| 摘要 |
PURPOSE:To produce a high tensile steel having high strength, high toughness and excellent weldability by subjecting successively a steel having a specific compsn. and sensitivity index for weld crack to hot rolling, reheating, hardening and tempering under specific conditions. CONSTITUTION:A steel contg., by weight, 0.07-0.15% C, 0.05-0.35% Si, 0.40- 1.60% Mn, 0.40-1.00% Cr, 1.30-3.50% Ni, 0.40-0.80% Mo, 0.01-0.06% V, 0.005-0.030% Nb, <=0.0020% B, <=0.50% Cu, 0.02-0.10% solAl, <0.0040% N and the balance Fe and unavoidable impurities, and having <=0.31(%) PCM (sensitivity index for weld crack) expressed by the formula is heated to >=1,050 deg.C and is hot rolled. The hot rolled steel is then reheated to a temp. region of the Ac3 transformation point -1,050 deg.C and thereafter the steel is hardened from said temp. and is tempered at the Ac1 transformation temp. or below. The steel having about >=90kgf/mm.<2> yield point, about >=97kgf/mm.<2> tensile strength and about <=-60 deg.C transition temp. of the shock-broken surface is thus obtd. |
