Near-net-shape wire-arc additive manufacturing (WAAM) of bimetallic P22 steel and Inconel 625: microstructure–property correlations

Abstract Wire-arc additive manufacturing (WAAM) is a state-of-the-art near net shape manufacturing technology for manufacturing structures with tailored mechanical properties. However, the process typically requires minor post-processing (e.g., machining) to achieve the desired surface finish and dimensional accuracy. This study investigates the mechanical properties and the concomitant microstructural evolution in a WAAM bimetallic comprising of a low alloy carbon steel (P22) and Inconel 625 nickel alloy (IN625) using gas metal arc welding (GMAW). Microstructural examination revealed distinct microstructural features, including bainite-ferrite morphology in P22 steel and a dendritic γ-austenite matrix in IN625 with intermetallic Laves phase precipitates. The interface exhibited a defect-free metallurgical bond, characterised by martensitic laths within the P22 region, primarily due to rapid cooling, and columnar grains in the IN625 region due to directional solidification. Tensile and Charpy impact tests revealed that IN625 exhibited superior mechanical properties, whereas the bimetallic component displayed moderate strength with reduced ductility. In these tests, fractures appeared to consistently occur on the P22 side, due to the presence of Mn-rich inclusions. Crystallographic texture analysis showed near random texture for the P22 steel, governed by recrystallisation and phase transformation dynamics. In contrast, the texture of the IN625 deposit cannot be concluded due to the small number of directionally grown grains during WAAM.