The effect of micro- and mesoscale heterogeneity on the fracture of laser powder bed fusion processed duplex stainless steels

The fracture behavior of a duplex stainless steel processed by laser powder bed fusion (LPBF) from mixed 25Cr + 5 wt.% Ni powders (i.e., 25Cr-5Ni) was compared to 25Cr that was processed without Ni but additionally heat-treated (i.e., 25Cr-HT) to give similar phase fractions of austenite and ferrite but with different micro and mesostructures. The 25Cr-5Ni alloy exhibited high yield strength (828–958 MPa) and good fracture toughness (122–167 MPa√m) while requiring no post heat-treatment after LPBF fabrication. In contrast, the 25Cr-HT alloy gave somewhat lower strength and higher fracture toughness in a classic strength-toughness trade-off due to the elimination of the high dislocation density from the LPBF process. While powder mixing induces somewhat more anisotropic properties due to a coarser mesostructure phase distribution, the results demonstrate an approach to develop LPBF processed duplex stainless steels that don't require costly post heat treatments.