Numerical Simulation of Heat Transfer Process under Ultra Fast Cooling for Hot Strip

摘要

To obtain the needed crystallographic texture and microstructure, different from the traditional controlled cooling technology, the new controlled cooling technology orientate towards control of the phase transformation on the run-out tables based upon continuous cooling transformation (CCT) diagrams. In this respect the development of new controlled cooling technology is needed. In this paper, a cooling system for the products of hot flat rolling, UFC (ultra fast cooling system) which allows the cooling rate up to 300°C/s on thin hot strip, was introduced. This new cooling technology which may generated a range of microstructures from the same chemical compositiorfby changing the intermediate and cooling temperatures can be applied for developing ultra fine grained steels or the high strength steels. The convective heat transfer coefficient is the key to the cooling rate of the hot strip. The ultra fast cooling of the hot strip was modeled by considering the cooling of a small piece of strip. The convective heat transfer coefficient which allows the cooling rate up to 300°C/s on thin hot strip was given by finite difference method, and the temperature field under ultra fast cooling (UFC) was simulated by the finite element method. The results of the numerical simulation shows that the temperature gradient in thickness would be an great important factor for the on-line application of the UFC on the hot strip runout.