Effect of Surface Treatment on the Corrosion Behavior of Stainless Steels in High-Temperature Supercritical Carbon Dioxide

Abstract

Abstract The corrosion behavior of two stainless steels (310S and alumina-formed 310S) treated by different surface treatment methods (polishing or grinding) has been investigated after exposed to high-temperature supercritical carbon dioxide (sCO2) at 650°C / 20 MPa. The microstructure and microchemistry of materials have been analyzed and compared before and after exposure. The results show that polishing deteriorates the corrosion resistance, while grinding enhances the anti-oxidation and anti-carburization capability of materials. Thick and unprotective Fe-rich oxides are formed on the polished 310S and alumina-formed 310S, which leads to the poor carburization resistance. Much thinner oxides and shallower carburization depths can be observed on the materials treated by grinding. Continuous Cr-rich oxide is formed on the grinded 310S, while outer Cr-rich and inner Al-rich oxides are formed on the grinded alumina-formed 310S. Grinding deforms the surface region of materials. An outer ultra-fine grain layer and an inner highly deformed grain layer are located at the surface, which own fast diffusion paths and enhance the element diffusion rates (especially Cr and Al). This leads to the transition from the formation of unprotective Fe-rich oxide layers to the protective Cr-rich or Al-rich oxide layers, which not only hinders further oxidation of the matrix, but also reduces the carbon permeation. Improved oxidation and carburization resistance therefore occurs on the materials treated by grinding after exposed to high temperature sCO2 environment.