Crystallization Kinetics and Structure of Mold Fluxes with SiO 2 Being Substituted by TiO 2 for Casting of Titanium-Stab
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MOLD flux, as one of the most important issues contributing to the formation of sound continuous casting product of titanium-stabilized stainless steel, plays an irreplaceable role during the continuous casting process.[1,2] Throughout the casting of titanium-stabilized stainless steel, concentration of TiO2 in molten mold fluxes is increasing gradually due to the following primary reasons: (1) Mold powder can inevitably pick up the inclusions containing TiO2 or TiN floating up from liquid steel and, (2) the titanium in steel can be oxidized by SiO2 in mold powder to form TiO2, which enters into mold flux to cause an increase of TiO2 concentration in molten mold slag and the probable reaction is as follows[2–7]: ½Ti þ ðSiO2 Þ ¼ ðTiO2 Þ þ ½Si
½1
The increase of TiO2 concentration in molten mold slag could lead to some changes of physicochemical properties of mold flux, such as viscosity, solidification temperature, and crystallization behavior, which have strong influences on performance of mold fluxes, such as heat transfer and lubricity, to achieve a uniform shell and prevent sticking against the mold surface in the process of continuous casting.[4–13] Some investigations have been carried out to study the effects of different TiO2 content on the viscosity, solidifiZHEN WANG, Doctoral Candidate, QIFENG SHU, Associate Professor, and KUOCHIH CHOU, Professor, are with the State Key Laboratory of Advanced Metallurgy and Department of Physical Chemistry of Metallurgy, School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Yejin building room 714, Xueyuan Road 30#, Beijing 100083, P.R. China. Contact e-mail: [email protected] Manuscript submitted May 7, 2012. Article published online February 16, 2013. 606—VOLUME 44B, JUNE 2013
cation temperature, and crystallization behavior of mold flux, indicating that the viscosity of mold flux may decrease with an increase of TiO2 content at a high temperature, and the existence of TiO2 in mold fluxes can lead to the precipitation of crystals (CaTiO3 or CaSiTiO5), which could bring effects on heat transfer performance of mold fluxes.[4–7,12,13] However, these previous studies are very limited in clearly demonstrating the crystallization kinetics processes of mold flux with titanium in steel being oxidized by SiO2 or with the absorption of TiO2 in the continuous casting process of titanium-stabilized stainless steel. In addition, the physiochemical properties of slag are closely related to the structure, and changes of physiochemical properties can be determined or explained by the investigation of structure characteristics. Structural studies on mold fluxes are very limited with only a few cases.[14,15] To the best knowledge of the authors, no investigation on the structure of TiO2-bearing mold fluxes in the casting of Tistabilized stainless steel was reported. Consequently, it is essential to carry out the research on the structure of mold fluxes in casting of Ti-stabilized stainless steel and behavior of crystallization. Solid film of mold flu
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