PRODUCTION OF MIDDLE-CARBON LOW-ALLOY TOUGH STEEL

摘要

PURPOSE:To produce a middle-carbon low-alloy steel product having high strength and high toughness by subjecting a middle-carbon low-alloy steel ingot having a specific compsn. to hot working, then subjecting the same to a heat treatment under specific conditions. CONSTITUTION:The ingot of the middle-carbon low-alloy steel contg., by weight %, 0.30-0.60% C, 0.01-1.00% Si, 0.10-1.50% Mn, 0.20-4.00% Ni, 0.50-1.50% Cr, 0.50-1.50% Mo, and 0.03-0.30% V is hot rolled and is worked to a steel sheet. This hot rolled steel sheet is heated to =1000 deg.C to austenitize the structure and thereafter, the steel is cooled at, for example, 200 deg.C/min cooling rate to convert the structure to martensite. After the steel sheet is hardened from the Ac3 point-(Ac3 point+130 deg.C) temp. range of this steel in succession thereto, the steel sheet is subjected to a tempering treatment for 4 hours at, prescribed 550 deg.C. The middle-carbon low-alloy tough steel product having =160kgf/mm2 tensile strength and excellent toughness is obtd.