HIGH STRENGTH STEEL EXCELLENT IN TOUGHNESS IN HIGH HEAT INPUT WELD HEAT-AFFECTED ZONE

摘要

PROBLEM TO BE SOLVED: To provide a high strength steel which is excellent in toughness in a weld heat-affected zone even for high heat input welding having a welding heat input of 300 kJ/cm and which has a sheet thickness of ≥40 mm and a yield strength of 460 N/mm².;SOLUTION: The steel has a steel composition containing, by mass, 0.03 to 0.09% C, 0.02 to 0.15% Si, 1.5 to 2.5% Mn, 0.005 to 0.06% Al, ≤0.015% P, 0.0005 to 0.0050% S, 0.005 to 0.025% Nb, 0.005 to 0.02% Ti, 0.0040 to 0.0070% N, 0.0005 to 0.0030% Ca, 0.0005 to 0.0025% B and 0.38 to 0.45% Ceq (IIW), and if required, further containing one or more selected from among V, Ni, Cu, Cr, Mo and W, and the balance Fe with inevitable impurities, and the steel contains 50 to 1,000 pieces/mm² of acid sulfide grains having a diameter of the equivalent circle of 0.5 to 3 μm and containing at least Ca, Al, Mn, O and S and elements other than O in specified quantity.;COPYRIGHT: (C)2011,JPO&INPIT