Effect of pre-oxidation on the oxidation resistance of Crofer 22 APU

The ferritic stainless steel Crofer 22 APU is attractive for the use as interconnects in solid oxide fuel cell stacks. The oxidation rate of this alloy in air at 800 °C was reduced by pre-oxidation at higher temperatures in either air or N2-9%H2-1%H2O. Conversely, the oxidation rate increased when the alloy grain size was increased by heat-treating in H2 (pO2 ∼ 10−21 atm). In all cases the scale formed on Crofer 22 APU consisted of an outer (Mn,Cr)3O4 layer, an inner Cr2O3 layer and sub-scale MnCr2O4 nodules that preferentially formed at alloy grain boundaries.