STEEL SHEET FOR ULTRAHIGH HEAT INPUT WELDING

PROBLEM TO BE SOLVED : To provide a steel sheet for an ultrahigh heat input welding in which the toughness of the weld zone is not reduced even if ultrahigh heat input welding in which heat input exceeds 800 kJ/cm is performed. SOLUTION : The steel sheet for ultrahigh heat input welding has a composition comprising, by mass, 0.001 to 0.15% C, 0.05 to 0.8% Si, ≤0.01% Al, 0.5 to 2.0% Mn, 0.0005 to 0.0100% O, 0.0005 to 0.0100% S and 0.0010 to 0.0100% rare earth metals, and in which the content of O, the content of Mn and the content of rare earth metals satisfy the following relationship (1), and the content of S and the content of Mn satisfy the following inequality (2), and the balance iron with inevitable impurities : the inequality (1) is expressed by [Mn]×[O]×0.2≤[REM]≤[Mn]×[O]×1.2, and the inequality (2) is expressed by [S]≥0.00294/[Mn].