On the high cycle fatigue behavior of duplex stainless steels: Influence of thermal aging

In this investigation the high cycle fatigue (HCF) behavior of an austenite-ferrite duplex stainless steel (DSS) is studied as a function of aging at 475 °C. It is found that the HCF strength and the fatigue sensitivity of DSS increase with aging. The fatigue strength improvement results from the higher cyclic yield stress of the spinodally-hardened ferrite which induces an increasing difficulty for early propagation, into and through the ferritic matrix, of microcracks nucleated within austenite. The fatigue sensitivity impairment is suggested to be correlated to an easier microcrack nucleation stage in the aged DSS as compared to the annealed or unaged one.