| 摘要 |
PROBLEM TO BE SOLVED: To provide a manufacturing method of a high-strength cold-rolled steel sheet achieving a tensile strength of 980 MPa or higher and superior in strength-ductility balance and workability such as stretch-flange-workability. SOLUTION: The method includes preparing a billet containing 0.05-0.20 mass% of C, 0.2-0.8 mass% of Si, 2.0-4.0 mass% of Mn, 0.02 mass% or less of P, 0.0030 mass% or less of S, 0.05 mass% or less of Al, 0.10-1.2 mass% of Ni, and 0.005-0.030 mass% of Ti, hot-rolling and cold-rolling the billet to a plate, applying a continuous annealing at the temperature range of (Ac<SB>3</SB>-50) to (Ac<SB>3</SB>+50)°C, and then cooling the plate to the temperature range of 350-550°C at a cooling speed of 10°C/s or higher and retaining it for 15 sec or longer in this temperature range. COPYRIGHT: (C)2009,JPO&INPIT
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