| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength thick steel plate whose weldability is excellent and having a yield stress YS of≥650 MPa and a yield ratio YR of≤80%, and to provide its production method. SOLUTION: A steel slab in which the componential composition of a base metal is made proper is heated at 1,000 to 1,250°C, is thereafter subjected to hot rolling in which rolling finishing temperature is≥800°C, and is subjected to accelerated cooling from the temperature range of an Ar<SB>3</SB>transformation point or above to the temperature range of≤350°C at a cooling rate of 5 to 60°C/s, and the cooling is temporarily interrupted. Thereafter, the steel is reheated to a temperature of 350 to 550°C at a temperature rising rate of≥2°C/s, is held to the temperature for≤15 min, and is then cooled, so as to obtain the high strength thick steel plate in which the area fraction of a martensitic phase in the region of≥90% in the cross-section of the plate thickness is≥60%, and the balance bainitic phase. COPYRIGHT: (C)2008,JPO&INPIT
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