High temperature corrosion of wrought and wire arc additively manufactured 316L stainless steel in a simulated boiler environment

Abstract

In this decade, the working temperature of the power plants significantly increased to above 700 °C to enhance efficiency. The corrosive species deposits on the hot section components were prone to corrosion damage at elevated temperatures. This study investigates the microstructure and high-temperature corrosion characteristics of the wrought and wire-arc additive manufactured (WAAM) 316L stainless steel in an aggressive molten Na2SO4 + 25% NaCl salt and air environment at 750 °C. The corrosion rate of both wrought and WAAM-built 316L was higher in the molten salt (MS) environment compared to air due to the chloride and sulfate deposits. The wrought 316L was severely prone to corrosion damage with spallation and cracking, which was attributed to the dissolution of the non-protective Fe2O3 scale by Cl. The WAAM-built 316L showed the lower oxidation and depth of corrosion attack in both air and MS environments than the wrought steel due to the fine dendrite grains, resulting in the outward diffusion of more Cr. The accelerated degradation occurred on the WAAM and wrought 316L SS in MS condition due to the dissolution of Cr2O3 and the faster inward diffusion of Na+. The detailed oxide growth, internal corrosion attack, and oxide failure mechanisms of the steels were explored in the air and MS conditions.