PURPOSE: To obtain the titled steel having ≥60kgf/mm2 tensile strength and superior toughness, by heating steel having a prescribed component compsn. to a specified high temp. range, rolling at uncrystallized range succeeding to austenite recrystallization range, then forcedly cooling and temper treating.

CONSTITUTION: Steel contg. by weight 0.02W0.15% C, 0.40W0.80% Si, 0.80W1.60% Mn, 0.005W0.10% V, 0.005W0.10% Nb, ≤0.050% Al, ≤0.020% P, ≤0.015% S is treated as follows. Namely, the steel is heated to temp. range of 950W1,200°C, then rolled by ≥30% draft at uncrystallized range succeeding to austenite crystallization range to refine structure of steel. Immediately thereafter, the steel is forcedly cooled to ≤200°C by 5°C/sec rate to finish completely martensite transformation. Next, the steel is tempered at 200W400°C range to obtain the title steel.