Effect of microstructure on fatigue crack propagation behavior of multiphase advanced high strength steels

Abstract The influence of microstructural characteristics on the fatigue crack propagation behavior of multiphase advanced high strength steels (AHSSs) was investigated in the present study with a particular focus on the retained austenite. The steel samples with unified chemical composition were treated by various processes to obtain press-hardened (PH), dual-phase (DP), quenching and partitioning (QP), and transformation-induced plasticity (TRIP) AHSSs. The results demonstrate that an increased proportion of retained austenite correlate with the enhanced tensile elongation and a reduced fatigue crack propagation rate in these AHSSs. This effect is attributed to the retardation of fracture propagation, which occurs as result of the transformation of austenite into martensite. Furthermore, the study reveals that retained austenite with a fine block morphology and high average boundary angles contributes to sustained resistance to fatigue crack propagation. It is believed that this resistance is attributed to the deflection of crack growth through the fracture along irregular and densely distributed block boundaries.