Development of non-reactive F-free mold fluxes for high aluminum steels : non-isothermal crystallization kinetics for devitrification
Shu, Qifeng; Li, Qiangq; Santos Medeiros, Samuel Lucas; Leandro Klug, Jeferson (2020-04-14)
Shu, Q., Li, Q., Medeiros, S.L.S. et al. Development of Non-reactive F-Free Mold Fluxes for High Aluminum Steels: Non-isothermal Crystallization Kinetics for Devitrification. Metall and Materi Trans B 51, 1169–1180 (2020). https://doi.org/10.1007/s11663-020-01838-4
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https://urn.fi/URN:NBN:fi-fe2020060942405
Tiivistelmä
Abstract
It is necessary to study crystallization from glass (devitrification) for non-reactive F-free CaO-Al₂O₃ based mold fluxes; this is especially important for the development of mold fluxes for continuous casting of high aluminum steels. To the knowledge of the authors, there is no report in the literature regarding devitrification of F-free mold fluxes based on the CaO-Al₂O₃-B₂O₃-Na₂O-Li₂O system. Therefore, crystallization kinetics for particular compositions in this system, with different w(CaO)/w(Al₂O₃) ratios, was investigated by Differential Scanning Calorimeter, Field-Emission Environmental Scanning Electron Microscopy / Energy Dispersive Spectroscopy, and X-ray Diffraction techniques. The first crystal, which precipitates during heating from glass, is Ca₁₂Al₁₄O₃₃, followed by CaO. For the first crystal, which precipitates as plate-like (2-dimensional), it was found that, when using the Matusita–Sakka model, agreement between the calculated Avrami parameters and the micrographs obtained from electron microscope was reached. In the same way, agreement was found for the second event—CaO precipitation—which grows 2-dimensionally or 3-dimensionally, depending on the w(CaO)/w(Al₂O₃) ratio. The most important event (in terms of energy liberated and amount of crystals) is Ca₁₂Al₁₄O₃₃ precipitation. For this event, the effective activation energy for crystallization, EG, decreases with the increase of w(CaO)/w(Al₂O₃) ratio. The activation energy for crystallization reflects the energy barrier for crystallization. Thus, it can be concluded that mold fluxes crystallization during heating is enhanced when increasing the w(CaO)/w(Al₂O₃) ratio, for constant contents of B₂O₃, Na₂O, and Li₂O.
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