| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel material for heavy heat input welding which exhibits excellent toughness in a welding-heat-affected zone, even when subjected to heavy heat input welding with a welding heat input of more than 300 kJ/cm.SOLUTION: A steel material for heavy heat input welding comprises, by mass%, prescribed amounts of C, Si, Mn, P, S, Al and Nb, 0.004-0.030% Ti, 0.0003-0.0030% B, 0.0035-0.0070% N, 0.0005-0.0030% Ca, ≤0.0040% O and, if required, at least one of V, Ni, Cu, Cr, Mo, W, Mg, Zr and REM, and the balance being Fe and unavoidable impurities, while satisfying following relation (1): 0<(Ca-(0.18+130×Ca)×O)/1.25/S≤0.8, wherein Ca, O and S represent the contents (mass%). When the steel material for heavy heat input welding is subjected to heavy heat input welding with a welding heat input of >300 kJ/cm, the area fraction of island martensite is ≤1% in a structure of a welding-heat-affected zone in the vicinity of a bond. |
