Modelling of dynamic scale layer growth considering temperature, time and alloying elements

Abstract: During hot forming of steel oxide scaling occurs at higher temperatures caused by reactions with oxide containing atmospheres. Three characteristic iron oxides exist for steel at temperatures above 570°C: Wustite (FeO), magnetite (Fe3O4) and hematite (Fe2O3). Scale layer formation is influenced by various process parameters, such as temperature, process time and furnace atmosphere. Additionally, the base material with different alloying elements (e.g. C, Cr, Si and Ni) also affects the scale layer formation. Therefor oxide scales are very difficult to handle in the entire manufacturing process. The aim of this work is to examine and evaluate the influence of temperature, time and the alloying elements C and Cr in association with the layer growth, layer composition and thermophysical properties for scale layers. Based on the achieved correlations, a model is developed, which is able to predict the scale formation and scale properties, depending on temperature, time and alloying elements. With rising temperature and time increasing layer thicknesses were observed. Further, the additional Cr ensured lower layer thicknesses compared to the unalloyed steels. The iron oxide distribution changed with rising temperature to higher oxide containing phases like magnetite and hematite. The mathematical model, developed based on this results, is able to calculate the resulting layer structure, thickness and thermophysical properties depending on temperature, time and chemical composition of the material.