Published Paper Details:

P91 ferritic-martensitic steel is widely used in fossil-fires power plants because of its high creep strength and oxidation resistance at elevated temperatures. However, transient overheating above the design temperature can accelerate oxidation, damage the protective oxide scale, and reduce component reliability. In this study, the isothermal oxidation of P91 steel under short-term overheating was investigated in dry air at 600? and 800? for up to 350 h using weight gain measurements, SEM, cross-sectional analysis, and EDS. The results showed that oxidation increased with both exposure time and temperature, with temperature having the stronger effect. At 600?, P91 steel formed a thin, compact, and adherent oxide scale with low weight gain. In contrast, at 800?, the weight gain increased markedly and a much thicker oxide scale developed, with localized cracking and partial delamination. Cross-sectional SEM confirmed faster oxide growth at the higher temperature, while EDS mapping showed a duplex structure with an Fe-rich outer layer and a Cr-rich inner layer. The chromium-rich inner layer was protective at 600?, but its effectiveness decreased at 800? due to rapid oxide growth and enhanced diffusion of oxygen and iron. Overall, short-term overheating significantly reduces the oxidation of P91 steel by accelerating oxide growth and weaking the protective chromium-rich layer. These findings help explain the oxidation behavior of P91 steel during transient overheating in power plant service.