Study On New Producing Zones Of Non-fluorine And Low-fluorine Continuous Casting Mould Fluxes

Mould fluxes is a very important and critical material during continuous casting of steel, takes a key role to improve quality of strands. Mould fluxes usually contain 2¹5% fluorine, due to its special influence on the high temperature physicochemical properties of mould fluxes. However, Fluoride can cause a series of environmental problems, so it's very important to reduce fluorine content in mould fluxes. On the base of research of development of non–fluorine mould fluxes both home and abroad, the problem of mould fluxes without fluorine was analyzed, that is how to keep the viscosity-temperature property at high temperature while casting high carbon steel and how to control the crystallizing property while casting peritectic steel or hypo-peritectic steel. The present research can deal with part of the problems after reducing fluorine in mould fluxes, but can cause other more problems. So, it is necessary to systematically estimate all the properties of mould fluxes and to seek the component area close to the mould fluxes bearing high fluorine for the research of non-fluorine and low-fluorine mould fluxes.Viscosity, melting temperature, breaking temperature and crystallizing temperature have been used as property index to estimate mould fluxes used in billet, low alloy high-intensity slab and hypo-peritectic steel slab casting. The slag system of non-fluorine and low-fluorine slag was designed by the simplicity grid method, the physiochemical properties at high temperature were testing and analyzed, the conclusions were as follows:①The new producing zones of non-fluorine mould fluxes are found in the simplicity grid designed area. The zones of slag system fit for low carbon slab mould fluxes are: TiO₂=6%, Li₂O=2%, B₂O₃ content are less than 3%;TiO₂=6%, Li₂O=0%,MnO content are more than 3.3%,less than 5%,B₂O₃ content are more than 3%;TiO₂=4%, Li₂O=0%,B₂O₃ content are more than 2%,less than 5%. Fluorine free slag fit for hypo-peritectic slab hasn't been found in this area. Other more, large quantity of slag fit for high carbon billet mould fluxes were found in the designed area.②The new producing zones of low-fluorine mould fluxes are found in the simplicity grid designed area. The zones of slag system fit for low carbon slab mould fluxes are TiO₂=6%, Li₂O=0%, B₂O₃ content are more than 2%, less than 8%; TiO₂=4%, Li₂O=0%,in the whole area of contour chart; TiO₂=0%, Li₂O=2%, B₂O₃ content are more than 2%,less than 5%.The zones of slag system fit for low alloy high-intensity steel slab mould fluxes are TiO₂=6%, Li₂O=0%, B₂O₃ content are more than 2%, MnO content are more than 4%,less than 5.2%.③Crystalline phase of mould fluxes bearing high fluorine is cuspidine (3CaO·2SiO₂·CaF₂). Crystalline phase of non-fluorine are Na₂O·2CaO·3SiO₂ and 2CaO·SiO₂. Melting temperature of Na₂O·2CaO·3SiO₂ is 1250℃, while melting temperature of 2CaO·SiO₂ is 2130℃, and the crystallizing temperature of this crystalline phase may be high in the cooling process. DSC results show that, the crystallizing temperature of non-fluorine slag is not in the proper range. It's effective to seek a crystalline phase which has a crystallizing property close to cuspidine in the coming research.