Effect of thermal cycling and phase transformations on chemical life of ferritic stainless steels

Journal article, 2026

Thin foils (0.3 mm thick) of ferritic stainless steels Crofer 22 APU and Crofer 22 H typically used for SOFC/SOEC applications were isothermally and discontinuously oxidized in air for up to 1000 h at 1000 °C. Both steel grades suffered from breakaway oxidation, Crofer 22 APU failing faster (70 h) than Crofer 22 H (700 h). Counterintuitively, isothermal exposure of Crofer 22 APU resulted in a more severe corrosion attack compared to discontinuous exposures with intermediate cooling steps. In contrast, Crofer 22 H was not affected by the thermal history of exposure. Breakaway oxidation of both steel grades is related to the α-to-γ transformation occurring above 900 °C. Crofer 22 H is less susceptible to austenitization.