Influence of build orientation and thermal treatment on the fracture toughness of LPBF-manufactured 18Ni300 maraging steel

This study investigates the fracture behavior of 18Ni300 maraging steel manufactured via LPBF, comparing specimens on as-built condition and solubilization and aging treated. Specimens were fabricated in vertical and horizontal orientations, and fracture toughness was assessed using the crack tip opening displacement (CTOD) method. Comprehensive microstructural characterization was performed to evaluate microstructure, and fracture surface features. Results revealed anisotropic fracture behavior in the as-built condition, attributed to misalignment of the crack propagation paths with the melt pool boundaries. In contrast, heat-treated specimens exhibited a reduction in ductility and fracture toughness (CTOD values decreasing by up to 97 %), which was attributed to microstructure coarsening and martensite stabilization. Fractographic examination revealed a transition from ductile failure (characterized by plastic deformation and dimple coalescence) in the as-built condition to brittle features after thermal treatment. These findings reveal that fracture mechanisms in LPBF 18Ni300 are highly sensitive to microstructural features, which are governed by build orientation and heat treatment. This study reinforces the applicability of CTOD as a robust method for evaluating fracture performance in AM metallic components, providing insights into the interdependencies among processing conditions, microstructure evolution, and mechanical integrity. Furthermore, this study validates the use of CTOD method for reliable fracture toughness assessment in LPBF components, addressing the current scarcity of validated fracture mechanics by this method and providing a robust and reliable foundation for future structural integrity analyses of LPBF 18Ni300. • Crack Tip Opening Displacement (CTOD) (δ parameter) assessment for LPBF 18Ni300 maraging steel fracture toughness evaluation. • Deepening the relationship between microstructure and mechanical properties of maraging steel LPBF-printed. • Correlation between build orientation and solubilization and aging treatments effects on fracture toughness behavior. • Up to 97 % fracture toughness reduction observed after heat treatments. • Findings support design and qualification of high-strength AM structural components.