On microstructure, crystallographic orientation, and corrosion properties of wire arc additive manufactured 420 martensitic stainless steel: Effect of the inter-layer temperature

Abstract

In this study, the effects of inter-layer temperature variation on the microstructure, crystallographic orientation, and corrosion performance of a multilayer single-pass wall-shaped 420 stainless steel part fabricated using wire arc additive manufacturing (WAAM) were investigated. The microstructural evolution and texture formation after fabrication were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD) analysis. The microstructural characterization revealed the formation of a martensitic matrix with delta ferrite and retained austenite as secondary phases as a result of complex thermal history experienced by deposited layers through subsequent reheating and cooling during the fabrication process. The samples deposited at the inter-layer temperature of 200 °C exhibited anisotropic crystallographic behavior, while a relatively isotropic texture was observed for the samples fabricated at the inter-layer temperature of 25 °C. To characterize the electrochemical response of the fabricated samples, open circuit potential (OCP), potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) tests were conducted on the prepared samples in naturally aerated 3.5 wt% NaCl electrolyte at ambient temperature. The volume fraction of the retained austenite phase was found to increase by increasing the inter-layer temperature from 25 °C to 200 °C, contributed to the enhanced corrosion performance of the fabricated wall. Localized corrosion attacks were primarily detected adjacent to the delta ferrite phase, regardless of the implemented interlayer temperature during the fabrication process.