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

Abstract

It is known that better understanding of events at the tool-workpieceinterface will lead to better definition of the boundary conditions for theprocess models. The deformation of the oxide scale on the surface of steelbeing hot worked contributes to the interface complexity. This scale has acomplicated microstructure, and can deform or fracture. In hot rolling, thedeformation of the scale begins before the steel makes contact with theroll, under the influence of a tensile stress as the roll draws the metalinto the roll gap. Tension tests under controlled conditions have been usedto simulate this initial deformation and have revealed ductile and brittlebehaviour, according to the operating conditions. This behaviour is alsovery sensitive to small changes in the chemical composition of theunderlying steel. This is illustrated for two low-carbon steels. Thelaboratory observations are complemented by finite element modelling of thetensile deformation, which is capable of reproducing both ductile andbrittle behaviour of the oxide scale with the same model. The model isadjusted to mimic the effect of changing the chemical composition of thesteel.