The ability to control the mechanical properties of hot rolled steel strip depends strongly on the knowledge of the metallurgical processes taking place during production. On the ran-out table of a hot strip mill, the most important metallurgical process is the austenite transformation into phases like ferrite, pearlite, bainite and martensite. The kinetics of this process, and with that the final microstructure, can be controlled by applying controlled cooling. In the last decade, Corus, formerly Koninklijke Hoogovens, developed a physics-based control model for the run-out cooling table of the hot-strip mill in IJmuiden. For the development of the physical model describing the kinetics of the austenite decomposition, Hoogovens entered into a close cooperation with the laboratory of Materials Science of the Delft University of Technology. This collaboration has proven its value, as will be outlined in this paper.