High Temperature Steam Oxidation of High Cr Ferritic Steels
Mitsutoshi Ueda, Toshio Maruyama
High temperature steam oxidation has been occurred inside the boiler tubes of the superheater and reheater in fossil fuel-fired power plants. Exfoliation of the scale formed by the steam oxidation sometimes makes troubles such as the blockage of the boiler tubes and the erosion of the turbine components. Recently, operating temperature and pressure has been improved due to achieve high efficiency. In Japan, steam conditions have been reached at the ultra super critical steam condition (883K/31.6MPa). These boiler tubes have been mainly made of iron-chromium ferritic and austenitic steels. Recently, Fe-Cr ferritic steels have been widely chosen from the advantages of low costs and low thermal expansion coefficients that close to the oxide scale formed on the alloy surface. But, steam oxidation behavior of the high Cr ferritic steels is not clarified. From 1990's, many researchers have started fundamental researches of the steam oxidation of high Cr ferritic steel, because it needed to clarify the scale formation and control the scale exfoliation.
In this paper, high temperature steam oxidation of high chromium ferritic steels are mentioned in the viewpoint of the microstructure evolution of the scale, the effect of Si addition, void formation and hydrogen permeation in the oxide scale.