| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-strength hot-rolled steel sheet having ≥980 MPa tensile strength and excellent balance to the strength-ductility and small softening to a welded heat affecting zone. SOLUTION: A steel slab having the composition composed by mass% of 0.10-0.25% C, ≤1.5% Si, 1.0-3.0% Mn, ≤0.10% P, ≤0.005% S, 0.01-0.5% Al, ≤0.010% N and 0.10-1.0% V and satisfying (10Mn+V)/C≥50 and the balance Fe with inevitable impurities, is made to be a sheet bar by rougher-rolling after heating to ≥1,000°C, and successively, after applying a finish-rolling under condition of the temperature of ≥800°C on the outlet side of the finish-rolling, this sheet bar is cooled to the temperature Ta°C satisfying formula (1): 11,000-3,000[%V]≤24×Ta≤15,000-1,000[%V] (wherein, [%V]: V content (mass%)) within 3 seconds after the finish-rolling is complete at an average cooling rate of ≥ 20°C/s in the temperature range of 400 to 600°C, and wound. COPYRIGHT: (C)2011,JPO&INPIT
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