Corrosion behaviour of wire plus arc additive manufacturing (WAAM) built high strength pipeline steels

Wire and Arc Additive Manufacturing (WAAM) is of interest for many industries that requires parts with complex geometries via metal 3D printing. WAAM is capable of producing metal components with high deposition rates, large build volumes, minimum material waste and lead times and good structural integrity. Previous research in this field has focused on achieving correct geometrical and defect free deposition, while maintaining good mechanical properties when compared with wrought alloy. This is the first investigated study devoted to the corrosion behaviour of WAAM pipeline steels in artificial seawater. The corrosion rate of electrode rod 90 solid (ER90S-G) WAAM deposited low alloy steel (as deposited and heat-treated conditions) were compared to F22 wrought alloy of similar chemical composition. Corrosion behaviour of the low alloy steels were assessed using mass loss and electrochemical characterisation and correlated to the microstructural characteristics and hardness. The experimental results showed improved corrosion resistance and strength in ER90 WAAM built low alloy as compared to the wrought. Optical micrographs and hardness measurements confirmed that a martensitic structure was formed under air cooled condition in as deposited ER90, while tempered-martensitic structures were observed in heat treated ER90 and F22 wrought alloy steels. This research is the first step in creation of corrosion data of WAAM built structures and compare to their wrought version. This underpinning correlation between microstructural variation and corrosion pattern would allow modification of the WAAM process in a suitable manner for successful commercial applications.