PURPOSE: To manufacture a steel with specified yield strength or offset yield stress strength and superior resistance to sulfide stress corrosion cracking by subjecting a steel contg. specified percentages of C, Si, Mn, V, Al, B and Ni to heating, cooling and tempering under specified conditions.
CONSTITUTION: A steel consisting of 0.05W0.40% C, 0.3W1.5% Si, 0.3W1.0% Mn, 0.05W0.15% V, 0.04W0.1% Al, 0.0005W0.005% B, ≤0.005% Ni and the balance Fe with inevitable impurities or further contg. one or more among ≤1.5% Cr, ≤0.5% Mo, ≤0.5% Cu and ≤0.1% Nb is heated to a temp. above the Ac3 point and cooled at ≥[5÷Ceq(%)]°C/sec cooling rate from 800°C to 500°C to carry out hardening. The hardened steel is tempered at a temp. below the Ac1 point. Thus, a steel with ≥55kgf/mm2 yield strength or offset yield stress strength at 0.2% permanent set and superior SSCC resistance is obtd.
YAMANE YASUYOSHI
TAKADA ISAO
OOTSUBO HIROSHI
