High tensile strength steel for container and producing method of the same

Abstract

A steel sheet for containers that has a hardness of 500 MPa or more and superior workability and a method for producing the steel sheet are provided. A steel containing, in percent by mass, 0.01% to 0.05% carbon, 0.04% or less silicon, 0.1% to 1.2% manganese, 0.10% or less sulfur, 0.001% to 0.100% aluminum, 0.10% or less nitrogen, and 0.0020% to 0.100% phosphorus, the balance being iron and incidental impurities, is subjected to hot rolling at a finishing temperature of (Ar₃ transformation temperatute−30)° C. or more and a coiling temperature of 400° C. to 750° C., is subjected to pickling and cold rolling, is subjected to continuous annealing including overaging treatment, and is subjected to second cold rolling at a reduction rate of 20% to 50%, thus providing a high-strength steel sheet for containers that has a tensile strength of 500 MPa or more and a proof stress difference between width and rolling directions of 20 MPa or less.

Description

TECHNICAL FIELD[0001]The present invention relates to high-strength steel sheets for containers suitable as container materials to be subjected to diameter-shape reduction or expansion processing after three-piece processing, such as welding, or two-piece processing, such as DI, and also relates to methods for producing such steel sheets.BACKGROUND ART[0002]For cost reduction, as well as reductions in material usage and environmental load, product development has recently been proceeding toward a reduction in the product thickness of steel materials (steel sheets) serving as raw materials.[0003]At the same time, because reducing the product thickness decreases rigidity, the strength of the steel materials must be increased to compensate for the decrease in rigidity. An increase in the strength of the steel materials, however, causes a problem in that such hardened materials may be cracked during flange forming or neck forming.[0004]To solve the above problem, various production meth...

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Benefits of technology

[0026]In addition, although not specifically limited, the thickness is preferably 0.30 mm or less, more preferably 0.20 mm or less, in view o

Problems solved by technology

An increase in the strength of the steel materials, however, causes a problem in that such hardened materials may be cracked during flange forming or neck forming.

The method of Patent Document 1, however, has a problem in that it is difficult to efficiently, process the steel into thin products, which are therefore not easy to manufacture, and the steel also tends to have a poor appearance, because it contains 0.02% by weight or less phosphorus so that flange formability, neck formability, and corrosion resistance are not degraded and also because the reduction rate in the secondary cold rolling is 15% to 30%.

Another problem is that a crack may occur in a surface layer of a slab, thus decreasing a product yield.

Furthermore, the steel is difficult to stabl