Effect of heat input on microstructures and mechanical properties in wire arc additive manufacturing of Co-free maraging steel

The heat input is closely related to the microstructure and mechanical properties of Wire Arc Additive Manufacturing (WAAM) products. To investigate the influence mechanism of heat input on the microstructure and mechanical properties of Co-free maraging steel in WAAM, three thin-walled components under the varying heat inputs were fabricated. A systematic analysis of the microstructure and mechanical properties was conducted using numerical simulations combined with multiple characterization methods. The results indicated that the component with the lowest heat input (342 J/mm) exhibited the most favorable mechanical properties, achieving a tensile strength of 1249 MPa and an impact toughness of 62.5 J/cm 2 . The properties progressively deteriorated with increasing heat input. Microstructural analysis revealed that the high cooling rate under low heat input effectively refined the grains, the primary dendrite arm spacing was reduced, and simultaneously increased proportion of high-angle grain boundaries and dislocation density, thereby enhancing the material strength and toughness. Furthermore, WAAM components exhibit pronounced microstructural variations across different orientations, leading to anisotropic mechanical properties. Under low heat input conditions, the lower texture strength significantly reduced anisotropy, with a 31 % decrease compared with that of the higher heat input components (497 J/mm). This study elucidates the mechanism by which heat input influences the mechanical properties through microstructural regulation, providing theoretical foundations for the process optimization of Co-free maraging steel in WAAM.