D. Schmidt , M. Galetz, M. Schütze
Oxidation of Metals 79 (2013), 589-599, DOI: 10.1007/s11085-012-9340-4
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.