Effect of the Tempering Process on the Corrosion Performance of Wire Arc Additively Manufactured 420 Martensitic Stainless Steel

Abstract

With the aim of modifying the microstructure and improving the corrosion performance of a wire arc additive manufactured 420 martensitic stainless steel, heat treatment cycles consisting of austenitizing at 1,150°C followed by air cooling and subsequent tempering at different temperatures (300°C, 400°C, 500°C, and 600°C) were applied to the as-printed alloy. Microstructural analysis revealed that the austenitization and subsequent air-cooling treatment led to the removal of retained austenite and delta ferrite from the as-printed structure, while the tempering process resulted in the precipitation of a variety of carbide particles at different tempering temperatures. Electrochemical tests performed in an aerated 3.5 wt% NaCl solution showed that tempering at 400°C led to the highest corrosion resistance, while tempering at 500°C deteriorated the alloy’s resistance against localized corrosion. The most stable passive layer was found to form on the 400°C tempered sample due to the uniformity of Cr-concentration in the formed carbide precipitates and their surrounding matrix. However, Cr-rich carbide precipitates formed in the 500°C tempered sample were found to deteriorate the passive film stability throughout the immersion time in the electrolyte.