Isothermal and non-isothermal crystallization kinetics of mold fluxes used in continuous casting of steel : a review

Casting powders or mold fluxes, as they are more commonly known, are used in the continuous casting of steel to prevent the steel shell from sticking to the copper mold. The powders first melt and create a pool of liquid flux above the liquid steel in the mold, and then the liquid mold fluxes penetrate into the gap between water-cooled copper mold and steel shell, where crystallization of solid phases takes place as the temperatures gradually drop. It is important to understand the crystallization behavior of these mold fluxes used in the continuous casting of steel because the crystalline phase fraction in the slag films plays a crucial role in determining the horizontal heat flux during the casting process. In this work, the existing literature on the crystallization kinetics of conventional and fluoride-free mold fluxes used in the continuous casting of steel have been reviewed. The review has been divided into two main sections viz. the isothermal crystallization kinetics and non-isothermal crystallization kinetics. Under each of these sections, the three of the most widely used techniques for studying the crystallization kinetics have been included viz. thermoanalytical techniques such as Differential Scanning Calorimetry/ Differential Thermal Analysis (DSC/DTA), the Single and Double Hot Thermocouple Technique (SHTT and DHTT) and the Confocal Scanning Laser Microscopy (CSLM). For each of these techniques, the available literature related to the crystallization kinetics of mold fluxes have been summarized thereby encompassing a wide range of investigations comprising of both conventional and fluoride-free fluxes. Summaries have been included after each section with critical comments and insights by the authors. Finally, the relative merits and demerits of these methods vis-à-vis their application in studying the crystallization kinetics of mold fluxes have been discussed