Understanding microstructural evolution and metallurgical challenges in wire-arc directed energy deposition of 430 ferritic stainless steel

This study investigates wire arc additive manufacturing (WAAM) also known as wire-arc directed energy deposition (WA-DED) of type 430 ferritic stainless steel, with a focus on the microstructural characteristics and mechanical behavior of the printed component. The WAAM system utilized a gas metal arc welding (GMAW)based approach to produce a single-track multi-layer component. Microstructural analysis was conducted using a dual approach, combining Thermo-Calc/JMatPro calculations for theoretical insights, and light optical microscopy, field-emission scanning electron microscopy (FESEM), and electron backscatter diffraction (EBSD) for experimental investigations. The microstructure of WAAM-printed 430 steel is characterized by the formation of large columnar alpha-ferrite grains decorated with fine intragranular Cr-rich carbides, grain boundary martensite, and the formation of a precipitation-free zone (PFZ) near the martensite layer. These microstructural features of WAAM-printed 430 steel resulted in deficiencies in ultimate tensile strength and ductility, compared to wrought AISI 430 steel. The study highlights the need for implementing an effective strategy for grain refining and designing a tailored post-build heat treatment to enhance the strength and ductility of the printed 430 ferritic stainless steel.