Development of Non-reactive F-Free Mold Fluxes for High Aluminum Steels: Non-isothermal Crystallization Kinetics for Dev
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he development of non-reactive F-free mold fluxes for the continuous casting of high aluminum steels, it is imperative to understand their crystallization behavior in the mold, since control of horizontal heat transfer is related to crystallization tendency. An inappropriate control of heat transfer in
QIFENG SHU is with the Research Unit of Process Metallurgy, University of Oulu, 90014 Oulu, Finland and also with the School of Metallurgical and Ecological Engineering, University of Science and Technology, Beijing, Beijing 100083, China. Contact emails: [email protected], qifeng.shu@oulu.fi QIANGQI LI is with the School of Metallurgical and Ecological Engineering, University of Science and Technology. SAMUEL LUCAS SANTOS MEDEIROS and JEFERSON LEANDRO KLUG are with the Postgraduate Program in Materials Science and Engineering, Federal University of Ceara´, Fortaleza, Ceara´, CEP 60440-554, Brazil. Manuscript submitted July 17, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
continuous casting process can result in breakout if heat transfer rate is too low, or longitudinal cracks if heat transfer rate is too high. Mold fluxes play a crucial role in the continuous casting of defect-free steel products, providing appropriate heat transfer control, lubrication, thermal insulation, inclusion absorption, and oxidation prevention.[1] It is well accepted that horizontal heat transfer rate can be controlled when controlling mold slag crystallization.[2,3] Transformation-induced plasticity (TRIP) steel has become a new representative of advanced high-strength steel for lightweight automotive applications. During continuous casting of high aluminum steels using traditional CaO-SiO2-CaF2 based mold fluxes, operational issues and quality problems arise due to the steel/ slag interfacial reaction: Al + (SiO2) = Si + (Al2O3). This reaction is fast and leads to increase of Al2O3 content in the mold slag, causing problems such as massive formation of slag rim, poor lubrication, and uneven horizontal heat transfer. To deal with this
question, a possibility is to remove SiO2 from mold flux, which would result in ‘‘non-reactive’’ mold fluxes, i.e., the reaction could not happen.[4–6] Another industry demand related to mold fluxes is the need for eliminating fluorine from their composition. Volatile and water-soluble fluorine compounds are formed when using traditional CaO-SiO2-CaF2-based mold fluxes, causing corrosion of casting facilities and environmental pollution.[7–10] Any potential substitute—B2O3, Na2O, Li2O, TiO2—or a combination of them should play the same role as fluorine regarding the technological parameters viscosity, crystallization behavior, and characteristic temperatures got from heating microscope.[5] In order to deal with these demands, in a previous study, several recipes of F-free CaO-Al2O3-based mold fluxes were proposed and evaluated. In this study,[5] it was reported that, for some compositions in the CaO-Al2O3-B2O3-Na2O-Li2O system, the viscosity and melting temperature were close to traditional CaOSiO2-CaF2 mold flu
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