Fatigue Behaviour of Metastable and Stable Austenitic Steels

Abstract

An attempt has been made to survey the fatigue behaviour of three different austenitic steels. The materials tested are an Fe-3ONi alloy as metastable austenite, an Fe-38Ni alloy as stable austenite, and an Fe-25Ni-16Cr alloy of low stacking fault energy. It was found that at low stress amplitudes the fatigue life of the metastable steel was longer than that of the stable ones, while at high stress amplitudes the metastable steel was inferior to the stable ones. This is probably attributed to the differences of the rate and period of martensite formation. The fatigue life of the Fe-25Ni-16Cr alloy was less than that of the Fe-38Ni alloy at only high stress amplitude. The Fe-30Ni alloy was cyclically hardened remarkably with martensite formation, but its cyclic strain behaviour except the hardening resulted from the martensite formation was extremely similar to that of the Fe-38Ni alloy, that is, at high stress amplitudes the hardening occured remarkably and at low stress amplitudes softening occured slightly. Fatigue crack propagation properties of the Fe-30Ni alloy was also better than that of the Fe-38Ni alloy at low ΔK level, but at high ΔK level the former was inferior to the latter.