Microstructural Evolution and Mechanical Behavior of Additively Manufactured 316 L Subjected to Varied Deformation Directions

The present work investigates the effect of deformation directions on the microstructure and mechanical properties of 316 L stainless steel processed by additive manufacturing (AM). It is found that crossly rolled AM 316 L after thickness reduction of 10% demonstrates an enhanced density of deformation twins along the different directions and a substantial hardness increment (108.6 HV, ~ 48.5%). The cross rolling process effectively raises the twinning Schmid factors, the fraction of grains in high twinning Schmid factor regions and activates the generation of multiple twinning systems. The deformation twins with multiple twinning systems have a better capacity in storing the dislocations than that with single twinning system during deformation. Thus, the large increment of hardness after small deformation using cross rolling can be ascribed to increased dislocation and twin densities while the elevated dislocation density is also assisted by the presence of multiple deformation twins. The present work suggests that the multiple deformation twinning of austenitic steel with hierarchically heterogeneous microstructure processed by AM can be effectively activated under small deformation of cross rolling, which may be also applicable for other face centered cubic metallic materials with low stacking fault energy.