Metallurgical and mechanical property characterization of additively manufactured 304L stainless steel

Abstract

Utilization of austenitic stainless steels as a structural material is common across many industries due to the exceptional combination of strength, ductility, toughness, corrosion resistance and weldability. Recent improvements in the capabilities of metal additive manufacturing (AM) has brought these materials into focus for potential additional structural applications. Although the mechanical properties and solidification behavior is well understood for traditionally manufactured components, the same understanding is not directly transferable to an additively manufactured part. Deposits of 304L stainless steel were made from the same powder feedstock, using both Laser Powder Bed Fusion (L-PBF) and Laser Powder Directed Energy Deposition (LP-DED). Initial mechanical and metallographic testing results revealed a consistent anisotropic behavior related to the build direction as well as differences in solidification behavior between the two processes. Analysis of the solidification morphologies revealed that current predictive methods developed for welding can be applied to powder-based AM processes to predict the solidification morphology. \textit{In-situ} tensile testing with simultaneous electron backscatter diffraction (EBSD) allowed for observation of the deformation mechanisms that occur in both orientations. Through these tests, it was observed that deformation twinning occurs preferentially over slip in the as built direction, lowering the initial strain hardening rate of the material.