Effect of annealing and strain rate on the microstructure and mechanical properties of austenitic stainless steel 316L manufactured by selective laser melting

New insights are proposed regarding the α′-martensite transformation and strengthening mechanisms of austenitic stainless steel 316L fabricated using selective laser melting (SLM-ed 316L SS). This study investigates the effects of annealing on the microstructural evolution, mechanical properties, and corrosion resistance of SLM-ed 316L SS specimens. The exceptional ultimate tensile strength (807 MPa) and good elongation (24.6%) of SLM-ed 316L SS was achieved by SLM process and annealing treatment at 900 °C for 1 h, which was attributed to effective dislocation strengthening and grain boundary strengthening. During tensile deformation, annealed samples exhibited deformation twinning as a result of the migration from high-angle grain boundaries to low-angle grain boundaries, facilitating the α′-martensite transformation. Consequently, a deformation mechanism model is proposed. The contribution of dislocation strengthening (~61.4%) is the most important strengthening factor for SLM-ed 316L SS annealed 900 °C for 1 h, followed by grain boundary strengthening and solid solution strengthening. Furthermore, the corrosion resistance of SLM-ed 316L SS after annealing treatment is poor due to its limited re-passivation ability.