Effects of crystallisation behaviour of mould fluxes on properties of liquid slag film

Abstract

During the continuous casting of medium carbon steel slabs, stable liquid slag film performance is necessary to ensure that the process runs smoothly. In this paper, the effects of mould flux crystallisation behaviour on the properties of leftover liquid slag films were examined. First, the compositions of the leftover liquid slags of high fluorine, CaO-SiO 2 -TiO 2 and CaO-SiO 2 -Na 2 O based mould fluxes after a single crystalline phase was separated were calculated. Then, the viscosity, melting temperature, break temperature and degree of crystallisation of each leftover liquid flux were measured. The results revealed that the properties of leftover liquid slag films of CaO-SiO 2 -TiO 2 and CaO-SiO 2 -Na 2 O based mould fluxes are not as stable as those of high fluorine films after crystallisation. This paper provides a new method for developing fluorine free mould fluxes and for determining the most suitable type of crystalline phase that should be utilised in the continuous casting of medium carbon steel slabs.

Molecular dynamics simulations of microstructural properties of CaO–SiO2–TiO2 fluorine-free slag systems

“…1 In order to determine an appropriate substitute for the cuspidine (3CaO-2SiO 2 -CaF 2 ) mineral for heat transfer control, some different crystalline phases were studied, such as gehlenite (CaO-Al 2 O 3 -SiO 2 ), perovskite (CaO-TiO 2 ), CaO-SiO 2 -Na 2 O (CSN) and CaO-SiO 2 -TiO 2 (CST). [2][3][4] The properties of slags, such as the viscosity and crystallisation behaviour, have been investigated by many metallurgists. The structures of calcium silicate-based slags have been investigated by steelmakers using Fourier transform infrared spectroscopy (FTIR), Raman spectra, nuclear magnetic resonance and other methods.…”

Review on the High-Temperature Thermophysical Properties of Continuous Casting Mold Fluxes for Highly Alloyed Steels

“…For casting high-Ti steels with CaO-SiO 2 -based mold fluxes, F has been replaced with TiO 2 to generate the perovskite primary crystal phase, thereby substituting the cuspidine phase to control the heat transfer. 27,125,126) It has been speculated that TiO 2 reduces the infrared transmittance of the slag film and inhibits radiation heat transfer. In addition, Nakada and Nagata 127) also observed that the incubation time for titanite (CaSiTiO 5 ) nucleation in CaO-SiO 2 -TiO 2 slags was comparable to that of the cuspidine phase in commercial mold fluxes, which suggests that the CaSiTiO 5 could also crystallize rapidly in slag films similar to cuspidine in commercial mold fluxes.…”

Structure of Solidified Films of CaO-SiO2-Na2O Based Low-Fluorine Mold Flux

“…Experimental samples were prepared using analytical-grade reagents (CaCO 3 , SiO 2 , Na 2 CO 3 , CaF 2 , and Al 2 O 3 ). The physical properties were measured (see Table 2) [20][21][22]. The melting temperature was measured by the hemisphere point method; the high temperature viscosity and viscosity-temperature curve were measured by a high-temperature rotational viscometer (using graphite bobs with 15 mm diameter and graphite crucibles with 55 mm inner diameter).…”