12th International Conference on Zinc & Zinc Alloy Coated Steel Sheet - GALVATECH 2021

One of the challenges on the development of new steel products is the possibility to predict or control surface behaviour through-process. The lack of prediction, together with the difficulty on simulating the behaviour of the surface in pilot processing, lead to the evaluation of the product after costly industrial trials. Therefore, knowledge on the kinetics of oxide formation on steels is of significant importance for the steel industry. Hot rolling is one of the steps in steel making during which oxidation plays an important role. This oxidation can enormously affect the further stages (e.g. coiling). The formation of a Wüstite scale occurs, when a hot iron sheet is in an atmosphere with oxygen partial pressure (pO2) above that for Wüstite formation, e.g. above 1.2 × 10^(-15) atm at 1273 K. This kind of oxidation has been studied extensively in a mixture of oxidants as CO2 and H2O as well as reductants CO and H2 for long times. The aim of this study is to investigate the kinetics of Wüstite layer formation on pure iron in short times (less than one minute). To predict surface oxidation for short times, a model is developed for the kinetics of Wüstite formation on pure iron in CO2 + CO and H2O + H2 gas mixtures as a function of temperature and gas composition. The thermodynamic and kinetic data needed for the calculations, are obtained using the FactSage and Thermo-Calc database packages. The model is compared with a set of experiments carried out using Thermal Gravimetric Analysis (TGA) and also with recently reported experimental results from literature. It is shown that the initial oxidation of pure iron in such oxidizing atmosphere follows a linear kinetics that is controlled by the surface reactions at the gas-scale interface. A set of chemisorption reactions of oxidant molecules are suggested as the rate controlling reactions. The experimental findings on the oxidation of iron will be compared with the model calculations.