Kinetics of Crystallization of Mold Flux for Middle Carbon Steel by Isothermal Heat Treatment

Abstract

Mold flux is widely used in continuous casting of steel. The heat transfer control in the mold is one of the important roles of mold flux. The mild cooling due to crystallization of mold flux is established for middle carbon steel, which has a high tendency for longitudinal cracking. However, the mechanism of crystallization has not well understood. Therefore, the kinetics of crystallization via glassy state has been analyzed in this study, using a commercial mold flux, which easily crystallizes.
Quenched mold flux was prepared and heat treated at some temperatures for various periods. After heat-treatment, the mold flux was analyzed by XRD to confirm the phase, glass or crystalline. The time for crystallization as a function of heat-treatment temperature was experimentally determined. Then the apparent activation energy for crystallization was estimated using Arrhenius plot. The calculated value is 193 kJ/mol and this may correspond to the activation energy for diffusion of some molecules or ions in a glassy state of mold flux.