The mechanism of high temperature aqueous corrosion of steel

A new model is presented which describes the growth of the duplex layers of Fe3O4 on mild steel in high temperature, deoxygenated, neutral or alkaline aqueous solutions. It is shown that the layers grow by the ingress of water along oxide micropores to the metal-oxide interface and by the rate-limiting outward diffusion of Fe ions along oxide grain boundaries. The new model accounts for the observed temperature-dependence and pH-dependence of the corrosion, the morphology of inner and outer layer crystallites, the segregation of alloying elements, and the location of hydrogen evolution. The model can also be generalized to other steels and alloys. © 1989.