| High titanium steel has good properties such as high strength,corrosion resistance and reducing welding spatter,which makes it widely developed and applied at home and abroad.However,the interfacial reaction between steel and mold flux is serious in the casting process of high titanium steel,which leads to the surface quality problem of the billet and makes the continuous casting with multiple furnaces difficult.In this paper,a new type non-reactive CaO-Al2O3-TiO2-based non-fluorine mold flux for high titanium steel is developed.Meanwhile,the perovskite is used to replace cuspidine to control heat transfer and realize the non-fluorine mold flux.Firstly,the relationship between the critical content of components in mold flux is analyzed by the thermodynamic calculation,it is clear that there is no interfacial reaction of between steel and mold flux when w(TiO2%)?2%and w(SiO2%)?5%.The kinetics model of interfacial reaction between steel and mold flux is established based on double-film theory,and the restrictive step of interfacial reaction is Ti,Si,TiO2 and SiO2,among which the influence of Ti is the most significant.The interface reaction degree and reaction equilibrium time are increased when Ti content is in the range of 0.05%to 1.91%,and the predicted values are consistent with the testing values.Above all,the composition range of mold flux is preliminarily acquired.Secondly,the effects of components on melting property,rheological property,crystalline property and heat transfer property of mold flux are systematically analyzed by automatic tester slag melting point and melting speed,rotary viscometer,S/DHTT and infrared emitter system.The viscosity is controlled at 0.1?0.5 Pa·s by combining the characteristics of BaO reducing the degree of polymerization of Al-O and Ti-O structural units in the melt,furthermore,BaO solve the difficulty of high melting point of CaO-Al2O3-TiO2-based mold flux,and the melting point is controlled at 1050?1100?.The calculation model of melting temperature,viscosity and break temperature of a new type non-reactive CaO-Al2O3-TiO2-based non-fluorine mold flux for high titanium steel are developed,based on a large number of experimental dates.The metallurgical properties of mold flux can be accurately predicted by three models.The crystallization mechanism of mold flux is shown by Mo model during non-isothermal crystallization.It suggested that the interfacial reaction control is the controlling step of crystallization,most crystal nucleation is constant nucleation rate nucleation or constant nucleation number nucleation,and it is grown in two or three dimensions.When the TiO2 and Li2O contents are 16%and 8%,the crystals are nucleated at a constant rate and grew in three-dimensional growth mode.According to the analysis of the heat transfer characteristics of mold flux,the growth of above crystals can effectively control the heat transfer,and the non-fluorine mold flux with the effect of control the heat transfer is realized by the perovskite replaced the cuspidine.The phase state change and structure distribution are revealed by the DHTT double wire method,and it is shown that the three layers structure,glassy layer,crystalline layer and liquid slag layer,are more obvious.The thickness of glassy layer and crystalline layer are increased,and the thickness of liquid slag layer is decreased gradually when the temperature of shell is decreased in the mold.The development of mold flux is based on reliable experiment data and theoretical basis from the in-depth analysis of its metallurgical properties.Finally,according to the requirements of high titanium steel ER70-Ti for mold flux,the composition of new type non-reactive CaO-Al2O3-TiO2-based non-fluorine mold flux for ER70-Ti is acquired by the calculation of the model of melting temperature and viscosity.It is that CaO-Al2O3 is 0.8?1.2,the content of TiO2 is 4?12%,the content of SiO2 is 1?5%,the content of BaO is 5?15%,the content of Na2O is 6?10%,the content of Li2O is 1?4%,the content of B2O3 is 6?10%,the content of MgO is 2?4%.Then,CaO-Al2O3-TiO2-based mold flux is produced and applied in the industrial production of ER70-Ti,and the application of it is successful. |
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