Mechanisms of steam oxidation in high strength martensitic steels

The oxidation resistance of 9–12% chromium steels in steam-containing environments simulating the service conditions of steam power plant has been investigated for exposure times ranging from 1 h up to 10,000 h. The time-dependent changes in the complex structures of the scales were determined using optical microscopy. Different oxidation mechanisms were observed for different temperature regimes, exposure times and exposure conditions. The cracking and spallation of scales was correlated with the type, morphology and growth of pores and voids in the scale and could be influenced by the steel microstructure. For some steels, the steam oxidation resistance increased with increasing exposure temperature. The oxidation rates only slightly depend on the exact water vapour content in the test gas but can be affected by the gas flow rates.