| 摘要 |
PROBLEM TO BE SOLVED: To provide an ultrahigh-strength steel sheet which has excellent hydrogen embrittlement resistance and workability. SOLUTION: The ultrahigh-strength steel sheet having excellent hydrogen embrittlement resistance and workability is composed of a steel sheet having a composition comprising, by mass, 0.05 to 0.25% C, 1.00 to 2.5% Si, 2.0 to 4.0% Mn, ≤0.1% (excluding 0%) P, ≤0.05% (excluding 0%) S, 0.01 to 0.15% Al, 0.003 to 0.10% Ti and ≤0.01% (excluding 0%) N, and the balance iron with inevitable impurities, and having a composite structure composed of 10 to 50 area% ferrite and ≥50 area% martensite, and in which the average grain size of the ferrite grains is ≤2.0 μm, and also, the average aspect ratio of the ferrite grains is ≤2.0, and having a tensile strength of ≥1,100 MPa. COPYRIGHT: (C)2010,JPO&INPIT
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