| 摘要 |
PROBLEM TO BE SOLVED: To provide a thick and high tensile strength steel sheet excellent in strength and toughness of a base material and also excellent in toughness of a weld heat-affected zone, and an advantageous method for producing the same.SOLUTION: A thick and high tensile strength steel sheet excellent in toughness of a base material and of a weld heat-affected zone upon multi-layer welding has a chemical component including a basic chemical component of 0.005-0.05% of C, 0.05-0.3% of Si, 0.5-5% of Mn, 0.015% or less of P, 0.005% or less of S, 3% or less of Cr, 5% or less of Ni, 0.005-0.02% of Ti, 0.02-0.04% of Al, 0.007% or less of N, 0.0003-0.003% of B, and 0.0005-0.0030% of O, with the balance comprising Fe and unavoidable impurities, and also satisfies relations: Ceq≥0.65% and Pc≥5.5, when Ceqand Pc are defined by formula (1) and formula (2). In the production method, hot rolling with cumulative draft of at least 50% is performed, and then quenching and tempering treatment is performed. |
