THERMOMECHANICAL TREAETMENT OF HIGH STRENGTH STEEL EXCELLENT IN DELAYED FRACTURE CHARACTERISTIC

摘要

PROBLEM TO BE SOLVED: To provide a method for producing high strength steel member having ≥1400 Pa tensile strength and excellent in delayed fracture characteristics. ;SOLUTION: A steel has chemical components contg., by weight, 0.25 to 0.35% C, ≤0.5% Si, 0.2 to 1.0% Mn, ≤0.01% P, ≤0.01% S, 0.01 to 0.1% Al, 0.002 to 0.01% N, 7 to 12% Ni, and the balance Fe with inevitable impurities. The steel having a martensitic structure or a tempered martensitic structure is worked by 30 to 80% reduction of area at ≤600°C, is successively heated at the AC3 point to 900°C without cooling and is immediately cooled, or, after cooling, it is reheated at the AC3 point to 900°C and is immediately cooled.;COPYRIGHT: (C)1999,JPO