MANUFACTURE OF TEMPERED 80KGF/MM2 CLASS HIGH TENSILE FORCE STEEL SHEET SUPERIOR IN SULFIDE STRESS CORROSION CRACKING RESISTANCE

摘要

PURPOSE:To manufacture the titled steel sheet, by rolling Cr-Mo steel slab having a specified compsn., then heat treating the sheet to a specified temp. to form a suitable decarburized and boron removed surface layer, next applying quenching the tempering treatments thereto. CONSTITUTION:Steel slab consisting of, by weight 0.06-0.14% C, =0.50% Si, 0.30-1.50% Mn, =0.025% P, =0.020% S, =0.50% Cu, 0.30-1.50% Cr, 0.10-0.50% Mo, 0.01-0.10% V, 0.010-0.10% Al, 0.0005-0.0015% B, =0.005% N and the balance Fe with inevitable impurities, further satisfying PCM=0.27% if denoted as PCM=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B% is rolled to a prescribed thickness. Then, the rolled sheet is heated to 1,100-1,300 deg.C, to form decarburized and boron removed layer of =0.05% C, =0.003% B and =0.5mm thickness on steel sheet surface layer, next, quenching tempering treated, to obtain the titled steel sheet.