| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel sheet having a tensile strength of 880 MPa or higher in the direction rectangular to the direction of rolling and a yield ratio of 0.80 or higher and suited for automobile underbody parts, and to provide a method for production thereof. SOLUTION: The steel comprises 0.04 to 0.17% C, at most 1.1% Si, 1.6 to 2.6% Mn, at most 0.05% P, at most 0.02% S, 0.001 to 0.50% Al, at most 0.02% N, at most 0.11 to 0.30% V, and 0.07 to 0.25% Ti, and optionally contains at least one element selected from the group consisting of (1) at most 0.10% Nb, (2) at most 0.01% Ca, and (3) at least one of at most 1.0% Cr, at most 1.0% Mo, at most 1.0% Cu, and at most 1.0% Ni, with the balance being iron and unavoidable impurities. The steel is produced by heating bloom to 1,100°C or higher, subjecting the heated bloom to rough rolling, completing finish rolling at 750°C or higher, cooling the finish-rolled product at an average cooling rate of at least 5°C/sec, and winding the cooled product at 400 to 650°C. It is also possible that the rough rolling is performed after the heating of the bloom, the rough bar after the rough rolling is heated or kept at the same temperature, and the finish rolling is completed. COPYRIGHT: (C)2005,JPO&NCIPI
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