PREPARATION OF HIGHHTENSILE STEEL WITH LOW YIELD RATIO* LOW CARBON AND LOW ALLOY

摘要

PURPOSE:To obtain high tensile low carbon steel with low yield ratio, high strength and high toughness by a method wherein a steel segment comprising a specific composition such as C, Si or the like is rolled under a specific condition and, thereafter heat treatment and annealing are applied in a combined manner. CONSTITUTION:A steel segment comprising C; 0.05-0.25%, Si; 0.01-0.8%, Mn; 0.2-2%, P; below 0.04%, S; below 0.04%, sol. Al; 0.005-0.15%, N; below 0.01%, balance of iron and the like or a steel segment containing moreover one or more of Cu; below (hereinafter same) 1%, N; 2%, Cr; 2%, Mo; 1%, V; 0.2%, Nb; 0.2%, Ti; 0.1%, B; 0.05% is subjected to rolling of cumulative draft above 25% at below 950 deg.C and maintained under heating at a temperature from AC1 point to AC2 point, thereafter cooled at a speed faster than air cooling and, subsequently annealed at a temperature below AC1 point. Thereby, a title high tensile steel which could not been obtained conventionally is obtained.