| Summary: | For many years, commercial 9Cr-1Mo steels have been used for components in the UK advanced gas cooled reactors operated by EDF Energy. The selection of 9Cr-1Mo steel for power plant applications is based on its relatively low cost, resistance to high temperature oxidation and excellent high temperature creep strength. However, degradation occurs in service due to thermal aging and exposure to the CO2-based coolant gas. Under some circumstances, rapid oxidation can occur, known as “breakaway oxidation”. The degradation of the mechanical and corrosion properties has prompted study of the mechanisms of concurrent oxidation and carburisation in a high-temperature CO2-based atmosphere. Here, experimental finned tube samples with ferritic and martensitic microstructures exposed to simulated in-service environments have been analysed using several techniques to understand the triggers of breakaway oxidation.
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