Mechanism of the Formation of the Oxidation Layers of T91 Steel Tube Under the High Temperature Water Vapour

In order to research the mechanism of the formation of the oxidation layers of T91 steel under the high temperature water vapour,the profile morphololgies of rust scale of the inner wall of T91 boiler re-heater was observed by the optical microscope and scanning electron microscope,and the phase structure of the oxide layer was also analyzed by X-ray diffraction.The results showed that under high-temperature and high-pressure water vapour the inner oxide layer of T91 steel tube is the very thin layer of CrFe_2O_4(which contains 37% cation vacanies),which is a single-phase,non-grain boundary and non-crystal microstructure;The medial layer is the thick,single-phase layer CrFe_2O_4 which consists of the lower fine equiaxed crystal structure and the upper coarse columnar crystal microstructure;the outer layer is Fe_3O_4-Fe_2O_3 which consists of the lower tine equiased crystal and the upper coarse columnar crystal microstructure.