In the process of continuous casting, especially high-speed continuous casting, the inflow state of the mold flux is particularly important. The fluxing agent is one of the most important factors affecting the flow state. The influence of the typical fluxing agent B₂O₃ on the viscous characteristics and melt structure of the fluorine-free CaO-SiO₂-M₂O (M = Li, Na) system was analyzed. The following conclusions were drawn. In the CaO-SiO₂-Na₂O slags, with the increasing addition of B₂O₃, the viscosity, breaking temperature, and polymerization degree of the slag show a gradually decreasing trend. When the mass fraction of B₂O₃ increased from 0 to 10%, the increase in two-dimensional [BO₃] structural units played a dominant role. When the mass fraction of B₂O₃ reached 15%, the network was affected by the increase in [BO₃] and the low-polymerized [SiO₄] tetrahedrons. The CaO-SiO₂-Li₂O slag system had a lower breaking temperature due to the formation of phases such as Li₂O·2B₂O₃, of a low melting temperature. The initial degree of depolymerization of the network was high. Upon increasing the addition of B₂O₃, the relative proportion of the network modifier structural units significantly increased, resulting in the enhanced instability of the network structure. As a result, the effect of [SiO₄]-polymerization was stronger than that of [BO₃]-depolymerization in maintaining the stability of the network structure.

For continuous casting of strong reducing steels, the low-reactive aluminate-based mold flux consisting of CaO-SiO₂-Al₂O₃-CaF₂-Li₂O-B₂O₃-Na₂O with low SiO₂ content was designed. The correlation between the melt structure under high temperature and the crystallization phases during the cooling process and the change of viscosity was analyzed. The following conclusions were obtained. The polymerization degree of the mold flux consistently decreased as the w(CaO)/w(Al₂O₃) ratio increased from 0.93 to 1.65. Due to melt structure depolymerization, the viscosity at 1300 °C dropped from 0.132 Pa·s to 0.054 Pa·s. As the w(CaO)/w(Al₂O₃) ratio increases near the breaking temperature, the crystalline phases in the mold flux transition from LiAlO₂ to Ca₂Al₂SiO₇, and finally to a combination of Ca₁₂Al₁₄O₃₂F₂ and LiAlO₂. The rapid viscosity increase at the breaking temperature was primarily due to the precipitation of these phases. Furthermore, influenced by the changes in crystallization tendency and crystalline phase precipitation, the breaking temperature first decreased and then increased. Increasing the Li₂O mass fraction from 5% to 9% led to a decrease in the polymerization degree of the mold flux. Due to the depolymerizing impact of Li₂O on the slag network, the mold flux viscosity at 1300 °C decreased from 0.102 Pa·s to 0.047 Pa·s. The breaking temperature of the mold flux rose notably with a higher Li₂O mass fraction. At the breaking temperature, the crystalline phases in the mold flux transition from Ca₂Al₂SiO₇ to a combination of LiAlO₂ and Ca₁₂Al₁₄O₃₂F₂. The precipitation of these phases at the breaking temperature directly caused a rapid increase in viscosity. The results systematically reveal the coupling mechanism between melt structure, crystalline phase evolution, and viscosity variation of low-SiO₂ aluminate-based mold flux, which provides an important theoretical basis for composition design and performance regulation of mold fluxes for high-aluminum steel continuous casting.

The surface tension evaluation model of the Fe-based Cr–Ni–Ce–O–N heat-resistant alloy system was built, and the model shows good reproducibility. Calculations showed that nitrogen and oxygen are surface-active elements. Cerium also can work as a surface-active element with a low content of nitrogen and oxygen. The contents of O, Ce and N on the surface were higher than those in the bulk. The surface tension of heat-resistant steel in the refining process decreases due to blowing nitrogen. The effect of oxygen to reduce the surface tension is more significant. The decrease of the surface tension and periodical change of the interfacial properties caused by the ‘stirring’ effect of oxygen were helpful to promote the decarburisation process. The surface tension of the molten heat-resistant steel can stay constant with feeding Ce-wire in the Ladle Furnace (LF) refining process, which is helpful to form a stable reaction interface between the refining slag and the melt surface.