Role of B2O3 on structure and shear-thinning property in CaO–SiO2–Na2O-based mold fluxes

Abstract

Most traditional mold fluxes are Newtonian fluids, and their constant viscosity has certain limitations in continuous casting. A new non-Newtonian fluid mold flux with shear-thinning behavior, i.e., a mold flux with a relatively high viscosity at lower shear rates and a relatively low viscosity at higher shear rates, is required to satisfy the mold-flux performance requirements for high-speed continuous casting. The addition of a certain amount of B2O3 to a CaO–SiO2–Na2O-based mold flux can result in a shear-thinning property. To obtain an improved understanding of the mechanism of this characteristic, a molecular-dynamics simulation method was used to study the microstructural changes of the mold flux. Structural changes of mold-flux samples were analyzed and verified by Raman spectroscopy. The results of the two methods were almost the same, both resulted from the addition of B2O3 and changed the microstructure and degree of polymerization of the mold flux, which resulted in the shear-thinning property of the mold flux. This non-Newtonian fluid mold flux was used in square-billet casting tests, and the quality of the slab was improved effectively.

Keywords

• mold flux
• non-newtonian fluid
• viscosity
• degree of polymerization
• shear-thinning