Thermochimica Acta 512 (2011) 129–133 Contents lists available at ScienceDirect Thermochimica Acta journal homepage: www.elsevier.com/locate/tca Thermodynamic modeling of mineralogical phases formed by continuous casting powders Julio Romo-Casta ˜ neda, Alejandro Cruz-Ramírez * , Antonio Romero-Serrano, Marissa Vargas-Ramírez, Manuel Hallen-López Metallurgy and Materials Department, Instituto Politecnico Nacional-ESIQIE, Apdo. P. 118-431, 07051 Mexico D.F., Mexico article info Article history: Received 2 July 2010 Received in revised form 10 September 2010 Accepted 15 September 2010 Available online 21 September 2010 Keywords: Thermodynamic Flux Solidification Mineralogical phases Cuspidine abstract A great amount of mineralogical phases were predicted and represented in stability phase diagrams, which were obtained by the use of the thermodynamic software FACTSage considering both the chemical composition and the melting temperature of the mould flux. Melting-solidification tests on commercial mould flux glasses for thin slab casting of steel revealed the existence of cuspidine (Ca 4 Si 2 O 7 F 2 ) as the main mineralogical phase formed during the flux solidification by X-ray powder diffraction (XRD). This phase directly influences the heat transfer phenomena from the strand to the mould and it is obtained with higher fluorite content (22% CaF 2 ). Cuspidine is desirable only in fluxes to produce medium carbon (included peritectic grade) steels, because it reduces the heat flux from the strand to the mould, thus controlling the shrinkage rate during the flux solidification. The experimental results are in agreement with those obtained by the thermodynamic software. The stability phase diagrams could be used as an important tool in the flux design for continuous casting process. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Mould powders must fulfill several functions during the contin- uous casting of steel. They play an important role in the surface quality of the steel product and in the overall efficiency of the continuous casting process control [1]. More recently, high speed continuous casting was developed in order to improve productivity and conserve energy in the continuous casting of steel slabs [2,3]. Improvement in mould lubrication is therefore crucial for efficient high-speed casting, and mould powder has been developed for this purpose. Thin slab casting powders are mixtures of oxides generally based on the SiO 2 –CaO–CaF 2 –Na 2 O system. Three to six percent graphite is usually added to control the melting characteristics and to improve the thermal insulation properties of the fluxes [4]. The chemical composition and the physical form of the flux can control the melting temperature, melting rate, viscosity and surface tension of the flux. It has been found that viscosity and the melting temper- ature of the mould flux are increased when silica and alumina are added to the original composition of mould fluxes [5–7]. The size of the silicate or aluminosilicate network in casting powders or slags become larger with increasing SiO 2 and Al 2 O 3 contents, hence their mobility decreases resulting in a higher viscosity. The addition of * Corresponding author. Tel.: +52 55 5729 6000x54202; fax: +52 55 57296000x55270. E-mail address: alcruzr@ipn.mx (A. Cruz-Ramírez). metal oxides, such as Na 2 O, leads to the breakdown of the silicate network, resulting in lower viscosity. There are considerable varia- tions in the constituents used by powder manufacturers, and when the casting powders are heated the constituents react to form dif- ferent mineralogical phases. The mineralogical constitution of the powder is of particular importance since it affects the melting rate of the powder, the lubrication characteristics and the heat transfer between the strand and the mould, thus impacting decisively the casting performance [5,6]. Mills [7] represented the chemical com- position of casting powders by a pseudoternary system. Grieveson et al. [5] identified the phases formed in a wide range of chemi- cal compositions by controlling the rate of melting of the casting powder and an attempt to represent the mineralogical phases in a phase diagram was also made. Hiromoto et al. [8] identified the phases formed in five synthetic fluxes at various temperatures between 773 K and the melting point after quenching and analyzing by X-ray diffraction. They observed that above 1073 K the original constituents were replaced by more complex mixtures of oxides or oxyfluorides and that the concentrations of those complex com- pounds increased with temperature. The most abundant phases in the fluxes at higher temperatures were cuspidine (Ca 4 Si 2 O 7 F 2 ), and a pectolite phase (Na 2 CaSi 3 O 8 ) with smaller amounts of pseudo- wollastonite (CaSiO 3 ). When alumina was added to the powder, anorthite (CaAl 2 Si 2 O 8 ), gehlenite (Ca 2 Al 2 SiO 7 ), and nepheline (NaAlSiO 4 ) were also formed [8,9]. The kind of mineralogical phases formed affects the melting temperature and consequently the melt- ing rate of the powder. The phases formed when a liquid flux 0040-6031/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.tca.2010.09.014