Crystallization Characteristics and In-Mold Performance of Electroslag Remelting-Type TiO2-Bearing Slag
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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.
The authors are sincerely grateful to Professor Jung-wook Cho, Pohang University of Science and Technology, for his help in using the FactSage software. The financial support by the National Natural Science Foundation of China (Grant Nos. 51774225, 51874030, and 51874026) and the Fundamental Research Funds for the Central Universities (Grant No. FRF-TP-18-004A3) is greatly acknowledged.
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