| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for manufacturing a cold-rolled steel sheet which has both of superior elongation and superior formability for an extension flange, a tensile strength as high as 980 MPa or higher, and a high yield ratio. SOLUTION: A steel slab for the cold-rolled steel sheet comprises, by mass%, 0.02% C or less, 0.3% Si or less, 0.5-2.0% Mn, 0.06% P or less, 0.005% S or less, 0.06% Al or less, 0.006% N or less, 0.15-0.40% Ti and the balance Fe with unavoidable impurities. The method for manufacturing the cold-rolled steel sheet having a high yield ratio, high tensile strength and superior workability comprises the steps of: heating the steel slab to 1,150°C or higher; then hot-rolling it at a finishing temperature of 880°C or higher; winding up the hot-rolled plate at a winding up temperature of 400 to 700°C; pickling the plate; cold-rolling it; and then annealing the cold-rolled steel sheet in a carburizing atmosphere at 600 to 720°C. COPYRIGHT: (C)2007,JPO&INPIT
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