Effect of in-situ rolling and heat treatment on microstructure, mechanical and corrosion properties of wire-arc additively manufactured 316L stainless steel

Post-heat treatment and in-situ rolling, both can be used to improve the coarse grains and anisotropy that are prevalent in metallic materials, fabricated by wire and arc additive manufacturing (WAAM). In this study, the effect of in-situ rolling and heat treatment on the microstructure, mechanical and corrosion behaviors of WAAM 316L was investigated. The results showed that the microstructure of WAAM 316L changed considerably due to the introduction of rolling deformation, as it was observed that the ferrite was distributed in a reticulated or equiaxed morphology instead of dendritic distribution, columnar grains were found to be engulfed, while a large number of low angle grain boundaries (LAGBs) with high dislocation density were introduced. After heat treatment at 650 °C, there was no significant change in grain morphology, ferrite gradually transformed into σ phase, the tensile strength increased, yield strength and elongation decreased. After heat treatment above 1000 °C, the strength and ductility of the rolled WAAM 316L were higher than those of the unrolled WAAM 316L. As the heat treatment temperature increased, the corrosion resistance first decreased and then increased. In-situ rolling resulted in a decrease in the corrosion current density of the steel and also reduced the stability of the passive film.