Modelling of Thermal History and Microstructural Evolution On Runout Table of Hot Strip Mill

Accelerated cooling or direct quenching of steel after thermo-mechanical treatment plays an important role in determining steel properties. Consequently, the runout table of a hot strip mill is a valuable metallurgical tool for achieving desired microstructures. Accurate cooling control is essential in the production of the latest strip steels with ultra high strength and high toughness combined with good weldability and flatness. Accurate control of the cooling path and final microstructure requires the use of physical and numerical simulation.

In the present study, a numerical model of runout table cooling has been developed and validated against hot strip mill data. The unsteady temperature and phase transformation behavior was simulated using a finite volume method and by considering a two-dimensional piece of hot rolled strip, which was subsequently exposed to different mechanisms of heat transfer according to layout of the given runout table. The parameters of the model were determined with the help of an appropriate testing programme and a set of test coils. The Levenberg-Marquardt algorithm was used in the adaptation method. The validity of the proposed numerical model was examined by simulating industrial production cooling schedules used in the production of steel strips with yield strengths in the range 900-1200 MPa. The results reveal that the predicted temperatures and microstructures for different thicknesses and velocities are in good agreement with plant operational data.