GEAR MADE OF STEEL HAVING EXCELLENT CASE CRUSHING RESISTANCE AND REDUCED HEAT TREATMENT STRAIN, METHOD FOR PRODUCING THE SAME, AND STEEL FOR GEAR

摘要

PPROBLEM TO BE SOLVED: To provide a gear having reduced heat treatment strain upon surface hardening treatment by carbonitriding, and exhibiting excellent characteristics in strength essentially required as the one for a gear, particularly, to the fracture stripping damage (generally called as case crushing) of the surface layer part in the gear as the excellent dimensional precision of gear parts is secured. PSOLUTION: In the gear made of a steel having excellent case crushing resistance and reduced heat treatment strain, surface hardness is 650 to 750 Hv, the depth of an effective hardened layer is 0.1 to 0.3 mm, the ferrite fraction of a noncarbonitrided part (core part) is 40 to 80%, and the hardness of the noncarbonitrided part (core part) is 190 to 350 Hv. The steel for a gear is useful for producing the same. PCOPYRIGHT: (C)2007,JPO&INPIT