Process parameter optimization and mechanical properties for additively manufactured stainless steel 316L parts by selective electron beam melting

Abstract

This work presents an experimental study of process optimization of the pair of critical parameters (speed function (SF) and focus offset (FO)) for stainless steel 316 L (SS316L) parts additively manufactured by selective electron beam melting (SEBM). Here, there are two sets of optimized SF-FO parameters that could build SS316L parts with high relative densities (>99%) and well-melted top build surfaces. Tensile test results show that most of the SEBM-built SS316L samples exhibit higher tensile strengths than the conventional cast and wrought counterparts, whereas their ductility is lower. In addition, strong anisotropic tensile properties are observed for the SEBM-built SS316L samples, e.g. they generally have better tensile properties when loaded parallel to the build direction as compared to the horizontal direction. However, a large number of σ phase was found to precipitate at grain boundaries in the SS316L samples fabricated under lower SF and larger FO with a higher build temperature, which evidently deteriorates their tensile properties particularly for the horizontal direction. It is suggested that SEBM process parameters for SS316L must be optimized to avoid σ phase precipitation at elevated temperatures apart from a well-melted top build surface and a high relative density.