JP2980488B2 - Method for producing steel sheet for low earring container - 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 a plating base sheet for an ultra-thin container having excellent earring resistance.

[0002]

2. Description of the Related Art From the viewpoint of weight reduction and resource saving, there is a demand from the market for an extremely thin original plate for a container. In response,
Material suppliers are making efforts to achieve ultra-thin by increasing the cold-rolling rate in the conventional hot rolling-cold rolling-annealing-temper rolling process. However, there are two major problems here. One is that the sheet thickness after cold rolling is extremely thin, so that if annealing is performed by continuous annealing, it is difficult to pass through the sheet, the shape will be deteriorated, and in some cases, the sheet will break, which will be a major problem not only in quality but also in operation. Sometimes. As a technique for avoiding this problem, in Japanese Patent Publication No. 1-52451, the thickness of the sheet after cold rolling is not reduced to an extremely small value, but is set to about 0.3 mm, and after annealing, 10 to 50% larger than that of the conventional temper rolling. A technique for reducing the thickness to a target sheet thickness by performing cold rolling at a rolling reduction of 0.1 mm is disclosed. However, the steel sheet manufactured at such a large secondary reduction ratio has a large anisotropy, and the DI (drawing and
DI in two-piece cans manufactured by ironing) processing
After processing, unevenness of the height of the can body called an earring occurs remarkably in the opening (the earring rate is an index that quantitatively expresses the earring, and this is obtained by subtracting the minimum value from the maximum value of the can body height). If the earring is large, trimming is necessary to make the can body height uniform, which not only reduces the yield but also reduces the number of steps. The cost increases because of the increase. The problem of the earring tends to become apparent not only when the cold rolling reduction performed after annealing is large, but also when the rolling reduction before cold annealing is large.

In order to solve this problem, a means for reducing the thickness of the hot rolled sheet can be considered. However, thinning of hot-rolled sheets causes a decrease in finishing temperature and an increase in rolling load, which not only causes problems in quality and stability of threading, but also increases industrial pickling costs due to an increase in surface area. Not an attractive means.

[0004]

SUMMARY OF THE INVENTION From the state of the art, it is an object of the present invention to provide a method for producing a steel sheet for an ultra-thin container with small earrings by adjusting the components in the steel and using an economical rolling method. And

[0005]

The inventors of the present invention have studied in detail the effects of components and manufacturing conditions on the earrings of an ultra-thin container steel sheet. It was found that by adding, the texture can be effectively controlled and the earring can be significantly reduced.
The present invention is based on these findings, and has the following features. That is, C: 0.003 by weight ratio.
%, 0.08% or less, Si: 0.2% or less, M
n: 0.6% or less; Sn: 0.005% or more;
2% or less, Al: 0.005% or more, 0.1% or less,
N: A steel containing 0.015% or less, with the balance being Fe and unavoidable impurities, is hot-rolled at a temperature of 840 ° C. or more, rolled, pickled, then cold-rolled with the thickness th of a hot-rolled sheet. The relationship of (th−tf) / th <0.95 is established between the final sheet thicknesses tf after the recrystallization annealing and the subsequent cold rolling, and the cold rolling rate after the recrystallization annealing is 0.5%. As described above, the present invention provides a method for producing a steel sheet for a low earring container, wherein 30% or less and tf are 0.22 mm or less and 0.14 mm or more.

Next, the limiting conditions of the present invention will be described. First,
The conditions for limiting the components will be described. The most important element in the present invention is Sn, and the addition of a trace amount of Sn can reduce the earring within the range of the hot-rolled sheet thickness and the cold-rolling rate at which an ultra-thin container steel sheet can be economically manufactured. The lower limit of the amount of Sn added is set to 0.005%, because the addition of less than this amount causes the addition of S
This is because the effect of n addition is not sufficiently exhibited, and no remarkable decrease in earring is observed. In addition, the upper limit of the amount added is 0.1.
The reason for setting it to 2 is that the addition of more than this saturates the effect of reducing the earring, and unnecessarily increases the alloy cost.

The reason why the C content exceeds 0.003% is that if the C content is less than the lower limit, an increase in strength cannot be achieved in a coating baking process performed in a coating process after can formation. This increase in strength is called BH (Bake Hardening), and is a phenomenon that occurs when the interstitial elements C and N adhere to dislocations. Since the strength increases after processing, it can be easily formed with a low load during processing. Since the strength of the can is increased after molding, it is an industrially attractive property. The upper limit of the C content is set to 0.08%, because the addition of more than this will deteriorate the workability and increase the frequency of occurrence of defects such as flange cracks during molding.

[0008] If a large amount of N is added, bubbling occurs at the time of steel making and the material is deteriorated.
Limited to 5%. In order to effectively utilize the Al content as a deoxidizing component, it is necessary to add at least 0.005% or more in steel. Further, since the addition of a large amount not only increases the cost but also deteriorates the workability, the upper limit of the addition amount is set to 0.1%. The amounts of Si and Mn to be added to Si:
The reason for limiting the content to 0.2% or less and Mn: 0.6% or less is that if these alloys are added any more, they may cause deterioration in workability and hinder corrosion resistance.

Next, the limitation of the manufacturing conditions will be described. The reason why the hot rolling finish temperature is set to 840 ° C. or higher is that, in the component of the present invention, when the finish rolling is performed at a temperature lower than this temperature, a part or all of the steel becomes a ferrite structure at the time of finish rolling, and the former tends to cause variation in properties. In the latter case, the earring rate is increased.

In the relationship between the sheet thickness th of the hot-rolled sheet and the final sheet thickness tf, (th-tf) / th <0.95 is set as the limiting condition as shown in FIG. This is because the steel of the present invention exhibits excellent earring resistance. This is considered to be due to the interaction with the addition of Sn to form a more favorable texture by reducing the earring rate. Here, FIG.
As shown in, even if the thickness reduction of th-tf is achieved only by cold rolling before recrystallization annealing, it is achieved by a combination of cold rolling before recrystallization annealing and cold rolling after recrystallization annealing. However, almost the same effect is exhibited in the earring resistance. The reason why the cold rolling ratio after the recrystallization annealing is limited to 0.5% or more and 30% or less is that a cold rolling reduction of 0.5% or less does not provide a sufficient tempering effect. On the other hand, if the cold rolling rate exceeds 30%, the probability of forming defects such as bottom wrinkles, neck wrinkles, flange cracks, and tear-off during DI processing increases. The reason for limiting the final sheet thickness tf to 0.22 mm or less and 0.14 mm or more is that if the final sheet thickness tf is 0.22 mm or more, the original goals of weight reduction and resource saving cannot be effectively achieved. is there. Further, when the final plate thickness tf is 0.14 mm or less, the rigidity of the can bottom becomes too small, and the shape changes significantly due to the internal pressure of the can.

In the method for producing steel of the present invention, a casting-hot rolling route (either directly hot rolling after casting, or after casting,
The effect of the reheating in the heating furnace), the heating conditions of hot rolling, the winding temperature, and the like are relatively small, and thus there is no particular limitation. Regarding the annealing, since the predetermined characteristics can be achieved if the steel sheet is recrystallized, there is no need to particularly limit the annealing speed and the like.

[0012]

EXAMPLES Table 1 shows the chemical components of the steel of the present invention and the comparative steel.
Table 2 shows the results obtained by examining the earring ratio, the presence or absence of bottom wrinkles, the presence or absence of neck wrinkles, the pressure resistance, and the BH property when DI processing was performed on steel sheets manufactured under the various manufacturing conditions using the materials in Table 1. Show. The occurrence of bottom wrinkles and neck wrinkles was determined by visual observation. The pressure resistance strength is defined by the pressure when the can bottom is inverted by the internal pressure in the can bottom shape shown in FIG.
Here, the test was passed at 0.5 MPa or more. BH amount is 10%
The value of the difference σ2−σ1 between the stress σ1 when the pre-strain was given and the yield stress σ2 measured after aging treatment at 200 ° C. for 30 minutes was evaluated as an index.

In the basic manufacturing process of this embodiment, the continuous cast slab was heated to 1200 ° C., and subjected to continuous hot rolling, followed by pickling, cold rolling, continuous annealing, and temper rolling under high pressure. In Experiment No. 6, the heating temperature was set to 1100 ° C. Experiment No. 2 was manufactured in a pattern of hot rolling directly after continuous casting.
Experiment No. 23 produced a 2 mm thick thin slab by the twin roll method,
After pickling it, cold rolling, continuous annealing and temper rolling under high pressure were performed. In Experiment No. 12, the heating rate was set to 10
Continuous annealing at 00 ° C./sec was performed.

[0014]

[Table 1]

[0015]

[Table 2]

Experiment Nos. 1 to 4, 6, 8, and
10 to 13, 15, 16, 18, 21, and 23 have a low earring ratio, satisfy pressure resistance, have no bottom wrinkles and neck wrinkles, exhibit excellent can moldability, and have a BH amount of 50 MPa or more. Indicated. In Experiment No. 5, in which 35% cold rolling was performed after the recrystallization annealing, wrinkles were observed at the time of can molding, probably because work hardening was large. Experiment No. 7 in which the ratio of (th-tf) / th exceeded the range of the present invention showed a high earring rate. Further, in Experiment No. 9 in which the final plate thickness was 0.12 mm, which was smaller 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. 14 in which the hot-rolled finishing temperature was lower than the range of the present invention had a high earring rate probably because the texture of the hot-rolled sheet was different. C
However, in Experiment No. 17 in which more was added than in the range of the present invention, wrinkles occurred during can molding. Flange cracks were also observed in some parts. In Experiment No. 17 in which the C amount was less than the range of the present invention, a sufficient BH amount could not be obtained. Experiment Nos. 20 and 22, in which the amount of Sn added was less than the range of the present invention, showed a high earring rate.

[0017]

As described above, the present invention provides a new technique capable of reducing the earring which has conventionally been regarded as a problem in the production of a steel sheet for an ultra-thin container, and has great industrial significance.

[Brief description of the drawings]

FIG. 1 shows the relationship between the ratio of (hot-rolled sheet thickness-final sheet thickness) and the ratio of hot-rolled sheet thickness to the earring ratio, comparing the steel of the present invention with a comparative steel.

FIG. 2 is a view showing the shape of the bottom of a can whose pressure resistance is measured.

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁶ , DB name) C21D 9/46-9/48 C21D 8/04 C22C 38/00-38/06

Claims (1)

(57) [Claims] 1. A weight ratio of C: more than 0.003%, 0.08% or less, Si: 0.2% or less, Mn: 0.6% or less, Sn: 0.005% or more, 0.2% Hereafter, steel containing Al: 0.005% or more and 0.1% or less, N: 0.015% or less, and the balance consisting of Fe and unavoidable impurities is hot-rolled at a temperature of 840 ° C or more and wound. The relationship of (th−tf) / th <0.95 is obtained between the thickness th of the hot-rolled sheet and the final thickness tf obtained by cold rolling, recrystallization annealing and then cold rolling after pickling. A method for producing a steel sheet for a low earring container, wherein a cold rolling ratio after recrystallization annealing is 0.5% or more and 30% or less, and tf is 0.22 mm or less and 0.14 mm or more.