| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for manufacturing a high-strength cold-rolled steel sheet superior in formability for extension flange. SOLUTION: The high-strength cold-rolled steel sheet comprises, by mass%, 0.03-0.2% C, 2% or less Si, 0.5-3% Mn, 0.1% or less P, 0.01% or less S, 0.01-0.1% sol.Al, and 0.005% or less N and the balance substantially Fe. The manufacturing method comprises smelting a steel having the above composition; hot rolling, pickling and cold rolling it; recrystallization-annealing the obtained steel sheet at an Ac1 temperature or higher; quenching it at a cooling rate of 100°C/s or higher between the quenching-starting temperature and 100°C or lower; when T<SB>1</SB>(°C) is defined as a tempering temperature, rapidly heating the steel sheet to 0.5×T<SB>1</SB>(°C) at a heating rate of 10°C/s or higher; and tempering it at a temperature between 200 and 500°C. The above steel preferably further includes one or two elements of 1% or less Cr and 1% or less Mo, or still further one or more elements among 0.05-0.2% V, 0.0002-0.002% B, 0.005-0.1% Nb and 0.005-0.1% Ti. COPYRIGHT: (C)2005,JPO&NCIPI
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