Rheological and Wetting Characteristics of Aluminate-Based Mold Flux for Low-Density Steel Continuous Casting and Their Correlation with the Ionic Structure Under Different (CaO + BaO)/Al2O3 Mass Ratios and B2O3 Substitution for SiO2
摘要
This work investigated the structure, properties and wetting characteristics of CaO–Al2O3-based mold fluxes for low-density steel continuous casting under different (CaO + BaO)/Al2O3 mass ratios and B2O3 substitution for SiO2. The results showed that as (CaO + BaO)/Al2O3 mass ratio increased from 0.87 to 2.11 and SiO2 was substituted by B2O3 within the range of 10 wt pct, the softening temperature, melting temperature and fluidity temperature decreased first and then increased. The break temperature continued to decrease, dropping from 1322 °C to 1165 °C and from 1280 °C to 1180 °C, respectively. The variations in viscosity and activation energy for viscous flow were in the same trend as the changes in melting characteristics. Structural analysis revealed that as the (CaO + BaO)/Al2O3 mass ratio increased, the competitive effect between the depolymerization role of O2− released by CaO and BaO and the structural roles of Ca2+ and Ba2+ caused the abnormal changes in viscosity. Also, Ba2+ gradually replaced Ca2+ to play the role of charge compensation on [AlO4]-tetrahedron. More Ca2+ charge balanced the negative charges of anion groups, maintaining electrical neutrality. As a result, the precipitated amount of Ca12Al14O32F2 phase decreased, and CaO phase began to form. As B2O3 gradually replaced SiO2, the Al–O–Si bond decreased and the Al–O–Al bond decreased first and then increased. For borate structure, the AlIV–O–BIII bond first increased and then decreased, while the AlIV–O–BIV bond, BO3–BO4 and BO3–BO3 structures all increased. Furthermore, the relationship between contact angle and melt structure under different (CaO + BaO)/Al2O3 mass ratios and substitution of SiO2 by B2O3 was clarified.