Fatigue properties of carburized alloy steel in very high cycle regime under torsional loading

A very high cycle fatigue diagram and crack propagation behavior of carburized SCM420H are obtained using an ultrasonic torsional fatigue testing machine and are compared with those of non-carburized SCM420H. Fatigue crack initiation and growth are observed in the very high cycle regime for both carburized and non-carburized SCM420H. Results show that carburizing of SCM420H is effective for fatigue life enhancement in the very high cycle regime. Furthermore, crack deflection from mode II to mode I occurs under torsional fatigue. This behavior is discussed based on fracture mechanics.