Crystallization Characteristics and In-Mold Performance of Electroslag Remelting-Type TiO 2 -Bearing Slag
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ELECTROSLAG remelting (ESR) is a secondary refining technique used for the production of some varieties of high-grade specialty steels and alloys. Slag plays an important role in the ESR process. For example, (1) the slag refines the liquid metal such as by removal of harmful elements and nonmetallic inclusions,[1,2] (2) the slag reacts with liquid metal to adjust the compositions of the ingot,[3,4] and (3) the slag film plays a key role in controlling horizontal heat transfer in the mold and providing lubrication for drawing-ingot-type ESR,[5] which could provide a sound condition for the good surface quality of as-cast ingot.[6]
DINGLI ZHENG, JING LI, and CHENGBIN SHI are with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing (USTB), Beijing 100083, P.R. China. Contact email: [email protected], [email protected] JIANTAO JU is with the School of Metallurgical Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, P.R. China. Manuscript submitted July 23, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
In the production of Ti-containing steel and alloy by ESR, the TiO2 content in the slag gradually increases during ESR process because of the introduction of the oxidation products of titanium from liquid metal into the slag pool. ESR industrial production practices showed that the TiO2 content in the slag increased by about 20 pct in many cases.[7–9] The continuous increasing of TiO2 content in the slag pool causes the change in the thermophysical properties of slag, such as crystallization behavior of the slag, which lead to ever-changing horizontal heat transfer in molds through slag films.[10,11] This frequently causes unstable operation and poor surface quality of the as-cast ingot during ESR production.[12] To stabilize the surface quality of as-cast ingot, it is necessary to carry out the research on the crystallization behavior of ESR-type slag with varying TiO2 contents. Many efforts have been carried out to study the crystallization behavior of TiO2-bearing metallurgical slag. Shi et al.[13] studied the effect of TiO2 addition on the isothermal crystallization behavior of the conventional high fluoride CaF2-CaO-Al2O3 slag system and found that the addition of 8.1 mass pct TiO2 largely enhanced the slag crystallization and suppressed the
fluoride evaporation from the slag melt. Li et al.[14] found that the overall crystallization of mold fluxes was promoted with the addition of TiO2 content. Silva et al.[15] showed that TiO2 is likely to reduce the effect of MgO on the crystallization of CaO-SiO2-Al2O3-based mold fluxes because of the strong glass former characteristic of TiO2. Hao et al.[16] demonstrated that increasing the TiO2 content from 0 to 12 mass pct resulted in a decrease of the melting temperature and solidification temperature of mold fluxes in titanium-stabilized stainless steel. Bothma and Pistorius[17] reported that lower TiO2 content (< 6 pct) decreased the overall liquidus temperature of mold fluxes, which increased rapidly aga
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