Modelling the boundary conditions for thermo-mechanical processing - oxide scale behaviour and composition effects

It is known that better understanding of events at the tool-workpiece interface will lead to better definition of the boundary conditions for the process models. The deformation of the oxide scale on the surface of steel being hot worked contributes to the interface complexity. This scale has a complicated microstructure, and can deform or fracture. In hot rolling, the deformation of the scale begins before the steel makes contact with the roll, under the influence of a tensile stress as the roll draws the metal into the roll gap. Tension tests under controlled conditions have been used to simulate this initial deformation and have revealed ductile and brittle behaviour, according to the operating conditions. This behaviour is also very sensitive to small changes in the chemical composition of the underlying steel. This is illustrated for two low-carbon steels. The laboratory observations art: complemented by finite element modelling of the tensile deformation, which is capable of reproducing both ductile and brittle behaviour of the oxide scale with the same model. The model is adjusted to mimic the effect of changing the chemical composition of the steel.