On understanding microstructure and inclusion effects on machinability of additively manufactured 316L stainless steel

Additive manufacturing (AM) enables near-net shape parts with complex geometries, but precision components require machining to meet surface requirements. This study links fabrication-induced microstructures to turning machinability of 316L stainless steel produced by laser powder bed fusion (PBF-LB) and directed energy deposition (DED-LB). Unlike previous studies focusing primarily on grain structure and anisotropy, this work identifies non-metallic inclusions as a governing microstructural factor affecting tool wear during machining of AM 316L. Compared with wrought material, AM materials exhibited columnar grains, higher crystallographic misorientation, and a hardness increase of 100% and 45% for PBF-LB and DED-LB material respectively. In addition, higher densities of oxide inclusions were found in the AM variants, whereas wrought material additionally contained sulfides. Although initial cutting forces differed by less than 10%, tool life tests revealed that additively manufactured materials showed consistently faster flank wear development than the wrought material, resulting in earlier attainment of the wear criterion and tool-life reductions of up to ~57%. Non-metallic inclusions were identified as a major factor governing wear progression, suggesting that limiting oxygen uptake and tailoring inclusions could improve machinability.