| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for producing a steel sheet having excellent ductility and fatigue crack propagation stopping properties. SOLUTION: Steel having a composition containing, by mass, 0.04 to 0.16% C, 0.05 to 0.50% Si, 0.5 to 2.0% Mn,≤0.03% P and≤0.01% S, and, if required, one or more kinds of metals selected from≤1.0% Cu,≤2.0% Ni,≤0.5% Cr,≤0.5% Mo,≤0.05% Nb,≤0.1% V,≤0.1% Ti and≤0.005% B, and the balance substantially Fe, and satisfying Ceq≤0.40 is heated at 950 to 1,200°C, and is thereafter rolled at an Ar<SB>3</SB>point or higher at a cumulative draft of≥50%, and, just after that, accelerated cooling is started from an Ar<SB>3</SB>point or higher at a cooling rate of≥10°C/s, subsequently, the cooling is temporarily stopped at Ar<SB>3</SB>-30°C to Ar<SB>3</SB>-100°C, and it is held for (0.2×t/Pcm)s to (0.5×t/Pcm)s, and is thereafter subjected to accelerated cooling to≥500°C at≥10°C/s once more. COPYRIGHT: (C)2006,JPO&NCIPI
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