Effects Of Crystallization Behavior Of Mould Fluxes On Properties Of Liquid Slag Film

Mould flux is an essential material used in continuous casting process, and whichhas a significant impact on the surface and subsurface quality of casting slabs. With thedevelopment of continuous casting technology, the quality requirement of mould fluxes,especially the mould fluxes for peritectic steel continuous casting, has been requiredhigher and higher. How to coordinate the contradiction between lubrication and heattransfer control now has become an essential problem, but also a big challenge for us.As lubrication and heat transfer control of mould fluxes are achieved and affected bycrystallization of slag film, and factors which affect this crystallization is numerous. It isvery hard to simulate the crystallization process of slag film in labs, and as a result ofthis, we have not enough understanding about characteristics of slag film. This will bean obstacle for the theory development of mould fluxes.This paper based on the contradiction between lubrication and heat transfer controlof slag film in peritectic steel continuous casting. Mould fluxes with different basicityand fluorine content were selected. After crystallization, the property change ofpost-precipitated liquid slag and its impact on continuous casting were obtained viacalculation and experiment, the affection of this change also has been discussed. Thencrystallization and lubrication characters of high basicity mould fluxes were discussedbased on exploratory experiment.Traditional CaO-SiO₂-CaF₂based mould fluxes and CaO-SiO₂-Na₂O,CaO-SiO₂-TiO₂based F-free mould fluxes were selected and the property change ofliquid slag film after single crystallization phase has been separated based calculationand experiment were obtained and discussed. The results reveal that even the originalproperties are similar. Property change rules of remaining mould fluxes could be verydifferent with different crystallization phase in different mould fluxes. Viscosity ofCaO-SiO₂-TiO₂based remaining liquid slags increase obviously after crystallization,and its crystallization capacity decrease rapidly. Melting temperature and crystallizationcapacity of CaO-SiO₂-Na₂O based remaining liquid slag increase rapidly. Propertychanges of CaO-SiO₂-CaF₂based remaining liquid slag are relative stable, and whichmeans CaO-SiO₂-CaF₂based mould fluxes is better than CaO-SiO₂-Na₂O andCaO-SiO₂-TiO₂based ones.Based on the results before, traditional CaO-SiO₂-CaF₂based mould fluxes for peritectic steel continuous casting were selected, and a steel bar for separating crystalsand liquid slag directly was adopted in this section. Properties of traditionalCaO-SiO₂-CaF₂based remaining slag were tested after took away crystals directly use apre-heated steel bar. The results reveal that crystallization capacity of remaining slags ofCaO-SiO₂-CaF₂based samples will increase in some degrees after crystallization. Thosemould fluxes are no more suitable for high speed peritectic steel slab continuous casting.The increase of crystallization capacity of remaining liquid slag maybe is the mainreason for the instability of traditional high crystallization capacity mould fluxes.Crystallization and lubrication property of high basicity mould fluxes werediscussed based on exploratory experiment. Properties of mould fluxes under differentbasicity were tested, and the possibility of high bascity mould fluxes was discussedbased on the requirements of high speed peritectic steel continuous casting. At last, anew method to coordinate the contradiction between lubrication and heat transfercontrol was presented, which has been proved excellent on coordinate the contradictionbetween lubrication and heat transfer control.