| 摘要 |
PROBLEM TO BE SOLVED: To provide an ultrahigh-strength hot rolled steel sheet having excellent workability and particularly a hot rolled steel sheet having excellent stretch-flange formability and ductility and≥900 MPa tensile strength. SOLUTION: The ultrahigh-strength hot rolled steel sheet has a composition consisting of, by mass (with respect to components, the same is applied hereinafter), 0.03 to <0.10% C,≤1.5% (not including 0%) Si, 0.5 to 2.5% Mn, 0.1 to 0.50% Cr, 0.1 to 0.50% Mo, 0.1 to 0.3% Ti and the balance iron with inevitable impurities and satisfying equation [Cr]/[Mo]=0.50 to 1.20 and inequality ([Ti]/48)/([C]/12)≥0.8 (wherein, [Cr], [Mo], [Ti] and [C] represent the respective contents (mass%) of Cr, Mo, Ti and C). Further, this steel sheet has a metallic structure comprising, by area ratio (with respect to the metallic structure, the same is applied hereinafter),≥80% bainitic ferrite and≤10% (including 0%) martensite. COPYRIGHT: (C)2005,JPO&NCIPI
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