Characterisation and modelling of the damage and delamination behaviour of oxide scale layers in hot bulk forming

Abstract In hot forming processes of steel, oxide scale layers are formed in dependence of the occurring process conditions. As remaining oxide scale can weaken the formed workpiece, it has to be removed at the end of the process. Through this, the oxide scale formation can lead to a mass loss of up to 3% in addition to influencing the forming process for example by affecting the friction conditions or increasing the die wear. However, oxide scale layers can protect against further oxidation and limit the mass loss as long as they are not damaged or separated from the workpiece, for example through cracks or delamination. In order to evaluate the resulting forming process in dependence of the oxide scale layer, numerical simulations can be applied. For a precise numerical description of a forming process using a finite element simulation, it is necessary to model the delamination and damage behaviour of the oxide layer. This paper presents a characterisation and modelling approach to describe the delamination and damage behaviour based on the occurring stresses in dependence of the temperature. The results of the experimental study indicate that the investigated oxide scale layers were more sensitive towards delamination than crack initiation. The derived models allowed to numerically recreate the experimental tests.