| 摘要 |
PROBLEM TO BE SOLVED: To obtain a material optimum for short time heat treatment capable of local heat treatment improving formability by specifying the structure and components in steel. SOLUTION: This thin steel sheet for working excellent in formability improving heat treating performance is the one composed of steel contg., by weight, 0.0005 to 0.25% C, 0.01 to 3.0% Si, 0.01 to 3.0% Mn, 0.002 to 0.20% P, 0.001 to 0.03% S and 0.0002 to 0.02% N, in which, in the microstructure of the steel, the total ratio of one or more kinds among crystal grains contg. iron carbides, iron nitrides and iron carbonitrides in the ratio of >=10 pieces/μm2, bainite and martensite is >=7% by an occupance volume rate. As to this steel, the material of the steel can remarkably be changed in the range of heat treatment in a short time, and, moreover, in the case local heat treatment is executed to the part requiring deformation at the time of forming, its formability remarkably be improved. Furthermore, the steel may be incorporated with one or more kinds among Mo, Al, Ni, Cu, Nb, Ti, V, Cr and B in a prescribed range.
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