Fatigue Failure Analysis of a 42CrMo4 Crankshaft

This study presents a root cause failure analysis of a 42CrMo4 steel crankshaft used in a power generator, which fractured after approximately 11,600 hours (~1.3 years) of service. A comprehensive investigation was conducted using visual inspection, chemical composition analysis, microstructural characterization, hardness testing, scanning electron microscopy (SEM) and fractography. The fracture surface of shaft exhibited beach marks and fatigue striations, confirming fatigue as the dominant failure mechanism. Non-metallic inclusions and metallurgical defects acted as stress concentrators and served as crack initiation sites, facilitating fatigue crack propagation. The final fracture zone showed features of ductile overload in the over load region. These findings indicate that while the alloy met compositional and hardness requirements, inadequate processing and the presence of inclusions detrimentally affected the fatigue response of the alloy. The study underscores the importance of stringent metallurgical quality control to improve the service life and reliability of critical rotating components such as crankshafts