Anisotropic response of additively manufactured 316 L stainless steel towards low-temperature gaseous carburization

Abstract

In order to modify the surface properties of austenitic stainless steel fabricated by Laser Powder Bed Fusion (L-PBF), low-temperature gaseous carburization (LTGC) was employed. During LTGC, a carburized case of expanded austenite forms at the surface, which contains a high surface carbon content (∼2.5 wt%), high nano-hardness (∼12.6 GPa), large compressive residual stresses (from −2.4 GPa to −3.2 GPa), and is free of carbide precipitates. In the expanded austenite zones, different residual stresses were measured with X-ray diffractometry (XRD) for the top plane, i.e. in the plane perpendicular to the build direction, and for the side plane. This anisotropy is suggested to be caused by grain-shape anisotropy for the different specimen planes and inherent to the hierarchical microstructures resulting from L-PBF.