New Mold Fluxes for Rare Earth Steel Continuous Casting—Composition Design and Property Analysis

Rare earth has been widely introduced in heat-resistant steel. However, excessive amounts of rare earth should be added due to the low yield rate, and the molten steel in the mold was highly reducible. Severe slag–metal interface reactions occurred when conventional mold fluxes were used. To restrain interfacial reactions during continuous casting of heat-resistant steel containing rare earth, a new method for designing mold flux was proposed, and different flux systems containing rare earth oxide were devised. The properties such as melting temperature, viscosity, and crystalline phase of the different mold fluxes were systematically investigated. Comparisons of properties between the new fluxes and the conventional mold fluxes were conducted. The results show that properties similar to those of the conventional mold flux could be obtained by adopting Li2O and B2O3 as fluxing agents in the newly designed system. The new mold flux with high content of CaO and Al2O3 had approximate properties with the conventional mold flux. Cerium oxide could not separate out in the continuous cooling process. The main crystalline phase was LiAlO2 in the new mold fluxes, which is different from the cuspidine (3CaO∙2SiO2∙CaF2) in the conventional mold flux. LiAlO2 can be a potential substitute for cuspidine. It was entirely feasible to devise and develop a new mold flux containing rare earth with a high content of CaO and Al2O3 for rare earth steel continuous casting by further optimizing its properties.