THERMOMECHANICAL TREATMENT OF HIGH STRENGTH STEEL PRODUCT EXCELLENT IN DELAYED FRACTURE CHARACTERISTIC

摘要

PROBLEM TO BE SOLVED: To provide a thermomechanical treatment process for a high strength steel product having tensile strength higher than 1400 MPa and excellent in delayed fracture characteristic. ;SOLUTION: A steel, which has a composition consisting of, by weight, 0.25-0.35% C, ≤0.5% Si, 0.2-1% Mn, ≤0.01% P, ≤0.01% S, 0.01-0.1% Al, 0.002-0.01% N, 7-12% Ni, and the balance Fe with inevitable impurities and also has a martensitic structure or a tempered martensitic structure, is used. The steel is worked in the temperature region between the Ac1 and the Ac3 point at 30-80% reduction of area, reheated to a temperature between the Ac1 and the Ac3 point, and then cooled without delay.;COPYRIGHT: (C)2000,JPO