THICK STEEL PLATE FOR SHIP, MARINE STRUCTURE AND HYDRAULIC STEEL PIPE HAVING EXCELLENT BRITTLE CRACK ARREST PROPERTIES, AND METHOD FOR PRODUCING SAME

摘要

PROBLEM TO BE SOLVED: To propose a thick steel plate having a plate thickness of 100 mm or less, which has high strength and excellent brittle crack arrest properties without being added with a large amount of Ni, and to provide a method for producing the thick steel plate.;SOLUTION: The method for producing a thick steel plate is provide that comprises: hot rolling a slab containing, in mass%, C: 0.05 to 0.15%, Si: 0.05 to 0.60%, and Mn: 0.8 to 1.8% and, further, containing any one or more of Cu: 0.50% or less, Ni: 1.50% or less, Cr: 0.50% or less, Mo: 0.40% or less, V: 0.07% or less, and B: 0.0003 to 0.0020%, and having a C equivalent of 0.36 to 0.55; reheating the hot rolled steel plate to a temperature of Ac₃ transformation point to (Ac₃ transformation point+70°C); hardening the reheated steel plate to adjust tensile strength to 850 to 1100 MPa; and subjecting the hardened steel plate to a tempering treatment at 550 to 700°C. The thus obtained steel plate has a microstructure at a quarter of the plate thickness including tempering lower bainite and tempering martensite structures, a tensile strength of 570 to 720 MPa, and a T_NDT of -55°C or less in an NRL drop weight test.;COPYRIGHT: (C)2015,JPO&INPIT