PURPOSE: To obtain the titled alloy steel having superior machinability, high wear resistance and high dimensional stability by adding specified proportions of C, Si, Mn, P, S, Ni, Mo, and Co to iron.

CONSTITUTION: Alloy steel consisting of by wt% ≤0.02 C, ≤0.10 Si, ≤0.015 S, 12.0W15.0 Ni, 9.0W11.0 Mo, 13.0W15.0 Co, and residual wt% Fe and some impurities, is prepd. Since the alloy steel is softened to about HRC35 by the solution treatment at 950W1,050°C, the cutting is possible. When it is aged for about 3hr thereafter at about 480°C, it is hardened by precipitation to HRC62, and its wear resistance is increased. Further, the alloy steel requires no surface hardening treatment such as nitridation. The dimensional stability is high for the aging treatment. The production is possible by melting in the air because Ti is not contained.