Effect of tempering temperatures on the fatigue behavior of 0.6% C martensitic steel

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The martensitic steels have attracted significant attention in various industries due to their superior mechanical properties and fatigue resistance. However, the fatigue behavior of high-carbon martensitic steels remains insufficiently understood. In this study, the effect of tempering process on the fatigue behavior of a 0.6% C martensitic steel was systematically investigated. Three tempering conditions, namely T180, T500 and T650, were applied, resulting in distinct microstructures and mechanical responses. The fatigue performance was elucidated through a combination of crystal plasticity finite element method (CPFEM) and experimental characterization. The results indicate that tempering has a limited effect on grain size while enhanced carbon segregation promotes the formation of dense carbides along boundaries. Carbides and inclusions serve as the primary crack initiation sites regardless of tempering condition, whereas intergranular crack propagation is more pronounced in the low-tempered state. Combined CPFEM and experimental analyses reveal that fracture toughness, governing the main crack formation, plays a critical role in controlling fatigue resistance. Increased fracture toughness at higher tempering temperatures significantly delays the cycles to the main crack formation. However, excessive tempering leads to substantial strength degradation, which increased the potential number of main crack formation sites and deteriorates fatigue resistance.