Temperature dependence of corrosion of ferritic stainless steel in dual atmosphere at 600-800 °C

The ferritic stainless steel AISI 441 (EN 1.4509) is exposed for 1000 h to air - 3% H2O on one side and to Ar - 5% H-2 - 3% H2O on the other at temperatures 600, 700, and 800 degrees C. Conditions are chosen to mimic the environment of metallic interconnects in an operating solid oxide fuel cell (SOFC). At 600 degrees C, similar to 25 mu m thick Fe2O3/(Fe,Cr)304 forms on large parts of the air side of the samples. Reference samples exposed to air- 3% H2O on both sides form thin protective layers of (Cr,Mn)(3)O-4/Cr2O3 at the same temperature. At higher temperatures, 700 and 800 degrees C, all samples form protective layers of (Cr,Mnt)(3)O-4/Cr2O3 regardless of exposure to single or dual atmosphere. It is concluded that corrosion resistance in a dual atmosphere has an inverse dependence on temperature. Different hypotheses for the underlying cause for the dual atmosphere effect are discussed and compared to the experimental data.