On the microstructural stability of metastable CrMnNi steels processed by laser-based additive manufacturing techniques

Beam-based additive manufacturing (AM) techniques in general are characterized by small melt pool sizes and concomitantly high cooling rates leading to unique microstructures. Although, depending on the utilized technique, the resulting microstructures can be highly different from each other, AM-built materials are often characterized by an improved chemical homogeneity in contrast to conventional manufactured counterparts. In combination with a high dislocation density, that can be found in processes such as the laser-based powder bed fusion of metals (PBF-LB/M), these microstructural features will directly influence the mechanical behavior. Especially, metastable CrMnNi steels, whose deformation behavior is often assisted be twinning or transformation-induced plasticity, are sensitive to their microstructural features. In the present study, the influence of different beam-based AM methods such as PBF-LB/M and directed energy deposition (DED) on the microstructural evolution of CrMnNi steels is investigated. Based on different chemical compositions, the stability of the austenitic phase was varied leading to different dominant deformation mechanisms (dislocation glide, twinning or phase transformation) under quasi-static loading. The presence of different sized microstructural features leads on a macroscopic scale to a highly different deformation behavior that can be traced back to the employed process. The results presented on AM materials are compared with conventional counterparts from literature.