Fatigue and Strain Hardening of Simulated Case Microstructure in Carburized Steels

摘要

Tension, compression, and cyclic stress-strain testing were used to evaluate the effect of retained austenite on high and low cycle fatigue of Cr-Mo-Ni alloy steels containing 0.8 pct C to simulate the high carbon case of carburized steels. In low cycle fatigue, cracks develop at austenite grain boundaries early during tensile and cyclic loading. Propagation of these cracks is stabilized in specimens which contain large amounts of retained austenite which dynamically forms martensite by strain-induced transformation. Without sufficient austenite, incipient cracks are not effectively stabilized, and low cycle fatigue life is reduced. In high cycle fatigue, insufficient strain accumulates for the activation of strain-induced martensite, and large amounts of retained austenite are not as beneficial as in low cycle fatigue. Microstructures with 30--35 volume percent retained austenite and fine mixtures of martensite and austenite which contribute to high elastic limits appear to be the most satisfactory for good high and low cycle fatigue resistance. 18 refs., 6 figs., 4 tabs. (ERA citation 13:051616)