Development and post-process heat treatment of dissimilar steel structure via twin-wire arc additive manufacturing using heterogeneous functionally graded deposition strategy

Optimizing the existing wire arc additive manufacturing (WAAM) with development of specialised deposition strategies for obtaining engineered materials with graded properties can significantly contribute to the process efficiency specially in reducing processing speeds owing to the simplicity of process, enhancing material usage efficiency, fabricating products of better structural integrity, ease of adaptation of process, enabling multi-materials in a single product, and so on. In this research, twin-wire arc additive manufacturing (t-WAAM) using functionally graded deposition (FGD) and optimal post-process heat treatment strategy is chosen to achieve alloys with considerably enhanced interfacial strength and customized properties. Controlled spatial composition and microstructure variations are undertaken to achieve tailored properties that smoothly vary throughout the deposited component. This work reports FGD steel structure fabricated using t-WAAM with two dissimilar steels (SS316LSi and ER70S-6). Heat treatment was applied to the FGD interface at 950°C and 1100°C, respectively, followed by forced argon cooling to improve the mechanical characteristics, phase transformation, and microstructure. The deposited structure had polygonal ferrites, dense pearlite structures at higher temperatures, and columnar to isotropic transition. Heat treatment, notably at 11000 C, caused dendritic arm disintegration and columnar features to decrease, affecting grain shape and their development. On the SS316Si side, enhanced elongation was observed due to the heat treatment-induced decrease in volume % of δ-ferrite. A thorough investigation establishes that heat treatment significantly impacts FGD interface, microstructure, mechanical characteristics, and phase transformation, offering crucial novel information about the behaviour of developed FGD in structural applications.