| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel sheet for high strength line pipe which is excellent in resistance to crack induced with hydrogen and has small reduction in yield stress in the steel pipe peripheral direction after forming into the steel pipe from the yield stress of the steel sheet before forming into the steel pipe by a Bauschinger effect. SOLUTION: This steel sheet contains, by mass, 0.03-0.06% C, 0.01-0.5% Si, 0.8-1.5% Mn,≤0.08% Al, 0.0010-0.0050% Cu,≤0.0030% O and if necessary, one or more elements of Mo, Ti, Nb, v, Cu, Ni, Cr, B, Mg, REM and the balance Fe with inevitable impurities, and Ca,V and S satisfies the following formula, wherein the volume partial ratio of a second phase tissue in the structure is≤3% and the hardness difference between the surface layer and the sheet thickness center part is within HV40. The formula is 1.0%≤(1-130×[O])×[Ca]/(1.25×[S])≤4.5. The above steel is acceleratively cooled after hot-rolling and reheated, and the temperature difference between the steel sheet surface and the sheet thickness center part is set to≥20°C. COPYRIGHT: (C)2008,JPO&INPIT
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