Scale formation mechanisms of martensitic steels in high CO2/H2O-containing gases simulating oxyfuel environments

• Published in: Materials at high temperatures Vol. 26; no. 1; pp. 63 - 72
• Main Authors: Pirón Abellán, J., Olszewski, T., Penkalla, H.J., Meier, G.H., Singheiser, L., Quadakkers, W.J.
• Format: Journal Article
• Language: English
• Published: Leeds Taylor & Francis 01.03.2009; Taylor & Francis Ltd
• Subjects: Carbon dioxide; Chromium; Chromium iron; Chromium steels; Martensitic stainless steels; martensitic steels; Oxides; oxyfuel power plants; Scale (corrosion); scale formation mechanisms; Steels; Vapour
• ISSN: 0960-3409; 1878-6413
• DOI: 10.3184/096034009X438185

In oxyfuel power plants, metallic components will be exposed to service environments containing high amounts of CO 2 and water vapour. Therefore, the oxidation behaviour of a number of martensitic 9-12%Cr steels in a model gas mixture containing 70% CO 2 -30% H 2 O was studied in the temperature range 550-700°C. The results were compared with the behaviour in air, Ar-CO 2 and Ar-H 2 O. It was found that in the CO 2 - and/or H 2 O-rich gases, the mentioned steels tended to form iron-rich oxide scales with significantly higher growth rates than the Cr-rich surface scales formed during air exposure. The iron-rich scales were formed as a result of a decreased flux of chromium in the bulk alloy toward the surface because of enhanced internal oxidation of chromium in the H 2 O-containing gases and carbide formation in the CO 2 -rich gases. Additionally, the presence of water vapour in the exposure atmosphere led to buckling of the outer haematite layer, apparently as a result of compressive oxide growth stresses. The Fe-base oxide scales formed in CO 2 (-H 2 O)-rich gases appeared to be permeable to CO 2 molecules resulting in substantial carburization of the steel.