| 摘要 |
PROBLEM TO BE SOLVED: To provide a production method of a steel sheet for high-tension linepipes which, when used for linepipes, exhibits suitable strengths, suitable toughness, suitable DWTT properties, and excellent CTOD properties. SOLUTION: The production method comprises heating a steel having specified components and containing the balance comprising Fe and unavoidable impurities to 1,000 to 1,200°C, hot-rolling the steel at a final rolling temperature equal to or higher than the Ar<SB>3</SB>transformation point, or desirably hot-rolling the steel in an austenite unrecrystallization temperature region at a cumulative pressure reduction rate of 50% or larger, cooling the steel from the temperature region equal to or higher than the Ar<SB>3</SB>transformation point to a quenching cooling termination temperature ranging from 300°C to the initial martensite transformation temperature (Ms point) at a cooling speed equal to or higher than the martensite formation critical cooling speed Vcrm, keeping the steel at a temperature within the cooling termination temperature±50°C for 1 to 100 s after the cooling termination, and cooling the steel in air to room temperature or immediately heating the steel rapidly from the temperature to a temperature region ranging from 450°C to the Ac<SB>1</SB>transformation point at a speed of temperature rise of 1°C/s or higher. COPYRIGHT: (C)2007,JPO&INPIT
|
