Processing optimization, microstructure, mechanical properties and nanoprecipitation behavior of 18Ni300 maraging steel in selective laser melting

Thanks to the application needs of conformal cooling channels in mold field, selective laser melting (SLM) has become a key technique for fabricating novel mold with high cooling efficiency. This work systematically investigates the action mechanism of SLM processing parameters on densification of 18Ni300 maraging steel, and corresponding phase identification, microstructural evolution, nanoprecipitation behaviors and mechanical properties of as-built samples with optimal relative density (RD) before and after solution-aged treatment. Response surface method and analysis of variance are employed to analyze the significance levels of effects for SLM processing parameters on RD. The optimal processing parameter set and resultant RD of 99.45% as well as corresponding processing windows for SLMed 18Ni300 sample can be obtained. It is found that as-built sample consists of major martensite α phase and scarce austenite γ phase. Solution-aged treatment is in favor of reversion of martensite to austenite and precipitation of intermetallic compounds. Both as-built and solution-aged samples exhibit no obvious texture fiber, but there are different grain sizes and orientations. It is worthy noted that the mechanical properties (ultimate tensile strength of ∼1245 MPa) of SLMed 18Ni300 sample are comparable to that of corresponding wrought sample.