Extended Model for Prediction of Transition from Internal to External Oxidation in Steels: Comparison between Analytical/Semi-Analytical and Numerical Approaches

Abstract

The aim of this paper is to present a model that predicts the transition from internal to external oxidation. This variant is based on the simultaneous resolution of the diffusion equations and the equilibrium equation that stems from the assumption of the local instantaneous thermodynamic equilibrium. It accounts for the possible formation of large precipitates fractions that may act as diffusion barriers. This effect is modeled by introducing a dependence of the diffusion coefficients upon the mass fraction of precipitates. As a counterpart, it is generally impossible to solve the non-linear equations of the model analytically. Thus, a semi-analytical and a finite elements models are presented.