Viscosity and Crystallization Behavior of F-free Mold Flux for Casting Medium Carbon Steels

Abstract

Viscosity and crystallization are essential properties to characterize the lubrication and heat transfer performances of mold flux. Therefore, in this paper, the viscosity and crystallization behaviors of conventional F-containing commercial mold flux and newly designed F-free mold fluxes were investigated by using rotating cylinder method and Single/Double Hot Thermocouple Technique (SHTT/DHTT). Results shows that the viscosities of designed F-free mold fluxes are close to the F-containing mold flux; and the crystallization temperatures of F-free mold fluxes increases with the increase of basicity and Na₂O/Li₂O content; while it decreases with the increase of cooling rate and the addition of B₂O₃. The final steady state structure of F-free mold fluxes during the DHTT tests shows it is composed of a major crystalline and a thin liquid layer (5.42–7.2%) without glass phase. The results of XRD indicate that the main crystalline phases formed in designed F-free mold fluxes were calcium borosilicate (Ca₁₁Si₄B₂O₂₂) and calcium magnesium silicate (Ca₁₄Mg₂(SiO₄)₈. Through the comprehensive comparison, the designed F-free mold fluxes flux Sample E (Basicity 1.15, Na₂O 7.92, Li₂O 1.97 and B₂O₃ 5.98) has the closest performances to the benchmark conventional mold flux Sample A.