Growth behavior of oxide scale formed on Cr-Mo steels in steam

The oxidation behavior of commercial carbon steel and Cr-Mo steels with Cr content lower than 12% in steam was studied. The oxidation behavior changed with temperature. Below 550 degrees C, the growth of the oxide scale in steam was slow, and no distinct effects of Cr-content on the growth rate were observed. Above 600 degrees C, the extremely thick oxide scale developed on the carbon steel due to the formation of FeO, while the growth rate of the oxide scale formed on Cr-Mo steels changed with the variation of Cr content in the steels. In higher Cr (ca. 12%Cr) containing steels, the belt-shaped Cr containing oxide scale was formed in the inner oxide layer. The diffusion of Fe through the oxide scale was controlled by the amount of Cr in the inner oxide layer. The high concentration of Cr in the inner oxide layer was found to be effective for retarding the growth of the oxide scale.