Scan Strategy Effect on the Mechanical Properties and Microstructure of Directed Energy Deposited 18Ni300 Maraging Steel

Although the laser scan strategy does not affect the energy density of laser-based additive manufacturing, changes in laser scan direction critically influence the residual stress and microstructure of metallic components. However, only a limited number of studies have investigated the role of laser scan strategy on the microstructure and mechanical properties of additively manufactured maraging steels. Therefore, this study examines the effect of laser scan strategy on the mechanical properties of 18Ni300 maraging steel. Different laser scan strategies influence the morphologies of the molten pool, where retained austenite is concentrated in 18Ni300 maraging steel. The 45o sample exhibits a denser molten pool distribution compared to the other samples due to reduced layer overlapping. Because of the plastic strain incompatibility between martensite and austenite at the molten pool boundary, this dense molten pool distribution in the 45o sample resulted in the highest back-stress hardening. Additionally, the minimal layer overlapping in the 45o sample reduces heat exposure during laser-based additive manufacturing, leading to a finer martensite block and lath size. By combining high back-stress hardening with a fine martensite block and lath size, the 45o sample achieved the highest tensile property compared to the other samples. These results indicate that the selection of laser scan strategy is crucial for designing a heterogeneous microstructure in additively manufactured parts, which can enhance mechanical properties, even with the same energy density.