Investigations on the Tooth Root and Pitting Load Carrying Capacity of Case-Hardened Gears with Higher Amounts of Retained Austenite

Abstract Case hardening is the dominant heat treatment process for modern gear applications due to decades of continuous development. It is used to produce a hard and wear-resistant surface layer while maintaining a ductile core structure. In conventionally case-hardened components, the surface layer consists mainly of martensite and a remaining proportion of retained austenite as well as some possible precipitates. It is known from previous studies that surface layer structures with higher amounts of retained austenite can exhibit load carrying capacity potentials compared to conventionally case-hardened gears. However, these tend to form precipitations due to the higher carbon content during the carburization process. The experimental investigations carried out on gears confirmed that surface layer conditions with finely distributed precipitations in particular have a positive influence on the tooth root and tooth flank load carrying capacity of case-hardened gears. Endurance tests on the tooth root load carrying capacity of conditions with high amounts of retained austenite led to significantly increased strength values compared to the conventionally case-hardened condition. With regard to massive network-like carbide precipitations, a negative influence has tended to emerge, but this can be compensated for by appropriate blasting treatment of the gears.