Effect of SiO₂ on the Crystallization Behaviors and In-Mold Performance of CaF₂-CaO-Al₂O₃ Slags for Drawing-Ingot-Type Electroslag Remelting

The crystallization characteristics of CaF₂-CaO-Al₂O₃ slags with varying amounts of SiO₂ were experimentally studied. The effects of slag crystallization behaviors on the horizontal heat transfer and lubrication performance in drawing-ingot-type electroslag remelting (ESR) were also evaluated in terms of as-cast ingots surface quality and drawing-ingot operation. The results show that increasing SiO₂ addition from 0 to 6.8 mass pct strongly suppresses the crystallization of ESR type CaF₂-CaO-Al₂O₃ slags. The crystallization temperature of the studied slags decreases with the increase in SiO₂ addition. The liquidus temperatures of the slags also show a decreasing trend with increasing SiO₂ content. In CaF₂-CaO-Al₂O₃-(SiO₂) slags, faceted 11CaO·7Al₂O₃·CaF₂ crystals precipitate first during continuous cooling of the slag melts, followed by the formation of CaF₂ at lower temperatures. 11CaO·7Al₂O₃·CaF₂ was confirmed to be the dominant crystalline phase in the studied slags. CaF₂-CaO-Al₂O₃ slags with a small amount of SiO₂ addition are favorable for providing sound lubrication and horizontal heat transfer in mold for drawing-ingot-type ESR, which consequently bring the improvement in the surface quality of ESR ingot and drawing-ingot operating practice as demonstrated by plant trials.