Effects of CeO₂ on Melting Temperature, Viscosity, and Structure of CaF₂-bearing and B₂O₃-containing Mold Fluxes for Casting Rare Earth Alloy Heavy Rail Steels

Abstract

Rare earth have been widely used in the heavy rail steels to improve the impact toughness, yield strength, and high-temperature plasticity by deforming inclusions and refining grains. However, amounts of rare earth oxides with high melting temperatures can be generated and enter the mold fluxes, which has a significant influence on the lubrication and the heat transfer capability of mold fluxes and even the smooth of the continuous casting process. Thus in this work, effects of different CeO₂ contents on melting temperature, viscosity, and structure of the CaF₂-bearing mold fluxes and the B₂O₃-containing mold fluxes for casting the rare earth alloy heavy rail steels were investigated systemically. Besides, the mechanisms of the viscosity and structure were discussed. Results show that CeO₂ increases the melting temperature and decreases the viscosity at high temperature of both two mold fluxes. The break temperature of the CaF₂-bearing mold fluxes increases heavily with the addition of CeO₂. Analyses of Raman spectra and the ¹¹B magic angle spinning nuclear magnetic resonance spectra (¹¹B MAS NMR) show that CeO₂ enhances the de-polymerization of the network structure of two mold fluxes, leading to the decrease of viscosity at each temperature.