Viscosity and Solidification Temperature of SiO_2-CaO-Na_2O Melts for Fluorine Free Mould Flux

摘要

Fluorine-free mould flux has been required to reduce corrosion of continuous casters. In this paper, Na_2Ca_2Si_3O_9 has been applied to an alternative crystalline phase of Ca_4Si_2O_7F_2 (cuspidine) that crystallized in commercial flux films. Effects of basicity described as T.CaO/SiO_2 and additions of Li_2O, Na_2O, MgO and/or MnO into Na_2Ca_2Si_3O_9 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, Na_2Ca_2Si_3O_9, decreased while that of Na_2Ca_2Si_2O_7, which had higher melting point than the target phase, increased. It is indicated that the solidification temperature is related to Na_2Ca_2Si_2O_7 crystallization. Carbon steel was cast with one of the developed fluorin-free mould fluxes and slab without any surface cracking was obtained.