| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for stably and efficiently manufacturing a super high-strength steel sheet with an adequate shape. SOLUTION: This steel sheet comprises, by mass, 0.03-0.25% C, 2% or less Si, 1-3.5% Mn, 0.08% or less P, 0.01% or less S, and the balance being substantially Fe. The manufacturing method includes, when manufacturing the super high-strength steel sheet by hot-rolling, pickling or further cold-rolling the steel having the above composition, and subsequently annealing/tempering and temper-rolling it, performing the annealing/tempering step according to the following steps (1) to (4): (1) soaking the cold-rolled sheet at an Ac1 transformation temperature or higher; (2) quenching it at a cooling rate of 100°C/s or higher (preferably 300°C/s or higher) from a quenching start temperature to 200°C or lower; (3) rapid-heating it at a heating rate of 10°C/s or higher, to a temperature of (quenching stop temperature + 100)°C or higher; and (4) tempering it at 200 to 500°C. COPYRIGHT: (C)2005,JPO&NCIPI
|
