JPH08176788A - Production of steel plate for vessel - Google Patents

Abstract

PURPOSE: To economically manufacture the steel plate for a high-strength vessel having excellent vessel producibility by subjecting steel having a specific compsn. consisting of C, N, Mn, Si, P, Al, S and Fe to cold rolling and recrystallization annealing, then to a specific nitriding treatment and temper rolling. CONSTITUTION: The steel contg. <=0.1wt.% C, <=0.01% N, <=0.6% Mn, <=0.2% Si, <=0.02% P, 0.005 to 0.2% Al and <=0.02% S and consisting of the balance Fe with inevitable impurities is subjected to the recrystallization annealing in a continuous annealing furnace after cold rolling. The steel plate is thereafter subjected to the nitriding treatment, carburization treatment or carbonitriding treatment. This treatment is executed in a relatively short period at about 650 to 850 deg.C in a continuous annealing process. The increase amt. of the total ratio of N and C is specified to 20 to 200ppm in thickness average. This steel sheet is thereafter subjected to temper rolling of 0.5 to 10%.

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 steel sheet for a high strength container having excellent can making properties.

[0002]

2. Description of the Prior Art Steel sheets for containers are T1 to T6 and DR8.
To DR10 are standardized at strength (hardness) levels. If the composition system is changed so as to satisfy these standards, the number of steel types will increase, and in the normal steelmaking process, surplus materials for melting in hundreds of tons are likely to occur, resulting in high management costs. As a result, the manufacturing cost increases. Therefore, usually, the steel grade is reduced as much as possible, the manufacturing process conditions are changed, and a wide range of strength levels are created.

Annealing temperature,
Control technologies such as cooling rate and temper rolling rate in continuous annealing have been developed, but the former two have a narrow range of production. On the other hand, as disclosed in Japanese Examined Patent Publication No. 1-52451 and the like, in temper rolling, it is possible to make different strengths over a wide range. However, when the temper rolling ratio becomes large, 1) the anisotropy of the steel sheet increases, 2) the yield point (YP) is high, and the factors that deteriorate the formability such as the deterioration of ductility become strong and hinder the can-making property. To do. In particular, in the case of a steel plate for a high-strength container having a high temper rolling rate, wrinkles are significantly generated during neck processing or bottom processing of a DI can, and the can-making property is significantly deteriorated.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing a steel sheet for a high-strength container which has an excellent can-making property by an economical method.

[0005]

Means for Solving the Problems The present inventor has studied a technique for producing a wide range of strength levels by performing nitriding, carburizing, or carburizing / nitriding in a continuous annealing process. Then, they have found that by optimizing these processing conditions, a steel sheet for a high-strength container having excellent can-making properties can be produced.

The gist of the present invention is the weight ratio, C
: 0.1% or less, N: 0.01% or less, M
n: 0.6% or less, Si: 0.2% or less, P
: 0.02% or less, Al: 0.005% or more,
0.2% or less, S: 0.02% or less, balance F
After cold rolling of steel consisting of e and unavoidable impurities, it is recrystallized in a continuous annealing furnace and then subjected to nitriding, carburizing or carburizing / nitriding to increase the total amount of N and C. The method for producing a steel sheet for containers is characterized in that the average is changed from 20 ppm to 200 ppm, and then temper rolling of 0.5% or more and 10% or less is performed.

As a technique for nitriding the surface layer to obtain a high-strength cold-rolled steel sheet, JP-A-3-243757 discloses an invention in which the surface layer of a cold-rolled steel sheet containing Ti is nitrided. The present inventors have completed the present invention based on this technique. That is, in the steel sheet for containers, unlike the case of the cold-rolled steel sheet, it is effective not only by nitriding but also by carburizing, and does not contain Ti, nitrogen, not only the surface layer of carbon,
We have found that the ability to make cans is better when they penetrate into the interior.

Next, the limiting conditions of the present invention will be described. First,
The conditions for limiting the components will be described. C, N, Mn, S, A
The reason why the upper limit of l is limited is that workability deteriorates. The grounds for limiting the upper limits of P and Si are
This is because the corrosion resistance is deteriorated by adding more than this. The lower limit of the amount of Al added was determined by the conditions necessary for sufficient deoxidation.

Next, the limitation of manufacturing conditions will be described. The limiting condition that the steel sheet is recrystallized before nitriding treatment, carburizing treatment or carburizing / nitriding treatment is that recrystallization occurs if nitriding treatment, carburizing treatment or carburizing / nitriding treatment is performed before recrystallization is completed. Is remarkably suppressed, and a non-recrystallized structure may remain to cause remarkable deterioration of workability.
In order to perform the nitriding treatment, the carburizing treatment, or the carburizing / nitriding treatment in the continuous annealing process, it is necessary to finish the treatment in a relatively short time. Therefore, the temperature range is preferably 650 ° C. or higher and 850 ° C. or lower. That is, at 650 ° C or lower, the diffusion rate is low,
The amount of C and N entering the steel plate is small. Further, at 850 ° C. or higher, ammonia used for nitriding decomposes in the atmosphere, and effective nitriding cannot be performed, and annealing at high temperature itself
When a thin plate such as a container steel plate is passed, a defective shape is likely to occur, which is not desirable.

The increase in the total amount of N and C is 20 pp in average plate thickness.
The reason why the m is limited to 200 ppm is that the effect of increasing the strength is small with an increase of 20 ppm or less.
This is because if the content is 0 ppm or more, the strength becomes too high and the moldability deteriorates significantly. Control of the amounts of C and N introduced by the nitriding treatment, the carburizing treatment, or the carburizing / nitriding treatment is adjusted not only by the temperature but also by the amount of the atmosphere gas such as ammonia or methane gas.

The temper rolling rate is limited to 0.5% or more and 10% or less because the shape rolling after tempering cannot be sufficiently corrected at the temper rolling rate of 0.5% or less. On the other hand, the upper limit is 1
The reason for setting it to 0% is that if a temper rolling rate higher than this is added, the anisotropy increases and the can-making property deteriorates.

[0012]

EXAMPLES Examples of the present invention will be described together with comparative examples.
Using the steel type B shown in Table 1, a material nitrided in continuous annealing (○) and a material that has been temper-rolled to increase strength (●) were manufactured, and a wrinkle holding force of 1 ton, punch diameter of 30 mm, drawing Ratio 1.
Fig. 1 shows the state of wrinkling on the side surface of the cup when drawn in Fig. 3 with Rmax on the vertical axis and HR30T on the horizontal axis. As is clear from this figure, the nitrided material is superior in wrinkle resistance to the temper-rolled material having the same hardness. Here, the nitriding material changes the ammonia concentration from 1% to 10%,
Higher strength was achieved. The temper rolling ratio of the nitrided material is 1.5%.

Next, Table 2 shows the manufacturing conditions for manufacturing a steel sheet for containers using the steels having the composition shown in Table 1, and the hardness and workability when manufacturing cans. The test steel is a continuously cast slab material with a thickness of 250 mm, which is heated from 1100 ° C to 1250
After heating between 0 ° C., hot rolling in the γ region, cold rolling, recrystallization treatment by continuous annealing, and subsequent nitriding treatment, carburizing treatment, or carburizing / nitriding treatment. The amount of C and N introduced by the treatment was adjusted by the treatment time and the concentrations of ammonia and methane gas. The plate thickness was adjusted to 0.2 mm.

DI (Dra
Wing & Ironing) Cans and welded cans are arranged according to their workability. As a quantitative evaluation, 100 cans were manufactured by a can manufacturing machine in a laboratory, and the defective can generation rate was shown in%. The tin plating amount is 2.8 g per square meter for DI cans and 1 g per square meter for welded cans. Neck processing was performed using a spin necker.

[0015]

[Table 1]

[0016]

[Table 2]

Experiment numbers 1, 2, within the scope of the present invention
3,5,6,7,9,10,11,14 are welding cans, DI
Both cans have good neck workability. On the other hand, Experiment No. 5 in which the amount of N introduced by nitriding was within the range of the present invention
Then, wrinkles occurred during neck processing. Further, the material of Experiment No. 8 which was strengthened only by work hardening had a high wrinkle occurrence frequency. Experiment No. 13 shows that wrinkles are generated even with the nitrided material if the temper rolling ratio exceeding the range of the present invention is increased.
Experiment No. 12 using Steel E in which the amount of C was added within the range of the present invention also had poor workability and wrinkles occurred. In Experiment No. 15, as can be seen by comparing with the untreated material shown in Experiment No. 16, the nitriding did not sufficiently enhance the strength.

[0018]

Industrial Applicability According to the present invention, it is possible to reduce the wrinkle sensitivity associated with the increase in strength of the steel sheet for containers, and it is possible to realize further thinning of the can material, which is of great industrial significance.

[Brief description of drawings]

[Fig. 1] The relationship between Rmax, which is a quantitative index of wrinkles, and HR30T, which is an index of strength enhancement of steel sheet, in comparison with a material strengthened by nitriding and a material strengthened by changing the temper rolling rate. Show.

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Claims (1)

[Claims] 1. By weight ratio, C: 0.1% or less, N: 0.01% or less, Mn: 0.6% or less, Si: 0.2% or less, P: 0.02% or less, Al : 0.005% or more, 0.2% or less, S: 0.02% or less, and steel that is composed of the balance Fe and unavoidable impurities, after cold rolling and recrystallization annealing in a continuous annealing furnace. Nitriding treatment, carburizing treatment or carburizing / nitriding treatment to increase the total amount of N and C from 20ppm to 200ppm in sheet thickness average, and then temper rolling at 0.5% or more and 10% or less. A method of manufacturing a steel plate for a container, which is characterized.