Isolating specific microstructure effects on observed enhanced mechanical strength of additively manufactured 304L stainless steel

Additive manufacturing (AM) is a fabrication route that provides efficient and cost-effective ways to manufacture complex metallic components for engineering applications. The choice of the process parameters dictates the final microstructure of AM materials. In addition, repeated melting and solidification at high cooling rates during the AM fabrication process results in microstructures that can deviate largely from traditionally produced wrought or cast materials. For example, the unique microstructural features of AM 304L steel include a tortuous grain structure, high dislocation density and increased ferrite fraction relative to wrought material. Process induced microstructural heterogeneity controls mechanical properties, such as the enhanced mechanical strength observed in AM materials. In this study, we developed post processing heat treatment recipes to tailor mechanical properties of post-build AM metallic materials. We performed in-situ neutron diffraction during heat treatment of AM 304L to selectively remove individual microstructural features followed by in-situ deformation in order to assess the role each feature plays in increasing the strength of the material relative to its wrought counterpart.