Improvement on the Fatigue Strength of Case Hardened Gears by a New Heat Treatment Process

It has been well-known that retained austenite in the surface of carburized or carbonitrided steel improves the pitting resistance of the steel under rolling contact, although some deteriorative effect on the bending fatigue has also been reported.

The aim of this study is to make clear the influence of retained austenite content on the pitting and on the bending fatigue, and also to develop a heat treating process which enables quantitative control of retained austenite on the surface of gears.

The gears treated by the newly developed carbonitriding process to contain 60–70% retained austenite in the surface achieved a pitting life almost three times longer than those subjected to conventional carburizing without any bending fatigue failure.