PURPOSE: To provide a titled tough and hard steel having an improved cold forging characteristic by specifying the compsn. of a high carbon steel which contains Si and Mn up to the decreased upper limit, contains P, N and O in less amt. and contains S, Al and Cr.
CONSTITUTION: A tough and hard steel for cold forging contains 0.40W0.65wt% C, 0.01W0.05% Si, 0.20W0.40% Mn, 0.02W0.03% S, >0.01 and ≤0.04% Al and 0.3W0.8% Cr and is limited to ≤0.01% P, ≤0.005% N and ≤0.005% O. Said steel is a carbon steel for machine structural use having improved cold forgeability. The above-mentioned component compsn. is limited to contain essentially P, N and O among Si, Mn, P, N and O which affect adversely deformation resistance, at a low rate, to decrease the upper limit of Si and Mn and to make up the hardenability to be correspondingly deteriorated with C and Cr to improve the cold forgeability. The deformation resistance is thus remarkably improved.
INOUE HISASHI
TANABE KOUJI
KOSEKI TADASHI
