Heat transfer across mold flux film in mold during initial solidification in continuous casting of steel

Abstract

Analysis of heat transfer near the meniscus in mold for continuous casting of steel has been carried out by taking into account conductive and radiative thermal resistances of infiltrated mold flux film and thermal resistance at the copper mold/solidifying mold flux film interface. Mold fluxes in commercial use for casting low and medium carbon steel are selected for this study. Thermal conductivities, absorption coefficients and interfacial thermal resistances of these fluxes have been determined in our previous work by laser flash method, high temperature cell FTIR test and contacting thermal resistance test, respectively. Calculation with these data shows that the heat transfer is strongly influenced by the interfacial thermal resistance. Slow cooling required for casting surface crack sensitive medium carbon peritectic steel slabs can be achieved by making the interfacial thermal resistance high, which is attainable by use of basic mold fluxes with high rate of crystallization. A flux film thicker than 0.25 mm for the low carbon steel or 0.4 mm for the medium carbon steel is also found to be a requisite to prevent the occurrence of longitudinal surface cracks. Reasonably high interfacial thermal resistance and a proper flux film thickness are essential to reduce the surface defects and to increase the speed of continuous casting of these steel slabs.