Macropitting in Microsegregated Induction-Hardened Gear Tooth

Abstract

A sample from a large gear was submitted for investigation into the cause of apparent macropitting observed around the pitch line on the loaded face of one of the teeth. A banded (light and dark etching) martensitic structure was observed, which varied significantly in hardness. Cracking was observed to be isolated to the case-hardened surface. The macropitting observed appeared to be consistent with contact fatigue. The nonhomogeneous microstructure observed may have been particularly susceptible to fatigue initiation and propagation. The microstructure observed appeared to be due to a lack of homogenous diffusion of carbon during the austenization of the part from the annealed condition.