| 摘要 |
PROBLEM TO BE SOLVED: To provide a high tensile strength steel sheet which has excellent base metal toughness and HAZ (Heat Affected Zone) toughness regardless of its high strength satisfying the tensile strength of≥780 MPa. SOLUTION: The steel sheet has components comprising, by mass, 0.010 to 0.080% C, 1.10 to 3.00% Mn, 0.02 to 0.50% Si,≤0.030% P,≤0.010% S,≤0.200% Al, 0.10 to 1.60% Cu, 0.40 to 2.50% Ni, 0.30 to 2.00% Cr, 0.10 to 1.10% Mo, >0.008 to 0.030% Ti and≤0.0100% N, and the balance Fe with impurities, and in which AS≥3.60 and DL≤2.80 are satisfied, and has a structure consisting mainly of bainitic ferrite, and in which the average value of the diameters of the equivalent circle in the bainite blocks is≤5μm; wherein, AS=[Mn]+[Ni]+2×[Cu], DL=2.5×[Mo]+30×[Nb]+10×[V], and [X] denotes the content (mass%) of the element X. COPYRIGHT: (C)2005,JPO&NCIPI
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