Tensile, fracture, and fatigue crack growth properties of a 3D printed maraging steel through selective laser melting

The microstructure and room temperature mechanical properties of a18Ni (300) grade maraging steel (MS) fabricated using the selective laser melting (SLM) technique were studied, in both before- and after-aging conditions. Microstructural analysis reveals fine cellular structure in the as-SLM MS. Upon aging, nanoscale precipitation of intermetallic compounds occurs within the cells, which in turn, result in marked improvements in yield and ultimate tensile strengths, substantial reductions in ductility and fracture toughness, and a transition from dimple to quasi-cleavage fracture morphology. Overall, the mechanical performance, including the fatigue crack growth characteristics, of the SLM MS after aging is found to be similar to that of conventionally manufactured MS of the same grade. Importantly, the reduced ductility does not lead to a reduction in toughness, attributed to the stress induced martensitic transformation as a result of austenite presence in aged SLM MS. Although the SLM alloy possesses a mesostructure, which is a result of line-by-line laser scanning and layer-by-layer building of the components, no significant anisotropy in the mechanical behavior is observed, which is a result of strong metallurgical bonding between adjoining lines and layers. These results are discussed in terms of the meso- and micro-structural features.