On the microstructural characteristics and corrosion performance of as-printed and heat-treated PH 13–8Mo martensitic stainless steel fabricated by wire arc additive manufacturing

In this study, the effect of post-printing solution and aging treatments on the microstructure and corrosion properties of a wire arc additive manufactured PH 13–8Mo martensitic stainless steel were investigated. With the purpose of eliminating the microstructural heterogeneities, and columnar/textured structure in the as-printed material, post-printing heat treatment cycles comprised of solution treatment for 1 h at different temperatures (950, 1050, and 1200 °C), followed by aging process for 4 h at 400, 500, and 600 °C were applied on the as-printed material. The microstructural studies revealed that the solution treatment at 1050 °C could eliminate the columnar structure and removed the undesired residual delta ferrite phase from the microstructure of the alloy. Further aging process resulted in a coarser martensite lath structure at 400 °C, precipitation of β-NiAl phases at 500 °C, and formation of reverted austenite and M23C6 carbides at 600 °C. The effects of different microstructural features on the corrosion response of the as-printed and heat-treated samples were investigated using different electrochemical measurements, i.e., open circuit potential, potentiodynamic polarization, electrochemical impedance spectroscopy, and Mott-Schottky tests. The electrochemical responses obtained from different samples showed that the elimination of Cr-enriched delta ferrite from the as-printed sample significantly improved the corrosion performance of the heat-treated samples, while the formation of M23C6 carbides at the highest aging temperature (600 °C) triggered the sensitization phenomena and consequently impaired the corrosion resistance of the material.