Exploration of Li₂O reduction by mold flux for high quality low carbon steel slab continuous casting

Li₂O can effectively improve the melting and flow properties of continuous casting mold fluxes, and is commonly used as an important constituent in mold flues in high-quality low-carbon steel slab continuous casting. However, in the past two years, due to strong downstream demand, the price of lithium carbonate has continued to rise, leading to the increased production cost of continuous casting. Firstly, laboratory research was carried out, focusing on the influence of Li₂O on the viscosity and melting temperature with different basicity; Then four industrial tests were carried out in stages, and the evaluation indicators included the curves of the mold copper plate thermocouple temperature and friction force, the consumption of steel slag per ton, and the surface quality of the strand. The results show that in the range of bascity from 0.65 to 1.25, with the increase of Li₂O content, both the melting point and viscosity show a downward trend, and the viscosity decreases significantly. In order to ensure smooth continuous casting and strand surface quality, it is necessary to adjust the content of Al₂O₃, Na₂O, and F^- in the fluxes while decreasing Li₂O, in order to achieve coordination of the melting and flowing properties of the fluxes and stability of the performance after absorbing Al₂O₃.The basicity of the optimized slag is 0.98, the viscosity is 0.26 Pa·s, and the melting point is 1 130 ℃, all of which are within the performance requirements of low-carbon steel mold flux. Compared with the optimized flux, the mass percent of Li₂O of the original mold flux was significantly decreased from 3.79% to 0.79%, and the mass percent of Na₂O was increased from 1.57% to 6.54%, the mass percent Al₂O₃ was decreased from 12.05% to 3.62%. Before and after use, the viscosity of the optimized slag in the high-temperature stage (1 200-1 300 ℃) shown in the viscosity- temperature curve basically coincides, and the transition temperature has increased. The operation of optimized flux is stable, the curves of the mold copper plate thermocouple temperature and friction force fluctuate smoothly, and the continuous casting strand and rolled sheet are free of defects related with mold fluxes. This study aims to reduce the production cost of continuous casting from the perspective of mold fluxes, and the research results have certain reference and promotion value.