| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength steel sheet having≥980 MPa tensile strength and also, high strength and excellent bending property. SOLUTION: This steel sheet has the composition composed of, by mass, 0.1-0.2% C,≤2.0% Si, 1.0-3.0% Mn,≤0.1% P,≤0.05% S,≤1.0% Al, 0.1-3.0% Cr and≤0.01% N and the balance Fe with inevitable impurities, and the steel structure has the composite structure of 20-60% ferrite, 40-80% martensite,≤5% bainite and≤5% residual austenite, in area ratios, and the average grain diameter of the ferrite is 8μm, and≥3/4 area ratio in the martensite is made auto-tempered martensite in which the ferrous carbide of 5-500μm size is precipitated by≥1×10<SP>5</SP>pieces/mm<SP>2</SP>. COPYRIGHT: (C)2010,JPO&INPIT
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