Deposition of Manganese and Cobalt on Ferritic–Martensitic Steels via Pack Cementation Process

Abstract

Heat resistant ferritic–martensitic steels are of great interest for many applications at high temperatures. The working temperature of modern solid oxide fuel cells has decreased from 1,000 to 600–800 °C, which allows the application of ferritic steels for use as interconnect materials. Another possible application is for superheaters in fossil fuel power plants. However, such environments often contain a high amount of water vapor, which is known to promote the formation of volatile chromium species CrO₂(OH)₂ leading to insufficient oxidation resistance of Cr-steels. Spinel phases at the surface are believed to suppress this evaporation. Reference oxide samples were prepared to investigate the kinetics of the weight changes of chromia, manganese oxide, MnCr₂O₄-phase and MnCo₂O₄-phase without the influence of the substrate material. These samples were exposure to synthetic air with 10 % water vapor at 800 °C. The results confirm that an enrichment of manganese and cobalt in the metal subsurface zone can play a beneficial role. The diffusion of these elements via pack cementation into the steel subsurface zone is presented for conditions where the bulk phase is not altered.