Corrosion of 9-12Cr ferritic-martensitic steels in high-temperature CO₂

The high temperature corrosion behavior of two 9Cr and 12Cr ferritic-martensitic steel grades was studied under CO₂ pressures varying from 1 to 250 bar for exposure times up to 8000 h. No 'breakaway' oxidation was observed. 9Cr steel grades suffered from fast parabolic uniform oxidation and fast carburization. Increasing CO₂ pressure had very little effect on the oxidation rate but increased the carburization rate. The corrosion behavior of both 12Cr steel grades differed and might be influenced by gas composition, minor elements or surface finish. A corrosion mechanism coupling oxidation and carburization is proposed. (authors)