Effect of annealing temperature on tensile and impact properties of S31803 duplex stainless steel

Duplex stainless steels (DSSs) are characterized by a two-phase microstructure of ferrite and austenite, the fractions and compositions of which are known to control mechanical properties and corrosion resistance. This study investigated the tensile behavior and impact toughness of a standard DSS S31803 by analyzing microstructure and evaluating strengthening mechanisms in each phase as well as the stacking fault energy (SFE) of austenite. Annealing temperature changed the volume fractions and compositions of ferrite and austenite, and significantly affected both tensile and impact properties. As the annealing temperature increased, ferrite fractions and nitrogen contents in both phases rose, which improved yield strength dominantly by solid solution strengthening. Moreover, the hardness difference between the two phases became more pronounced, which intensified strain partitioning. The SFE of austenite ranged 21-48 mJ m-2, and mechanical twinning was activated; however, the influence of SFE on tensile properties was not as significant as in lean DSSs cases in which strain-induced martensitic transformation occurred. To improve impact toughness, secondary phases should be absent and a high fraction of austenite should be present. Consequently, 1000 degrees C, the lowest annealing temperature that could avoid detrimental secondary phases, achieved good strength-ductility combination as well as superior impact properties.