HIGH-STRENGTH STEEL FOR WELDED STRUCTURE HAVING EXCELLENT ULTRAHIGH HEAT INPUT WELD PART HAZ TOUGHNESS, AND ITS PRODUCTION METHOD

摘要

PROBLEM TO BE SOLVED: To provide steel for high strength welded structure which has excellent toughness in an ultrahigh heat input weld part HAZ (heat affected zone), and to provide its production method.;SOLUTION: The high strength steel for welded structure having the excellent toughness in the ultrahigh heat input weld part HAZ has a composition comprising, by mass%, 0.01 to 0.20% C, 0.02 to 0.50% Si, 1.5 to 3.5% Mn, ≤0.03% P, 0.005 to 0.030% S, 0.005 to 0.50% V, 0.005 to 0.20% Nb, 0.003 to 0.050% Al, and 0.003 to 0.050% Ti, and further simultaneously comprising ≥0.0001% Mg and Ca respectively, and in which the total lies in the range of 0.0010 to 0.010%, and the balance iron with inevitable impurities, and the content of the Mg has the relation expressed by formula {free [Mg]=total [Mg]-[Mg] contained in the total oxide≥1 ppm}.;COPYRIGHT: (C)2008,JPO&INPIT