| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength steel sheet, a high strength galvanized steel sheet and a high strength galvannealed steel sheet in a class of 440 to 780 MPa which have excellent strength-flanging properties and impact resistance, and to provide a production method therefor. SOLUTION: The steel sheet has a componential composition comprising, by mass, 0.04 to 0.22% C,≤1.0% Si,≤3.0% Mn,≤0.05% P,≤0.01% S, 0.01 to 0.1% Al and 0.001 to 0.005% N, and, if required, further containing one or more kinds selected from Nb, Ti and V by 0.008 to 0.05% in total, and the balance Fe with inevitable impurities, and has a structure consisting of a ferritic phase as the main phase, and in which the maximum grain size of martensite as a second phase is≤2μm, and also the area ratio thereof is≥5%. Alternatively, the surface of the steel sheet is subjected to galvanizing or galvannealing. COPYRIGHT: (C)2003,JPO
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