Microstructure mastering and fatigue behavior of duplex stainless steel obtained with laser powder bed fusion

Microstructure and mechanical behavior of duplex stainless steels (DSS) are well known when elaborated with conventional processes. Nowadays, many studies aimed to characterize this material for additive manufacturing (AM) processes like laser powder bed fusion (LPBF) [1], [2]. The as-built LPBF microstructure of this alloy is totally ferritic [1]. Heat treatments are therefore necessary to recover the duplex microstructure. These heat treatments need to be optimized. The effects of annealing heat treatments on the microstructure and mechanical behavior of DSS are now known [2], but the consequences on its fatigue strength need to be explored. In this study, firstly, the duplex microstructure will be controlled by heat treatments to obtain austenitic phase with different grain morphology. Then, the influence of microstructure on tensile high cycle fatigue behavior will be investigated. As a result, a microstructure with coarser austenite grains has no effect on fatigue behavior compared to the fully ferritic As-built material whereas the finer microstructure allows an improvement. Even if there is austenite phase improving the material ductility, fatigue damage initiation is always due to pore defects.