A Novel Phase Transformation Model based on Gibbs’ Free Enthalpy and the Stefan Equation improves Material Properties of Hot Rolled Products

摘要

A novel phase transformation model has been developed for application within process control of thecooling section and the finishing mill to predict and control the material properties. It is based on a full thermodynamic description, using the concept of Gibbs’ Free Enthalpy and the diffusion within austenite based on Stefan’s equation. The model is able to predict an equilibrium diagram and a TTT diagram (arbitrary temperature course) in dependence of the steel chemistry. It furthermore is able to compute the phase fractions of austenite, ferrite, cementite and pearlite and the distribution of the strip temperature along the entire strip in real time, when integrated with Fourier’s heat equation. Due to this novel cooling model, powerful new features of the cooling automation system can be used during steel production to control material properties. The cooling automation system is taken into operation at Hoesch Hohenlimburg now.