Scale formation mechanisms of martensitic steels in high CO{sub 2}/H{sub 2}O-containing gases simulating oxyfuel environments
- KFA Julich GmbH, Julich (Germany)
In oxyfuel power plants, metallic components will be exposed to service environments containing high amounts of CO{sub 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{sub 2}-30% H{sub 2}O was studied in the temperature range 550-700{sup o}C. The results were compared with the behaviour in air, Ar-CO{sub 2} and Ar-H{sub 2}O. It was found that in the CO{sub 2}- and/or H{sub 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{sub 2}O-containing gases and carbide formation in the CO{sub 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{sub 2}(-H{sub 2}O)-rich gases appeared to be permeable to CO{sub 2} molecules resulting in substantial carburization of the steel.
- OSTI ID:
- 21197972
- Journal Information:
- Materials at High Temperatures, Vol. 26, Issue 1; ISSN 0960-3409
- Country of Publication:
- United States
- Language:
- English
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