required, 0.0020
% Or less, it is possible to greatly improve flange formability, drawing, and ironing.

Since Si and P increase strength and deteriorate workability, it is desirable that Si and P are low from the viewpoint of workability.
It was limited to 0.10% or less and P: 0.02% or less. M
Excessive contents of n and S also degrade ductility. However, if one or both are extremely low, the precipitate (MnS) generated in the steel sheet becomes finer, and the ductility of the steel sheet is reduced. Therefore, an upper limit and a lower limit are set, and Mn: 0.01% to 0.50
%, S: 0.002% to 0.020%.

With respect to Al, the influence of Al itself on workability is relatively small. It is an element that needs to be contained at least for deoxidation. Further, the bonding force with N is strong, and nitride (AIN) is formed in the steel sheet. If the nitride becomes fine depending on manufacturing conditions, ductility is extremely deteriorated. If the content is too small, the nitride becomes fine, so the content is limited to 0.01% to 0.08%. N is Al or T
It is desirable to be fixed as nitride by i or the like in order to obtain good ductility. If the content is too large, the amount of residual N or solid nitride as solid solution N increases and the ductility deteriorates, so the content is made 0.0050% or less.

[0011] Ti significantly improves the ductility of a steel sheet by forming carbonitride and reducing solid solution C and N. Therefore, Ti is added particularly in the case of extremely low C of 0.0050% or less. Is desirable. However, excessive addition deteriorates the workability, raises the recrystallization temperature, and necessitates an increase in the annealing temperature, which lowers the continuous annealing passability of the extremely thin material and is disadvantageous in energy cost. Considering the addition cost, Ti:
0.04% or less. Extremely low C and addition of carbide forming elements may deteriorate secondary workability such as flange forming. Therefore, it is desirable to add B as necessary. In this case, an excessive addition deteriorates workability, so the upper limit is made 0.0015%.

The present component steel is subjected to cold rolling after hot rolling and pickling. The hot rolling conditions are not particularly limited, but the winding temperature is 650.
C. or higher is preferred because ductility is good. However, even if the film is wound at room temperature, the effect of the invention due to the limitation of the cold rolling temperature described below is not impaired at all. Although the rolling reduction after the pickling is not particularly limited, it is desirably 90% or more. This is because not only can the productivity of hot rolling be improved by increasing the cold rolling rate, that is, increasing the thickness of the hot rolled sheet, but in general, the higher the rolling reduction rate of rolling after pickling, the better. This is because the recrystallization temperature is lowered and low-temperature annealing becomes possible.

The temperature condition of rolling after pickling is an important requirement in the present invention. It is necessary that at least 50% of the total strain to be applied is converted at logarithmic strain at a temperature of 100 to 500 ° C. in order to obtain good ductility. When the rolling temperature range is lower than 100 ° C., the effect of improving ductility is lost. On the other hand, when the temperature exceeds 500 ° C., the rolling operation is hindered. Rolling in this temperature range does not need to extend over the entire amount of reduction, and as described above, if it extends over 50% in terms of logarithmic strain, the effect of improving ductility appears. This warm rolling may be performed in any of the initial, middle, and late stages of rolling after pickling.

After cold rolling, annealing is performed. This temperature is required to sufficiently recrystallize the rolled structure in order to ensure uniformity of the material properties and workability. 550 ° C. or higher and 650 ° C. or lower. In general, the higher the purity of the steel component, the lower the recrystallization temperature. However, in the case of steel with a C content of 0.0050% or less, which is usually produced by vacuum degassing, a steel that produces cementite with a C content of 0.02% or more In this case, the accumulation of strain during cold rolling differs, and the recrystallization temperature rises. For this reason, in steel in which C is reduced in order to increase ductility, the annealing temperature is limited to 600 ° C. or more and 700 ° C. or less.

At present, in the manufacture of containers, steel which is re-rolled after annealing and hardened by work hardening is sometimes used to increase the strength of the container. According to the method of the present invention, even in such a steel sheet, the ductility before re-cold rolling is improved, so that the effect of improving the flange formability can be obtained. Further, the steel sheet according to the method of the present invention is excellent in ductility as a property before re-cold rolling, but has relatively high yield strength. This is presumably because the crystal grain size of the steel of the present invention is reduced. For this reason, the strength of the can is advantageous, and the re-rolling rolling reduction can be set low. Therefore, even when the DR method is used, the deterioration of the flange formability due to the re-rolling can be suppressed.

As described above, since the present invention exhibits excellent ductility, not only flange formability but also neck workability for reducing the diameter of the opening of the can body and ironing workability for a two-piece can are improved. In addition, the steel sheet of the present invention is usually used as an original sheet for a surface-treated steel sheet, but the surface treatment does not impair the effects of the present invention at all. As the surface treatment for cans, tin, chromium (tin-free) or the like is usually applied. In addition, it can be used as a base plate for a laminated steel sheet to which an organic film, which has been used in recent years, is attached without impairing the effects of the invention.

[0017]

EXAMPLES Steel having the components shown in Table 1 was hot-rolled, cold-rolled, and continuously annealed, and some of the materials were re-cold-rolled to produce a steel sheet having a final thickness of 0.16 mm. Cold rolling is performed continuously in 5 passes, and the temperature is measured at the entrance and exit of each pass. If both the entrance and exit temperatures are within the limited temperature range, all the strain applied in that pass is the limited temperature. If the first half or the second half of the rolling is out of the limited temperature range, it is assumed that the temperature changes linearly during rolling in the roll, and the strain applied within the limited temperature range The amount was calculated.

The evaluation of the material properties was carried out by molding in the same process as the actual can molding by the can molding machine in the laboratory of the present inventors. One was for a three-piece can, and the can body was manufactured by welding, and neck forming and flange forming were performed. In addition, as a material for two-piece cans, drawing, redrawing, ironing, and neck and flange forming were performed. As for neck formability, the ratio of wrinkles generated during neck forming and the degree thereof were compared with those of a conventional material formed simultaneously. Regarding the flange formability, the rate of occurrence of flange cracks was compared with that of the conventional material. The ironing processability was also compared with the conventional material in terms of the processing power during ironing. Table 2 shows the results. As is evident from Table 2, those manufactured within the scope of the present invention have low earring rates.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

As described above, according to the present invention, a steel sheet excellent in ductility, particularly local ductility, can be manufactured even at a relatively low annealing temperature. For this reason, for materials for ultra-thin containers, productivity can be improved by improving the sheetability during continuous annealing during the production of steel sheets, and the neck formability, flange formability and ironing formability are extremely good during can making. Becomes

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C21D 9/46-9/48 C21D 8/00-8/10 C22C 38/00-38/60

Claims (4)

(57) [Claims] 1. In weight%, C: more than 0.0050% to 0.0400% or less, Si: 0.10% or less, Al: 0.01% to 0.08%, Mn: 0.01 to 0% .50%, P: 0.02% or less, S: 0.002% to 0.02%, N: 0.0040% or less, and hot-rolling a slab consisting of iron and unavoidable impurities Then, in cold rolling performed after pickling, rolling is performed in which a logarithmic strain is converted and 50% or more of the strain is imparted at a temperature of 100 to 500 ° C, and annealing is performed at 550 to 650 ° C. A method for producing a steel sheet for an ultra-thin container excellent in formability of a can characterized by the following. 2. In% by weight, C: 0.0050% or less, Si: 0.10% or less, Al: 0.01% to 0.08%, Mn: 0.01 to 0.50%, P: 0.02% or less, S: 0.002% ~0.02%, N: 0.0040% or less, containing, a slab containing the balance of iron and unavoidable impurities hot rolling, after pickling Wherein the cold rolling is performed at a temperature of 100 to 500 ° C. in the form of a logarithmic strain, and annealing at 600 to 700 ° C. is performed. Method for manufacturing ultra-thin steel sheets for containers with excellent heat resistance. 3. The steel component further contains Ti: 0.040%
3. The method for producing a steel sheet for an ultra-thin container according to claim 2, which comprises: 4. B: 0.0015% as a steel component
The method for producing a steel sheet for an ultra-thin container excellent in formability of a can according to claim 2 or 3, wherein: