Effect of scanning speed on the microstructure and mechanical behavior of 316L stainless steel fabricated by selective laser melting

In this work, the tensile behavior and microhardness of 316L stainless steel fabricated by selective laser melting under different process parameters were investigated. The ultimate tensile strength decreased slightly with increasing energy input, while the opposite tendency was observed for the elongation to failure. Microstructure characterizations were performed to relate the pore morphology, melting pool geometry, solidification cell structure, and grain sizes to the mechanical performance of as-built samples. Fine grains with high fraction of low-angle grain boundaries and fine cellular structures with nano-inclusions are observed in the sample fabricated with a high scanning speed (1000 mm/s). As a result, the sample shows high ultimate tensile strength of up to 707 MPa, while maintaining a total elongation of 30%. The sample fabricated with a low scanning speed (800 mm/s) shows high ductility with total elongation to failure of 55%. The improved ductility is mainly attributed to the elimination of residual pores and melting pool boundaries, which result in brittle features in the as-built samples. The results indicate that selective laser melting may act as a physical metallurgy method to modify the microstructure, and thus improve the mechanical performance of metallic materials.