A Kinetic Study of the Effect of ZrO 2 and CaO/Al 2 O 3 Ratios on the Crystallization Behavior of a CaO-Al 2 O 3 -Based
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INTRODUCTION
IT is well known that mold flux is widely used in modern continuous casting process of steel, and its main functions include (1) protecting the liquid steel from oxidation, (2) lubricating the strand from sticking, (3) absorbing inclusions from the steel, and (4) modifying horizontal heat transfer for the molten steel to the water-cooled mold.[1–4] The crystallization behavior of mold flux is regarded as one of the most important properties of mold flux. Therefore, a series of techniques has been developed to study the crystallization behavior of the mold flux, which includes the differential thermal analysis (DTA),[5] hot stage microscopy such as confocal scanning laser microscopy (CLSM),[6,7] hot thermocouple technology (single and double thermocouple technology),[8,9] the water-cooled probe technique,[10,11] and infrared radiation emitter technique (IET).[12] Compared with the casting of conventional steels, the property and composition of mold flux vary greatly because of the intensive reactions between Al in the molten steel and silica in the flux when high-Al-grade steels were cast.[13–15] As a result, the mold slag crystallization changes dramatically, leading to the variation of in-mold liquid slag lubrication and heat transfer, which would in turn deteriorate the casting BINBIN JIANG, JUAN WEI, and BOXUN LU, Graduate Students, WANLIN WANG, Professor, IL SOHN, Associate Professor, and LEJUN ZHOU, Post Doctor, are with the School of Metallurgy and Environment, Central South University, Changsha 410083, P.R. China. Contact e-mail: [email protected] Manuscript submitted October 29, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
process as well as the surface quality of cast slabs. Therefore, the study of the crystallization behavior of mold flux for casting high-aluminum steels is important. Wang et al.[16] considered that Na2O restrained the crystallization of nonreactive high-alumina-containing mold fluxes. Wang et al,[17] investigated the solidification behavior of a new mold flux that was developed to be more compatible with high-aluminum-containing steels. Blazek et al.[18] stated that the solidification temperature and melting point decreased significantly with the addition of B2O3; however, the solidification temperature remained stable with variation of the C/A ratio, which ranged from 0.6 to 3.6 in lime-alumina-based mold flux. For lime-alumina-based mold flux, the C/A ratio has been identified as one of the most significant effects on the mold flux crystallization. Jung and Sohn[19] investigated that the crystallization temperature tended to decrease with the increase of C/A ratio by using a confocal scanning laser microscope for calciumaluminate system mold slag. Although some research of mold flux crystallization for casting high-Al steels has been conducted, very few studies have been developed to systematically investigate the effect of C/A ratio on limealumina-based mold flux crystallization behavior, which has the potential to be applied to the casting of high-Al steels The contamination of ZrO2 p
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