Strengths and microstructure of SUS316L fabricated by selective laser melting

Abstract

Recently, AM (Additive Manufacturing) process which can produce highly complex components have been gaining significant attention in both industry and academic research. Numerous metals and alloys have been processed by selective laser melting; Ti alloys, Ni alloys, and Co-Cr alloys have been the subjects of recent work. Ni-based superalloys have precipitated phases such as γ′ and γ″ phase and Ti alloys and Co-Cr alloys are the multiphase alloys which have phase transformation, thus it is difficult to clarify the influential factors of AM process on strengths of these alloys. In this study, we used SUS316L stainless steel which is a single-phase solid-solution alloy and does not have precipitated phase in order to clarify characteristic influential factors of AM compared with a conventional material. SUS316L was fabricated by selective laser melting by ytterbium fiber laser from fine metallic powder. It was found that the coarse columnar grains grew up along the built direction and the columnar cell structure of dislocations which are induced during the AM process. During the solution heat treatment, the dislocation recovery was observed. AM specimens showed higher tensile and creep strengths compared with the conventional (hot working) material because of the high-density of dislocations. Ductility of AM specimens was lower than the conventional material because of defects due to lack of fusion at molten pool boundaries; furthermore, the specimens whose loading direction corresponds to built direction showed lower strength and elongation than the specimens whose loading direction perpendicular to built direction due to the oriented defects.