MANUFACTURE OF HIGH TENSILE STEEL MATERIAL HAVING FINE GRAIN STRUCTURE

摘要

PURPOSE:To obtain high tensile steel materials having increased strength and toughness, by shortening heating times in the austenite region of the steel materials whose hardenability is raised by adding B and quenching the steel materials while they are kept in a fine grain state and tempering them for a short time. CONSTITUTION:An ingot of low carbon steel containing 0.07-0.16% C, 0.10- 1.00% Si, 0.50-1.50% Mn, =1.00% Cr, =0.70% Mo, 0.05-0.11% Al, =0.0050% N, 0.0005-0.0030% B, or furthermore one or =2 kinds among 0.10-0.30% Cu, 0.20-1.50% Ni, 0.01-0.06% V is hot-worked, cooled to a temperature below Ar1, heated to the max. heating temperature of Ac3 point -950 deg.C for a short time of =100sec and immediately quenched while austenite grains are kept a fine state. This ingot is tempered under conditions in which a tempering constant TP=(T+ 273)(20+logt), (T: temp. deg.C, t: time hr) becomes =18,000. The high tensile steel both superior in strength and toughness can be obtained.