HIGH TENSILE STRENGTH STEEL EXCELLENT IN STRESS CORROSION CRACKING RESISTANCE AND LOW TEMPERATURE TOUGHNESS AND ITS PRODUCTION

摘要

PROBLEM TO BE SOLVED: To produce an ultrahigh tensile strength steel excellent in stress corrosion cracking resistance and low temp. toughness by forming its structure into a one essentially consisting of a mixed tempered one of acicular and massive martensite and incorporating the carbides of Cr or the like therein. ;SOLUTION: The components of a steel are composed of, by weight, 0.06 to 0.12% C, 0.02 to 0.25% Si, 0.05 to 0.50% Mn, 11.0 to 13% Ni, and the balance iron. Furthermore, one or more kinds among 0.8 to 2.5% Mo, 1.0 to 3% Cr, 0.05 to 0.20% V and 0.01 to 0.10% Al are incorporated therein. Moreover, one or more kinds among Cu, Nb, Ti, Ca and rare earth metals may be incorporated therein. The slab thereof is heated at 1000 to 1250°C and is subjected to hot working at ≥50% reduction of area, the Δ working is finished at ≥700°C, and it is cooled to ≤150°C. After that, it is heated at the Ac₃-40°C to less than the Ac₃, is thereafter quenched and is tempered at less than the Ac₁. Thus, its structure is formed into a mixed tempered one of acicular and massive martensite. In this way, the steel applicable even in a severe using environment can be provided.;COPYRIGHT: (C)1997,JPO