490MPa CLASS HIGH TENSILE STEEL FOR WELDED STRUCTURE HAVING EXCELLENT HIGH TEMPERATURE STRENGTH AND

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PROBLEM TO BE SOLVED : To provide a high tensile steel for a welded structure having high temperature strength in the temperature range of 600 to 800°C, and to provide its production method. SOLUTION : The 490 MPa class high tensile steel for a welded structure having excellent high temperature strength has a composition comprising 0.005 to <0.040% C, ≤0.5% Si, ≤0.5% Mn, ≤0.02% P, ≤0.01% S, 0.3 to 1.5% Mo, 0.03 to 1.5% Nb, ≤0.06% Al and ≤0.006% N, and, if required, comprising Cu, Ni, Cr, V, Ti, Ca, rare earth metals and Mg, and whose weld cracking parameter defined as PCM=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20/Mo/15+V/10+5B is ≤0.15%, substantially comprising no B, and the balance iron with inevitable impurities, and has a microstructure essentially consisting of a mixed structure of ferrite and bainite, and in which the fraction of the bainite is 20 to 90%. COPYRIGHT : (C)2006, JPO&NCIPI