PREPARATION OF UNNORMALIZED HIGH TENSILE STEEL EXCELLENT IN WELDABILITY

摘要

PURPOSE:To prepare unnormalized high tensile steel excellent in weldability at low cost, by applying rolling and heat treatment to a low carbon steel piece under a specific condition. CONSTITUTION:In a steel containing basic components comprising 0.005-0.15% C, 0.1-0.5% Si, 0.8-2.0% Mn, 0.005-0.08% Al, less than 0.008% S and the remainder Fe, at least one of 0.01-0.10% V, less than 0.5% Cu, less than 0.5% Cr, less than 0.5% Mo, 0.002-0.010% Ca, and 0.005-0.010% REM is contained according to necessity to form a slab which is, in turn, heated to a temp. range from an Ar3-point + 70 deg.C to an Ar3-point. The treated steel is subjected to hot rolling under a draft of at least 30% in the non-recrystallized gamma-region thereof and succeedingly cooled to 500 deg.C or less at a cooling speed of 2-40 deg.C/sec in an accelerated state and, after light rolling is again applied to the cooled steel at a temp. of 200 deg.C or more under a draft of 0.5-10%, the resulting steel is cooled in air or allowed to cool gradually. By this method, unnormalized high tensile steel low in carbon content, having high yield strength and excellent in weldability can be prepared at low cost.