Modelling the Spalling of Oxide Scales During Hot Rolling of Steel Strip

Production of hot rolled steel strip is carried out at temperatures at which oxidation is prone to occur. The oxide crust is subjected to stresses that are originated while growing or are due to the difference between the thermal expansion coefficients of steel and oxide. It is considered that the oxide crust will be in tension when the temperature at the surface of the steel increases and in compression when it decreases. These stresses may cause cracking, buckling and spalling of the oxide. Oxidation to hematite occurs very rapidly once the crust is detached from the surface of the steel, and, in some cases oxide dust clouds will be formed. A model was developed to predict the magnitude and nature of the stresses within the oxide layer considering the temperature changes that take place while the material is being rolled. The model predicts that the oxide crust will deform when compressed and may cause its spalling and, once this occurs it will be expected to form oxide dust clouds.