Characterization of the Interface between WAAM-Deposited Carbon Steel and S355 Structural Steel Plate

This study investigates the microstructural and mechanical integrity of the interface between Wire Arc Additive Manufactured (WAAM) carbon steel (CS) and an S355 structural steel (Wrought CS) plate, with emphasis on the suitability of WAAM for repair and reinforcement of structural components. A wall structure was deposited on a Wrought CS plate using a Cold Metal Transfer (CMT) process and subsequently characterized through microstructural analysis, hardness measurements, tensile testing, and bending fatigue testing. The microstructural observations revealed a smooth and defect-free transition across the interface, consisting of a fine-grained heat-affected zone (HAZ) formed by partial recrystallization. The hardness profile exhibited a continuous gradient, with slightly elevated values near the interface (~210 HV), indicating grain refinement and the absence of softening effects. The tensile results showed that the WAAM-deposited CS possessed higher strength and ductility than the Wrought CS, while the hybrid WAAM CS–Wrought CS specimens displayed intermediate properties. Fracture consistently occurred within the Wrought CS plate rather than at the interface, confirming a metallurgically sound and mechanically robust bond. Under bending fatigue loading, the WAAM CS demonstrated the highest fatigue limit (~250 MPa), followed by the hybrid (~205 MPa) and Wrought CS (~162 MPa). All hybrid specimens fractured on the Wrought CS side, indicating that the interface remained intact under cyclic stress.