| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-strength steel sheet exhibiting excellent PWHT (post-weld heat treatment) resistance. SOLUTION: Disclosed is a high-strength steel sheet having a componential composition comprising 0.03 to 0.07% C, 0.01 to 0.5% Si, 1.5 to 2.5% Mn, 0.1 to 0.5% Mo,≤0.08% Al, 0.005 to 0.035% Ti and 0.005 to 0.07% Nb, and in which Ceq value (mass%)=C+Mn/6+(Cu+Ni)/12+(Cr+Mo+V)/5 and P value (atomic%)=[Mo]+[Ti]+[Nb]+[V] satisfy 9×Ceq value+4×P value≥4.8, and also, 0.6 (atomic%)≤[C]/([Mo]+[Ti]+[Nb]+[V])≤1.7 (atomic%) is satisfied, and essentially composed of a bainitic structure in which the fraction of insular martensite is≤2%, wherein, (Ti and/or Nb) compound carbides essentially composed of Mo with an equivalent circle diameter of≤10 nm are dispersed by≥30 pieces per 1μm<SP>2</SP>, and the total precipitation amount of the compound carbides is≥0.03 mass%. COPYRIGHT: (C)2009,JPO&INPIT
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