This study investigates the relationship between microstructure and mechanical properties in a novel metastable austenitic steel alloy manufactured through electron beam powder bed fusion (PBF-EB/M). The alloy was mixed from existing powders of low-carbon, high-alloy CrMnNi steels with varying nickel and silicon contents enabling a defect tolerant behaviour due to TRIP (TRansformation Induced Plasticity) effect during mechanical loading. 

Two steel powders X2CrMnNi 16-7-3 and X2CrMnNi 16-7-9 were blended in a 4:1 ratio utilizing a drum mixer. The latter and similar materials have already been studied in detail. The resulting powder blend with the chemical composition X2CrMnNi 16-7-4.5 was processed in an Arcam A2X (GE Additive, Sweden).

Tensile tests revealed anisotropic material behaviour, where specimens orientated parallel to the building direction (BD) exhibit lower strength and ductility compared to specimens oriented parallel to the BD due to the orientation of lack-of-fusion defects. Fracture surface analysis showed AM typical cavities such as lack of fusion and gas pores, but also non-metallic inclusions. Specimens oriented parallel to the BD showed a tensile strength exceeding 900 MPa and elongation to failure more than 50 %. This behavior can be attributed to the strain-induced martensitic phase transformation ocurring during mechanical loading.

The microstructural analysis of the material was conducted using electron back-scattered diffraction (EBSD). The steel exhibits a fine grained morphology and the grains are slightly elongated along the build direction. Notably, the texture of the grains is characterized by a preferred <011> crystallographic texture along the build axis, although the intensity varies with part size and build parameters.

Chemical homogenity of parts can be confirmed by energy dispersive spectroscopy (EDS), also showing a decrease in manganese content due to evaporation during the build process. Elevated beam energies lead to an enhanced manganese evaporation resulting in lower austenite stability and higher capability for martensitic phase transformation. Furthermore, increased beam energy in the contour region results in smaller defects in this area. Positive effects on the cyclic loading behaviour have to be confirmed.