摘要 |
PROBLEM TO BE SOLVED: To provide a new low alloy, high strength steel sheet having both of the high strength and good workability, and a producing method therefor. SOLUTION: After annealing a rolled steel having specific chemical compositions to the temperature range of A1 to (Ac3+20)°C, this steel sheet is slowly cooled to the temperature range of A1 to (A1-100)°C at a cooling rate of≤10°C/sec and successively, and after rapidly cooling to near 500°C at a rate of≥60°C/sec, successively, this steel sheet is cooled to≤250°C at a cooling rate of 10 to 30°C/sec without keeping it at near 400°C, and thus, the high strength and excellent ductility with the low alloy composition at the same level as a composite structural steel sheet can be imparted to the steel sheet at the same time. COPYRIGHT: (C)2009,JPO&INPIT
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