MANUFACTURING METHOD OF STEEL SHEET FOR HIGH STRENGTH HIGH TOUGHNESS STEEL PIPE AND STEEL SHEET FOR HIGH STRENGTH HIGH TOUGHNESS STEEL PIPE

摘要

PROBLEM TO BE SOLVED: To provide a steel sheet for high strength high toughness steel pipe achieving low YR without adverse effect on absorption energy and a manufacturing method thereof.SOLUTION: There is provided a manufacturing method of a steel sheet for high strength high toughness steel pipe with a high deformability including heating a steel raw material having a specific component composition at surface temperature:1000°C to 1250°C, first rolling it in a recrystallization temperature range, a second rolling it under a condition with cumulative draft of 40% to 75% in a non-recrystallization range of 900°C or less after the first rolling and accelerating cooling under following cooling initiation temperature and cooling stop temperature after the second rolling. Cooling initiation temperature:(Ar-50°C) or more and less than Ar. Cooling stop temperature:250 to 500°C.SELECTED DRAWING: None