METHOD FOR PRODUCING STEEL SHEET FOR HIGH STRENGTH STEAM PIPING HAVING EXCELLENT WELD HEAT AFFECTED

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PROBLEM TO BE SOLVED : To provide a method for producing a steel sheet having excellent weld heat affected zone toughness which has a yield strength of ≥550 MPa in a medium temperature region, and is suitable for a high strength welded steel pipe for steam piping. SOLUTION : A steel having a composition comprising, by mass, 0.05 to 0.09% C, 0.05 to 0.20% Si, 1.5 to 2.0% Mn, ≤0.020% P, ≤0.002% S, 0.05 to 0.3% Mo, 0.005 to 0.05% Nb, 0.005 to 0.02% Ti and 0.01 to 0.04% Al, satisfying Ti/N of 2.0 to 4.0, and, if required, comprising one or more kinds selected from Cu, Ni, Cr, V, Ca and rare earth metals, and the balance Fe with inevitable impurities is heated at 1, 000 to 1, 200°C, is thereafter hot-rolled at a cumulative draft of ≥50% in ≤900°C and also at a rolling finishing temperature of ≤850°C, and is subsequently subjected to accelerated cooling to 400 to 550°C at a cooling rate of ≥5°C/s. COPYRIGHT : (C)2006, JPO&NCIPI