Fatigue properties of two case hardening steels after carburization

Fatigue properties of two case hardening steels after carburization have been investigated by means of rotating bending fatigue tests and rolling contact fatigue tests. Results show that the steel with higher Al and N contents has higher rotating bending fatigue limit and rolling contact fatigue limit, increasing from 865 to 950 MPa and from 3575 to 3725 MPa, respectively. It is also shown that the steel with higher Al and N contents has finer prior austenite grain sizes and higher hardness in the carburized case. Scanning electron micrographic observations on the fractured surface of specimens for rotating bending fatigue tests show that fatigue crack usually initiated from oxide inclusions and propagated along prior austenite grain boundaries, indicating that the finer grain size and higher hardness in the carburized case of the steel with higher Al and N contents can contribute to its higher fatigue properties.