Cracking Failure in WAAM Maraging 250 Steel Under Near-Immersion Active Cooling

This work investigates the cracking mechanism in a WAAM-fabricated 18Ni-250 maraging steel wall produced under near-immersion active cooling (NIAC), focusing on the combined role of residual stresses, microporosity, and local chemical heterogeneities. Non-destructive portable x-ray diffraction revealed high tensile residual stresses at the wall base, particularly along the build direction. Optical microscopy showed a non-uniform porosity distribution, with a higher pore concentration near the cracked region, where a relative density of approximately 85% was measured. Fractographic analysis indicated brittle fracture features, while EDS mapping revealed local Ti- and Mo-enriched regions aligned with the crack path. The results indicate that cracking in WAAM maraging steel results from the combined effect of tensile residual stresses, volumetric microporosity, and local chemical segregation.