Abstract: The crystallization properties of CaO-Al₂O₃-based mold fluxes with different values of w(CaO)/w(Al₂O₃) were studied by using single hot thermocouple technique(SHTT) and scanning electron microscope and energy dispersive spectrometer(SEM-EDS). The results showed that the crystalline phases were LiAlO₂ and CaO·Al₂O₃ with a lower w(CaO)/w(Al₂O₃). They were formed due to the charge compensation of Li⁺ions and Ca²⁺ ions to aluminum tetrahedral structure with high polymerization degree. Li⁺ions were preferentially involved， and LiAlO₂ preferentially precipitated. With higher w(CaO)/w(Al₂O₃)， the crystalline phase was transformed into LiAlO₂ and 3CaO·Al₂O₃. The reason for the change was that the relative mass fraction of CaO was increased， accordingly， the degree of polymerization of the mold flux was decreased and 3CaO·Al₂O₃ was formed and precipitated due to the combination of Ca²⁺ ions and low-polymerization tetrahedral structural unit Q². As the w(CaO)/w(Al₂O₃) was increased from 1.13 to 1.82， the crystallization ability was first weakened and then increased. The crystallization ability was the weakest and the strongest when the w(CaO)/w(Al₂O₃) was 1.50 and 1.82， respectively.

Key words: CaO-Al₂O₃-based mold flux; crystallization temperature; crystalline phase; melt structure; SHTT(single hot thermocouple technique)