METHOD FOR PRODUCING THICK HIGH STRENGTH STEEL PLATE HAVING EXCELLENT TOUGHNESS, AND THICK HIGH STRENGTH STEEL PLATE HAVING EXCELLENT TOUGHNESS

摘要

PROBLEM TO BE SOLVED: To simultaneously satisfy a sheet thickness of 50 to 80 mm, a yield strength in a class of 390 to 460 MPa, toughness in the central part of the sheet thickness, high heat input weld HAZ (Heat Affected Zone) toughness and high rolling efficiency.;SOLUTION: A continuously cast slab having a composition in which the contents of C, Si, Mn, P, S, Al, Ti, N and O are controlled to prescribed ranges, the content of B is controlled to 0.0003 to 0.003%, the content of Mo is controlled to 0.01 to 0.2%, one or more selected from Ca and Mg are comprised, an effective B content obtained by prescribed formula is controlled to ≥0.0003%, a carbon equivalent Ceq is controlled to 0.30 to 0.40%, and the balance iron is cooled to Ar₃-200°C, is thereafter reheated at 1,000 to 1,250°C, is hot-rolled so as to be finished at 800 to 900°C, and is successively subjected to accelerated cooling from Ar₃ or higher.;COPYRIGHT: (C)2007,JPO&INPIT