JP3422862B2 - Manufacturing method of original plate for high strength container - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a base plate for a high-strength container having excellent can-making properties. 2. Description of the Related Art Container original plates are made of T1 to T6 and DR8.
Standardized at strength (hardness) levels such as DR10. If the composition system is changed to satisfy these standards, the number of steel types will increase, and in the normal steelmaking process, surplus materials will be generated because of melting in units of several hundred tons, which will increase the management cost, and as a result, Manufacturing costs increase. Therefore, the number of steel types is usually reduced as much as possible, the manufacturing process conditions are changed, and a wide range of strength levels is created. [0003] Techniques for producing strength include annealing temperature,
Control techniques such as a cooling rate and a 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 Patent Publication No. 1-52451 or the like, in temper rolling, it is possible to selectively produce strength in a wide range. However, when the temper rolling reduction is increased, 1) the anisotropy of the steel sheet becomes more and more 2) The yieldability (YP) is high, and the factors that deteriorate the formability such as the ductility are deteriorated and the can-making properties are impaired. . In particular, in the case of a high-strength steel sheet for a container having a high temper rolling reduction, wrinkles are remarkably generated during neck processing and bottom processing of a DI can, and the can-manufacturability is significantly deteriorated. SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a high-strength container original plate having excellent can-making properties in an economical manner. 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 step. And it was found that by optimizing these processing conditions, a high-strength container base plate having excellent can-making properties can be produced. That is, the gist of the present invention is that a steel sheet for a container is subjected to recrystallization annealing by continuous annealing, followed by carburizing and nitriding treatment, and further temper rolling of 0.5% or more and 10% or less. In the method for producing a container original plate, the amount of carburization and nitriding is controlled to produce different hardness ranges of 50 to 80 in HR30T. Next, the limiting conditions of the present invention will be described. The only condition that the steel sheet was recrystallized before nitriding, carburizing, or carburizing / nitriding was that the steel was recrystallized if nitriding, carburizing, or carburizing / nitriding was performed before the recrystallization was completed. Is remarkably suppressed, and an unrecrystallized structure may remain to cause significant deterioration in workability. [0008] As for the strength, the C and N are infiltrated from the surface of the steel sheet after the recrystallization treatment, and the strength is enhanced by solid solution hardening and precipitation strengthening. Methods for infiltrating C and N from the steel sheet surface include nitriding, carburizing, and carburizing and nitriding. In order to increase the strength of the steel sheet for containers in industrial production, economically, and relatively uniformly in the longitudinal direction and the width direction of the steel sheet coil by these methods, it is necessary to carry out a continuous annealing process. [0009] The reason why the strength range to be separately formed is from 50 to 80 in HR30T is that if it is less than 50, the characteristics as a high-strength steel sheet cannot be obtained, and industrial value such as reduction in sheet thickness cannot be sufficiently exhibited. If it is 80 or more, the workability is deteriorated, and a problem easily occurs in the moldability of the can. With respect to the time and temperature of the nitriding treatment, carburizing treatment or carburizing / nitriding treatment, it is not necessary to set any limited conditions in the spirit of the present invention in that the strength is separately formed. Preferably, the temperature range is 650 ° C. or higher where the diffusion of C and N proceeds rapidly. The upper limit of the temperature is not particularly limited. However, when the sheet is passed through a continuous annealing facility, when the sheet is passed through a thin material such as a container at a high temperature, the shape of the steel sheet deteriorates. It is desired to do. There is no particular limitation on the processing time, but from the viewpoint of productivity, it is desirably several seconds to several minutes. The control of the amounts of C and N introduced by the nitriding treatment, carburizing treatment or carburizing / nitriding treatment can be adjusted not only by the temperature but also by the amount of the ambient gas such as ammonia, carbon monoxide gas and methane gas. The temper reduction ratio is limited to 0.5% or more and 10% or less because the shape correction after annealing cannot be sufficiently performed at a temper reduction ratio of 0.5% or less. On the other hand, the upper limit is 1
The reason why the ratio of 0% is set is that when the temper rolling ratio is further increased, the deterioration of the can-making property due to the increase in the strength becomes remarkable, and the formability of the present invention is better than that of the material prepared separately by the work hardening type. Is lost. Examples of the present invention will be described together with comparative examples.
Using a steel type D shown in Table 1, a material (◇) nitrided during continuous annealing and a material (◆) that has been subjected to temper rolling to increase the strength are produced, and are used as an index of the flange workability during can forming. FIG. 1 shows the results of the hole expanding test. The hole expansion test was performed using a conical die having a vertex angle of 30 ° C., a wrinkle pressing force of 60 tons, and an initial hole diameter of 20 mm. As is apparent from this figure, the nitrided material is more excellent in hole expanding property than the temper rolled material having the same hardness. Here, the nitride material is heated at a rate of 10 ° C./sec, held at 750 ° C. for 30 seconds, and then nitrided at the same temperature for 40 seconds by changing the ammonia concentration from 1% to 10% to increase the strength. planned. The temper rolling rate of the nitrided material is 1.
5%. Next, a method for increasing the strength of a steel sheet having the composition shown in Table 1 when a steel sheet for a container was manufactured, the hardness of the steel sheet and the temper reduction ratio, and the workability during can making are described. It is shown in Table 2. The test steel is a continuous cast slab material with a thickness of 250 mm, which is heated between 1100 ° C and 1250 ° C, hot-rolled in the γ range, cold-rolled, and recrystallized by continuous annealing. Subsequently, nitriding treatment, carburizing treatment or carburizing / nitriding treatment was performed. The amounts of C and N introduced by the treatment were adjusted by the treatment time and the concentrations of ammonia, carbon monoxide gas, and methane gas, and the strength was separately formed. On the other hand, the temper rolled material, which is a comparative material, adjusts the cold rolling rate and the temper rolling rate to make it equal to the nitriding, carburizing or carburizing / nitriding material to compare the hardness, and the final sheet thickness to the treated material. Similarly 0.2
mm. [0015] The evaluation of processability in the manufacture of containers was carried out using DI (Dra
wing & Ironing) Neck workability of cans and welded cans, and flange workability of DI cans. As a quantitative evaluation, 100 cans were manufactured using a lab canning machine, and the rate of defective cans at that time was calculated as%.
Indicated by The tin plating amount is 2.8 g per square meter for DI cans and 1 g per square meter for welded cans. The neck processing was performed using a spin necker. In this embodiment, a material in which strength is obtained by nitriding treatment, carburizing treatment or carburizing / nitriding treatment and temper rolling is shown in comparison. The odd-numbered experimental numbers are nitriding, carburizing or carburizing / nitriding materials, and the even-numbering materials are materials whose strength has been increased by temper rolling. In Experiment Nos. 1, 3, 5, 7, 9, 11, 13, and 15, which are within the scope of the present invention, both the welded can and the DI can have good neck workability, and the DI can has excellent flange workability. On the other hand, any temper-rolled material adjusted to the same strength level as the nitriding, carburizing or carburizing / nitriding material has inferior can moldability as compared with the material of the present invention. [Table 1] [Table 2] Industrial Applicability According to the present invention, it is possible to reduce the deterioration of the flange workability and neck workability due to the increase in the strength of the steel sheet for containers, thereby realizing a further thinner can material, and The meaning is great.

BRIEF DESCRIPTION OF THE DRAWINGS [FIG. 1] A material in which the relationship between the hole expansion ratio, which is a quantitative index of flange workability, and HR30T, which is an index for increasing the strength of a steel sheet, is increased in strength by nitriding, and a temper reduction ratio. In contrast, a material whose strength is changed to increase the strength is shown.

Claims (1)

(57) [Claims 1] A steel sheet for a container is subjected to recrystallization annealing by continuous annealing, followed by carburizing and nitriding, and further 0.5%
A method for producing an original plate for a container, characterized in that when producing by subjecting to a temper rolling of at least 10% or less, the amount of carburization and nitriding is controlled so that a hardness range of 50 to 80 is selected for HR30T.