| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for producing a high-strength hot-rolled steel sheet having≥780 MPa of TS and excellent stretch flange formability and stably enabling the fluctuation of the quality in the steel sheet to be small. SOLUTION: The method for producing the high-strength hot-rolled steel sheet having≥780 MPa of the TS, is characterized in that a steel billet having the following element composition, composed by mass% of 0.04-0.15% C, 0.3-1.5% Si, 0.5-2.0% Mn,≤0.06% P,≤0.005% S,≤0.10% Al, 0.05-0.20% Ti and the balance Fe with inevitable impurities, is heated to the heating temperature of 1,150-1,300°C, and after hot-rolling at 800-1,000°C the finish temperature, this hot-rolled steel sheet is cooled at≥55°C/sec cooling rate and successively, after cooling in the temperature range of at least≤500°C thereof, at≥120°C/sec cooling rate under condition of becoming nucleate-boiling cooling, this steel sheet is coiled up at 350-500°C coiling temperature. COPYRIGHT: (C)2010,JPO&INPIT
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