Cr diffusion coating to improve the corrosion resistance of an ODS steel in super-critical carbon dioxide environment

Abstract

The surface of oxide dispersion strengthened (ODS) steel was deposited with Cr by physical vapor deposition, followed by inter-diffusion heat treatment (Cr-IDHTed) to form a thin outer Cr-rich carbide layer and interdiffusion zone below it. When exposed to super-critical carbon dioxide (S-CO2) environment at 650 degrees C in 20 MPa for 500 h, a continuous and protective Cr2O3 layer was formed on Cr-IDHTed ODS steel, resulting in marked reduction in weight gain compared to the as-received one. On the other hand, thick Fe-rich oxides were formed on the as-received ODS steel, resulting in a significant weight gain. The as-received ODS steel showed near complete loss of tensile ductility after S-CO2 exposure due to extensive carburization in matrix. However, because of the presence of thin Cr-rich oxide layer on the surface, carburization was prevented and the change in tensile properties was minimized for Cr-IDHTed ODS steel.