In situ alloying of a CrMnNi steel via electron beam powder bed fusion process—microstructure and mechanical properties

Abstract In the present study a metastable austenitic stainless steel X2CrMnNi16-7–4.5 was investigated. The alloy composition was adjusted by mixing steel powder X2CrMnNi16-7–9 and steel powder X2CrMnNi16-7–3, whereby the first steel exhibits a primary-austenitic and the latter one a primary-ferritic solidification of the melt, in order to achieve a fine-grained, predominantly austenitic microstructure. After mixing of the powder blend the material was subsequently processed by in situ alloying during powder bed fusion electron beam melting (PBF-EB/M), using two different build parameter sets. The study demonstrates how powder blending and in situ alloying can be used to tailor microstructural features like grain size, texture and phase composition in PBF-EB/M processing by changing the chemical composition of an alloy. The microstructure and phase composition of manufactured specimens were examined by different techniques, including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), electron backscatter diffraction (EBSD) and measurements of ferromagnetic phase content. The steel was predominantly austenitic and exhibited a fine-grained microstructure for one of the build parameter sets, with a slight < 011 > texture in build direction (BD) after the PBF-EB/M process. Mechanical properties of alloy X2CrMnNi16-7–4.5 were characterized by tensile as well as low cycle fatigue (LCF) tests. In tensile tests the material possesses excellent mechanical properties due to the occurrence of the TRIP (TRansformation-Induced Plasticity) effect under loading, whereby the orientation of the loading axis (LA) relative to the build direction plays a detrimental role. Fatigue tests revealed that surface polishing did not show any improvement in fatigue lifetime compared to the as-built specimens with a natural surface, which was attributed to the presence of numerous inclusions and lack of fusion (LOF) defects.