Premature breakaway oxidation of ferritic stainless steels triggered by austenitization

Journal article, 2025

Thin foils (0.2-0.3 mm thick) of commercially available ferritic stainless steels Crofer 22 APU and Crofer 22 H have been oxidized in air for up to 2000 hat 900, 950, 1000, and 1050 degrees C. Both steel grades suffered from premature breakaway oxidation, despite the remnant Cr content in the foils being 18-20 wt% at the oxide-metal interface. Crofer 22 APU was found to be more susceptible to breakaway oxidation compared to Crofer 22 H. The classical lifetime prediction tools systematically overestimated the time to breakaway. Premature breakaway oxidation above 900 degrees C is demonstrated to be triggered by austenitization (the alpha-to-gamma transformation in the Fe-Cr system) occurring in the Cr-depleted corners and edges of the foils. A novel lifetime model accounting for austenitization and geometrical constraints was introduced and validated.