Abstract: A steel material of 85 to 95 HRB exhibiting a ratio of area occupied by ferrite of 30% or higher, which steel material comprises given amounts of C, Si, Mn, S, Ti, Cr, Al and B and the balance of iron and unavoidable impurities, is subjected to induction hardening. After the hardening, the surface of the steel material exhibits an Hv value of 640 to 730. When t refers to the effective hardening depth, namely, the distance from the surface to a region exhibiting an Hv value of 392 and r refers to the radius of the steel material, the hardened layer ratio, t/r, is 0.4 or higher.

Abstract: Disclosed is a production process that can suppress the formation of large-diameter TiN or N-rich TiCN inclusions which adversely affect machinability and consequently can produce a cast steel billet or steel ingot or a steel material of a Ti-added case hardening steel having excellent machinability. The production process comprises the step of casting a steel comprising by weight carbon (C): 0.10 to 0.30%, titanium (Ti): 0.05 to 0.20%, and nitrogen (N): not more than 0.0100% into a round cast steel billet or steel ingot having a diameter of not more than 23 cm or, in the alternative, a rectangular cast steel billet or steel ingot having a short side length of not more than 23 cm.