Microstructural evolution and mechanical properties of circular disc fabricated by multi-layer multi-track cold metal transfer wire arc additive manufacturing

The study investigates the microstructural evolution and mechanical performance of a multi-track, multi-layer circular disc fabricated from low-carbon steel (ER70S-G) using the cold metal transfer wire arc additive manufacturing (CMT-WAAM) process. The layers were deposited on a rotating substrate using a five-step, inward–outward alternating deposition strategy. Microstructural analysis revealed ferrite as the predominant phase, with localized acicular ferrite and bainite near fusion boundaries. Hardness measurements showed values ranging from 183 HV to 238 HV along the build direction and 190 HV to 232 HV along the deposition direction, with the middle zone exhibiting the lowest hardness due to slower cooling and prolonged thermal cycling. Tensile testing demonstrated yield strengths of 313.15 MPa (0° orientation) and 350.57 MPa (30° orientation), with ultimate tensile strengths of 593.75–617.08 MPa and comparable elongation (∼28–31%). Fractographic analysis confirmed ductile failure in both orientations. The results establish a direct correlation between localized thermal history, microstructural evolution, and spatial property variation in complex CMT-WAAM geometries, providing insights for optimizing mechanical uniformity in curved components.