Effect of heat treatment on microstructure and corrosion properties of double-wire GTA additive manufactured 308L stainless steel

Heat treatment is a critical approach to improve the microstructure and properties of SS308L fabricated in double wire gas tungsten arc additive manufacturing (DW-GTA-AM). The influence of heat treatment on the microstructure and corrosion properties of SS308L was studied. The microstructures of the samples heat treated at 1000, 1050 and, 1100 ℃ for one hour consist of δ ferrite and austenite, and δ ferrite spheroidizes gradually. Compared with the as-deposited sample, the amount of δ ferrite is negatively correlated with the heat-treated temperature. Potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) measurements indicate that the corrosion resistance increases along with the heat-treated temperature, which can be attributed to that a higher heat-treated temperature results in a thicker and more compact passive film, dissolution of more δ ferrite, and better element diffusion. The corrosion resistance of SS308L is mainly affected by the secondary phase and element distribution.