Effect of laser remelting on the surface characteristics of 316L stainless steel fabricated via directed energy deposition

Abstract

Herein, laser remelting (LRM) technology was adopted for the stainless steel 316L deposited using the directed energy deposition (DED) process. We focused on examining the scanning direction, laser power, and overlap, which are the main parameters of LRM, and changes in the surface characteristics after LRM. The LRM could remove the traces of the spatter, unmelted powder, and deposited tracks remaining on the DEDed surface. Moreover, overlap was the major factor affecting the surface roughness and waviness. The roughness and waviness of the LRM-treated surface decreased as the overlap increased. An interaction was observed between the laser power and overlap in terms of the surface roughness, and when the laser power was high and the overlap was large, the surface roughness was low. Furthermore, the laser power of 1200 W transferred the excess energy to the surface, reducing the surface improvement. After performing LRM, the thermodynamically unstable crystal grains recrystallized. From the X-ray diffraction results, face-centered cubic and body-centered cubic phases were observed; however, no difference was observed in the phase fraction ratio before and after the LRM treatment. Regarding residual stress measurements, no obvious effect was observed on the removal of tensile residual stress formed on the as-prepared surface. For this reason, the change in hardness after LRM was not significant (increased by 10.7%). However, the costs of postprocessing, such as machining and grinding, can be partially reduced using LRM after DED processing.