A Kinetic Study of the Effect of Basicity on the Mold Fluxes Crystallization
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MOLD flux has been used widely in continuous casting for lubricating the strand, adsorbing inclusions, moderating mold heat transfer, and insulating the molten steel free surface. The mold flux crystallization was regarded as one of the most important properties of mold flux, as primarily it controls the heat transfer and lubrication in the continuous casting mold.[1,2] The crystallization behavior of mold flux has been studied intensively. Kashiwaya et al.[3] first developed the single hot thermocouple technology (SHTT) and double hot thermocouple technology (DHTT) for in situ observation and measurement of crystallization of mold flux. Orrling and Cramb[4] considered the effect of water vapor on mold slag crystallization by using DHTT. Orrling et al.[5] discovered that the crystal morphology of mold flux was dependent on the degree of undercooling. Some other researchers investigated the effect of chemical compositions like F–,[6] Na2O,[7] Li2O,[8]
LEJUN ZHOU, Ph.D. Student, WANLIN WANG, Professor, FANJUN MA, Postdoctor, and JIN LI and JUAN WEI, Graduate Students, are with the School of Metallurgical Science and Engineering, Central South University, Changsha 410083, P. R. China. Contact e-mail: [email protected] HIROYUKI MATSUURA, Lecturer, and FUMITAKA TSUKIHASHI, Professor, are with the Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba 277-8561, Japan. Manuscript submitted May 27, 2011. Article published online October 27, 2011. 354—VOLUME 43B, APRIL 2012
Al2O3,[9] rare earth oxide,[10] etc. on the crystallization behavior of mold flux. However, the basicity of mold flux has been regarded as the most significant effect on the mold flux crystallization. The study of Li et al.[11] showed that the addition of CaO caused a dramatic increase in the amount of crystalline phase formed. Ryu et al.[12] found that the increase of basicity tended to improve the crystallization temperature and reduce the incubation time by using a confocal scanning laser microscopy. Although these were some results regarding basicity and mold flux crystallization being studied, few strategies have been developed to study systematically the effect of basicity on mold flux crystallization, especially in the view of kinetics. Therefore, a kinetic study of the effect of basicity on mold flux crystallization was carried out in this article by using an industrial low carbon steel mold flux with the basicity (CaO/SiO2) of 0.8 as the matrix flux (Table I). A kinetic study was conducted in the following ways: (1) constructing the time-temperature-transformation (TTT) diagrams and continuous-cooling-transformation (CCT) diagrams of mold fluxes with different basicity by using SHTT; (2) analyzing the influence of basicity on those key parameters, such as incubation time, crystallization temperature and critical cooling rate; (3) investigating the variations of effective crystallization rate and crystallization mechanisms of mold fluxes; and (4) calculating the crystallization activation energy of diff
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