PROBLEM TO BE SOLVED: To provide a steel material which is used for high heat input welding by a heat input of 20 to 100 kJ/mm, and has high toughness at the HAZ.;SOLUTION: This steel material comprises, by mass%, 0.03-0.17% C, 0.01-0.50% Si, 0.40-1.90% Mn, 0.020% or less P, 0.0010-0.020% S, 0.001-0.070% Al, 0.005-0.030% Ti, 0.0010-0.0100% N, 0.0002-0.0050% B and the balance Fe with unavoidable impurities, so that the expressions of carbon equivalent Ceq=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15 and the amount of solid solution B: EB=B-0.69×N+0.12×Ti can respectively satisfy 0.30≤Ceq≤0.35 and 0.0002≤EB≤0.0010; and has a structure in which intergranular ferrite shares 1 to 20%.;COPYRIGHT: (C)2006,JPO&NCIPI
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