Effect of Agitation on Crystallization Behavior of CaO-Al 2 O 3 -SiO 2 -Na 2 O-CaF 2 Mold Fluxes with Varying Basicity
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NTRODUCTION
MOLD fluxes play an indispensable role in the continuous casting process of steel. It is due to the fact that mold flux could provide the following functions[1–4]: (1) protecting the meniscus of the steel from oxidation; (2) providing thermal insulation; (3) providing liquid fluxes to lubricate the strand; (4) provide the optimal level of heat transfer; and (5) absorbing inclusions from the steel. These functions are closely related to the quality of casting products. It is well known that the viscosity and crystallization behaviors of mold fluxes are two of the most important parameters to ensure implementations of above-mentioned functions.[2,5,6] Suitable viscosity and crystallization behavior of mold fluxes can ensure the full lubrication and effective heat transfer control in the casting of steel. During the casting process, the oscillation of copper mold will generate shear stress on mold fluxes, which could cause variation on the property of mold fluxes, e.g., crystallization behavior.[7,8] As a result, there could emerge casting problems if effects of the external force field on mold fluxes are not well understood. In order to accurately evaluate the performance of mold fluxes, it is essential to study the effects of shear stress field on the mold flux. There are only a few studies dealing with effects of shear stress fields on the crystallization of slags.[9–11] Saito et al.[10] firstly exerted a shear stress field to slag by agitating the liquid slag using a Pt-Rh rod, and investigated the effects of agitation on crystallization JIANGLING LI, Doctoral Student, QIFENG SHU, Associate Professor, and KUOCHIH CHOU, Professor, are with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology, Beijing 100083, P.R. China, and also with School of Metallurgical and Ecological Engineering, University of Science and Technology, Beijing 100083, P.R. China. Contact e-mail: shuqifeng@ gmail.com Manuscript submitted January 11, 2015. Article published online April 28, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
behavior of CaO-SiO2-R2O (R = Li, Na, or K). The crystallization temperature was determined using a novel technique which is based on the difference in electrical permittivity of the ionic liquid and solid. They found that crystallization temperatures of investigated slags were increased by agitation. Harada et al.[11] employed the similar method to investigate the effect of agitation on crystallization behavior of CaO-SiO2-CaF2 melts. The results showed that crystallization of dendritic CaOÆSiO2 was strongly affected by the agitation and the crystallization of faceted cuspidine (Ca4Si2O7F2) showed little dependence on the agitation. However, it can be seen that previous studies are mainly about the simple slag systems, and there is no reference about the multicomponent slag systems. In the present work, the effects of agitation on crystallization of the multicomponent mold flux systems with varying basicity (defined as R = w(CaO)/w(SiO2), w(CaO), and w(SiO2) are mass percentages of CaO and SiO
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