Effect of Water Vapor in Air on the Oxidation Behavior of Ferritic Stainless Steels for SOFC Interconnects

In the attempt to develop materials for interconnects of planar-type solid oxide fuel cells (SOFC), the oxidation behavior and scale electrical properties of four, commercially available, ferritic stainless steels were investigated by oxidizing at 800 degrees C for times up to 900 h in the dry and wet air environments. The growth kinetics of oxide scales were significantly deviated from the parabolic growth law, exhibiting the temporal growth exponent being much less than 0.5. Titanium addition in ferrite stainless steels was detrimental to oxidation resistance since its fast out-diffusion onto the scale surface enhanced the scale growth. For the alloys without Ti contents, the presence of water vapor in the oxidizing environment enhanced the scale growth rate, but it resulted in a drastic, microstructural change of oxide scale that consisted of Cr2MnO4 spinel and Cr2O3, which in turn lowered the area specific resistance (ASR) and the apparent activation energy for conduction.