PURPOSE: To improve strength, impact value, fatigue strength, etc., by subjecting a steel material with the specific ratios of C, Si, Mn, P, S, Al, N, etc., to a vacuum carburization and thereafter applying it to working and quenching in a hot area, etc.

CONSTITUTION: The steel consisting of, by weight, 0.1W0.25% C, ≤0.5% Si, 0.3W1.8% Mn, ≤0.02% P, ≤0.03% S, ≤0.02% Al and ≤0.02% N, and contg. at need, ≤0.3% Cn and/or ≤0.25% Ni, ≤1.25% Cr and/or ≤0.3% Mo with the balance Fe is melted to produce. Said steel material is subjected to the vacuum carburization and is applied to the working and quenching in the hot or warm area.