Crystallization Behaviors of CaF2–CaO–Al2O3–MgO–B2O3 Slag for Electroslag Remelting of B-Containing Rack Steel

Abstract

The crystallization behaviors of CaF₂–CaO–Al₂O₃–MgO–B₂O₃ slag for electroslag remelting of B-containing rack steel was investigated through a series of non-isothermal and isothermal crystallization experiments. The techniques employed for this determination included differential scanning calorimetry, X-ray diffraction, scanning electron microscopy-energy dispersive spectroscopy, and FactSage 8.2. The results indicated that an increase in B₂O₃ content suppressed the crystallization of CaF₂–CaO–Al₂O₃–MgO slag. The crystallization temperature decreased as the B₂O₃ content in the slag increased from 2 to 7 mass pct. In the slag containing 2 mass pct B₂O₃, spherical CaF₂ precipitates first, followed by reticulate Ca₁₂Al₁₄F₂O₃₂ phase. Increasing B₂O₃ addition promoted the formation of Ca₅(BO₃)₃F and calcium aluminate (Ca₁₂Al₁₄O₃₃ or CaAl₄O₇), and decreased the crystallization of Ca₁₂Al₁₄F₂O₃₂ phase. The crystallization sequence transformed into CaF₂ → CaAl₄O₇ → MgAl₂O₄ + Ca₅(BO₃)₃F in the case of 7 mass pct B₂O₃. B₂O₃ addition inhibits the crystallization of the dominated phase CaF₂, which would improving the lubrication and heat transfer performance of ESR-type CaF₂–CaO–Al₂O₃–MgO slags.