Crystallization Characteristics and In-Mold Performance of Electroslag Remelting-Type TiO₂-Bearing Slag

The non-isothermal crystallization characteristics of the electroslag remelting (ESR)-type TiO₂-bearing slag were studied. The effect of crystallization characteristics of the slag on the in-mold performance was verified by ESR pilot trials operating in a static mode. The results showed that increasing TiO₂ content decreased the crystallization temperature and liquidus temperature of the slag and suppressed the crystallization tendency of the slag. There is no change in the types of the crystalline phases in the slag with different TiO₂ contents during cooling, i.e., 11CaO·7Al₂O₃·CaF₂, CaTiO₃, and CaF₂. The sequence of crystal precipitation during cooling was 11CaO·7Al₂O₃·CaF₂ to CaTiO₃, and then CaF₂ with increasing TiO₂ content from 4.2 to 12.6 mass pct. With adding 16.8 mass pct TiO₂ in the slag, the precipitation of 11CaO·7Al₂O₃·CaF₂ and CaTiO₃ took place simultaneously, followed by CaF₂. With the increase in the TiO₂ content from 4.2 to 16.8 mass pct in the slag, the dominant crystalline phase changed from 11CaO·7Al₂O₃·CaF₂ to CaTiO₃. The morphology of 11CaO·7Al₂O₃·CaF₂ and CaTiO₃ changed from faceted and bonelike to elliptically faceted and blocky, respectively. The morphology of CaF₂ were spherical in all cases, irrespective of TiO₂ contents in the slag. The decrease in the crystallization tendency of the slag with increasing TiO₂ contents was attributed to the decrease in the activity of CaO in the slag. The increasing of TiO₂ content in the slag are favorable for providing thin slag skin and stable heat flux across the slag skin, which improved the surface quality of the as-cast ESR ingot as demonstrated by ESR pilot trials operating in a static mode.