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

Abstract 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 N 2 -9%H 2 -1%H 2 O. Conversely, the oxidation rate increased when the alloy grain size was increased by heat-treating in H 2 (pO 2  ∼ 10 −21  atm). In all cases the scale formed on Crofer 22 APU consisted of an outer (Mn,Cr) 3 O 4 layer, an inner Cr 2 O 3 layer and sub-scale MnCr 2 O 4 nodules that preferentially formed at alloy grain boundaries.