Voestalpine-Schienen GmbH produces two types of heat treated rails for the highest demands in railroad traffic. Aside from the different modes of processing continuous cooling in the HSH process and isothermal transformation in the bainitic process the properties of quenching agents are different. Voestalpine-Schienen GmbH is planning to manufacture both types of rails with one single quenching agent. The cooling mechanism of aqueous polymer quenchants can be decisively influenced by the following process parameters: - the intensity of the flow of the quenchant onto the rail - the temperature of the quenchant - the concentration of the quenchant - addition of air into the quenchant and the amount of air added These influences were investigated in an earlier project (Metallurgie 06/01). Today quenchants are available which make a more abrupt cooling in a stable film boiling phase possible. The aim of this diploma thesis is the selection of an appropriate quenchant and the determination of the optimal process parameters for the manufacture of both pearlitic and bainitic rails in a stable film boiling phase.