摘要 |
PROBLEM TO BE SOLVED: To provide an ultrahigh-strength steel sheet superior in hydrogen-embrittlement resistance and workability. SOLUTION: The ultrahigh-strength steel sheet superior in hydrogen-embrittlement resistance comprises, by mass, over 0.25 to 0.60% C, 1.0-3.0% Si, 1.0-3.5% Mn, 0.15% or less P, 0.02% or less S, 1.5% or less (excluding 0%) Al, and the balance iron with unavoidable impurities; has a metallurgical structure after the sheet has been stretch-worked at a stretching rate of 3%, in which retained austenite occupies 1% or more by an area rate with respect to the total structure, and in which crystal grains of the retained austenite have an average axial ratio (major axis/minor axis) of 5 or higher, an average minor axis length of 1μm or less, and spaces of 1μm or less at the nearest parts between the neighboring crystal grains; and has further a tensile strength of 1,180 MPa or higher. COPYRIGHT: (C)2006,JPO&NCIPI
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