| 摘要 |
PROBLEM TO BE SOLVED: To provide a method of producing a high tensile steel sheet which has a tensile strength of 1,180 MPa or more and is more excellent in weldability and delayed fracture resistance than conventional steel materials.SOLUTION: There is provided a production method which comprises: heating a steel to Actransformation temperature or more, the steel containing, by mass%, C of 0.10 to 0.20%, Si of 0.01 to 0.6%, Mn of 0.5 to 2%, P of 0.02% or less, S of 0.003% or les, Al of 0.005 to 0.1%, N of 0.0005 to 0.008% and the balance of Fe with inevitable impurities and having a carbon equivalent Ceq of 0.60 or less and a weld crack sensitivity index Pcm of 0.30% or less; hot-rolling the heated steel sheet with a cumulative rolling reduction at a non-recrystallization temperature range of 30% or more; finishing the hot-rolling at Actransformation temperature or more; cooling down the hot-rolled steel sheet from Actransformation temperature or more to a temperature of 250°C or less at a cooling rate of 10°C/s or more; and performing tempering treatment on the cooled steel sheet in such a way that the cooled steel sheet is reheated at an average temperature raising rate of 1°C/s or more to the highest end-point temperature in the range of 100 to 400°C. |
