Viscosity and solidification temperature of SiO2-CaO-Na 2O melts for fluorine free mould flux

Abstract

Fluorine-free mould flux has been required to reduce corrosion of continuous casters. In this paper, Na2Ca2Si 3O9 has been applied to an alternative crystalline phase of Ca4Si2O7F2 (cuspidine) that crystallized in commercial flux films. Effects of basicity described as T.CaO/SiO2 and additions of Li2O, Na2O, MgO and/or MnO into Na2Ca2Si3O9 composition mould flux on viscosity and solidification temperature were studied and the solidified specimens were examined by X-ray diffraction to identified crystalline phases. The viscosity of the mould flux is reduced with increaing of the basicity or the basic components contents. The solidification temperature decreased slightly as the basicity increased from 0.47 to 0.60, whereas it increased steeply with increasing of the basicity from 0.60 to 0.70. The solidification temperature also steeply increased when large amounts of these basic components were added. With increasing of the basic components amounts, the first peak intensity of the target phase, Na2Ca 2Si3O9, decreased while that of Na 2Ca2Si2O7, which had higher melting point than the target phase, increased. It is indicated that the solidification temperature is related to Na2Ca2Si2O 7 crystallization. Carbon steel was cast with one of the developed fluorin-free mould fluxes and slab without any surface cracking was obtained. © 2013 ISIJ.