Impact of active cooling and CTWD on phase stability and fracture behavior of WAAM-fabricated maraging steel 250

To investigate the effect of deposition parameters under near-immersion active cooling (NIAC) assisted Wire Arc Additive Manufacturing (WAAM) on phase stability and mechanical behavior, maraging 250 steel preforms were produced under controlled deposition conditions. WAAM was conducted with a constant interpass time, while welding current and contact tip-to-work distance (CTWD) were varied to modify the local thermo-metallurgical conditions. Microstructural characterization was performed using optical microscopy, scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD) with Rietveld refinement. Mechanical behavior was evaluated by tensile testing, Vickers microhardness measurements, X-ray diffraction residual stress analysis, and crack tip opening displacement (CTOD) testing. Both deposition conditions resulted in a predominantly martensitic matrix in the as-deposited state, with residual retained austenite and Fe–Mo-rich intermetallic phases indexed as sigma-type phases. The condition employing higher current and shorter CTWD exhibited a higher fraction of Fe–Mo-rich secondary phases and increased crystallographic distortion, indicating a strong sensitivity of phase evolution to deposition conditions under NIAC-assisted processing. From a mechanical standpoint, both conditions exhibited high strength and moderate ductility, with statistically comparable hardness and similar fracture resistance as assessed by CTOD. Residual stress measurements revealed compressive stresses in both conditions, with a higher compressive magnitude for the lower-current condition. Overall, the results demonstrate that deposition parameter selection under NIAC-assisted WAAM significantly influences phase constitution, local microstructural heterogeneity, residual stress state, and the mechanical response of maraging 250 steel.