Scale Behaviour and Deformation Properties of Oxide Scale during Hot Rolling of Steel

This paper describes the possibilities for identifying temperature-dependent mechanical and thermo-physical properties of oxide scale components which are a necessary data input for a numerical simulation. Scale develops on steel surfaces in oxidising atmospheres above 570 C and influences the surface quality as well as the roughness of semi-finished products. The main components of oxide scale are wustite, magnetite, and hematite. Intermediate layers can be formed depending on the chemical composition of the basic material, which can be assigned at the rolled samples with the help of the optical microscopy. Hence, the mechanical properties and the metal forming relevant properties of the several oxide layers are very different. Owing to these differences the deformation behaviour of the inhomogeneous oxide scale also varies during hot rolling. With this new method is it possible to determine the pure properties of the several oxide scale layers independently from each other. Thereby, the influences of the raw material as well as the alloys are excluded. The pure powder allows to characterising the physical properties by applying compression tests with similar stress condition then during hot rolling. Additionally, the 3 piont-bending tests are conducted in order to describe the fracture toughness of the oxides. The results will be implemented in a new model, which consist of single layers with specific material properties. Based on the new knowledge the forming technology can be managed and controlled to minimise the scale cracks on the surface and thus the resulting roughness as well.