| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for producing a high workability and extra-high strength cold-rolled steel sheet excellent in delayed fracture resistant characteristic after forming. SOLUTION: After casting a steel slab composed of, by mass%, 0.1-0.2% C, 0.01-1.8% Si, 1-2.5% Mn, 0.001-0.05% P, 0.0001-0.005% S, 0.005-0.05% Al, 0.0001-0.005% N and the balance substantial Fe, this steel slab is immediately or once cooled, and after heating, hot-rolling and pickling, the steel sheet obtained by performing the cold-rolling is heated and annealed at 700-900°C and cooled at≥10°C/sec cooling speed and heated so as to rise the temperature at≥10°C/sec heating speed to≥(0.3×heat treatment temperature)°C with an induction-heating and the heat treatment is applied at 150-500°C. COPYRIGHT: (C)2005,JPO&NCIPI
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