Bending Fatigue of Carburized Steels

Bending fatigue of carburized steel components is a result of cyclic mechanical loading. This article reviews the alloying and processing factors that influence the microstructures and bending fatigue performance of carburized steels. These include austenitic grain size, surface oxidation, retained austenite, subzero cooling, residual stresses, and shot peening. The article describes the analysis of bending fatigue behavior of the steels based on S-N curves that represents a stress-based approach to fatigue. It discusses the types of specimen used to evaluate bending fatigue in carburized steels. The stages of fatigue and fracture of the steels, namely crack initiation, stable crack propagation, and unstable crack propagation, are reviewed. The article analyzes the intergranular fracture at the prior-austenite grain boundaries of high-carbon case microstructures that dominates bending fatigue crack initiation and unstable crack propagation of direct-quenched carburized steels.