Study On Preparing Of Low Oxygen Content High Ferrotitanium By Aluminothermic Reduction-Vacuum Refining

High titanium content ferroalloy is a kind of special midtermalloy with wide application. It is a kind of indispensable material for smelting iron-basic superalloys and high quality stainless steels. Especially it plays a key role in improving the qualities of high grade alloy-steels in using military and aviation. With the increasing demand of different kind and quality of steels, the quality of titanium ferroalloy need to be controlled more strictly. At present producing of high titanium ferroalloy mainly adopts aluminothermic deoxidization method, which has many advantages such as the source of materials is extensive, the price is cheap and product cost is low. But the oxygen content in the high titanium ferroalloy prepared by this method is too higher to satisfy customer's reqirements. So its application is limited. In current all high-quality high titanium ferroalloy needed in our country is dependent on importing from outside, and the cost is very expensive. This seriously restricts the development of our country's high and new technology.In this thesis, by observing the microstructures of high ferrotitanium and analyzing forming mechanism of oxygen in now available process of preparing high ferrotitanium, a kind of new process is put forward to prepare high ferrotitanium with high-quality and low oxygen content by the method of aluminothermic reduction- vacuum refining. That is, preparing of the rough product of high ferrotitanium by aluminothermic reduction method firstly, then refining it under vacuum condition. High quality ferrotitanium is prepared by adding composite deoxidition agent and forming complex slag, removing lard from high ferrotitanium.The analysis of microstructure indicates that the deoxiding reaction preparing of high ferrotitanium by aluminothermic reduction process is not complete at present. Oxygen exists in complicated form of Al₂O₃, Fe₂TiO4, TiO₂, Ti₂O, and Titanic-Oxygen solid solution. The microstructure of ferrotitanium is complicate, the chemical property of forming oxide lard is stable and the slag is separated from the alloy hardly. The thermal insulation time in smelting is extended and the condition of separating the slag from the alloy is improved, but oxygen consistency in titanium ferroalloy increase because that the diffusion action of oxygen from the air results to get the high titanium ferroalloy of low oxygen content hardly.According to the analysis to the components of the lard in high ferrotitanium and the forming mechanism of oxygen, in this thesis, selecting Al-Mg as reducing material, CaO-Al₂O₃-CaF₂ as basic slag system, CaO-Al₂O₃-CaF₂-TiO₂ and CaO-Al₂O₃-CaF₂-SiO₂ as four unit slag system, the effect of the content of TiO₂ and SiO₂ on the viscosity and fluidity are inspected, the viscosity of slag is measured, the changes of the phase is analyzed.Viscosity tests shows that the slag viscosity decreases with growing temperature and increasing the content of CaF₂. At the temperature is above 15₂0℃, Viscosity is below 0.4 Pa·S, the fluidity of CaO-Al₂O₃-CaF₂-TiO₂ slag system is better. The major phases of smelted slag are ₃CaO·Al₂O₃, 1₂ CaO·7Al₂O₃, Ca1₂Al14O₃₂F₂, Ca₃(AlO₃)₂ and CaTiO₃. At the temperature is above 149₂℃, Viscosity is below 0.4 Pa·S, the fluidity of CaO-Al₂O₃-CaF₂-SiO₂ slag system is better. The more additives of SiO₂ the lower viscosity is. The major phases of smelted slag are Cal₂Al14O₃₂F₂, Ca₂SiO4, Ca₂SiO₂F₂, Ca₃Al₂(SiO4)₃, 5CaO·₃Al₂O₃ and Al₂(SiO₄)O.The results of vacuum refining show that the Al-(10%^<sub>20%)Mg is an effective compound reducing material, CaO-(10%²0%)CaF₂-(10%¹5%)Li₂O is a fine slag system, which is very effective for eliminating oxide impurities in high ferrotitanium and decreasing oxygen content in alloy. After vacuum refining the contents of aluminium and silicon in alloy come up standards , the contents of oxygen is decreased effectively comparing to rough ferrotitanium from 12.20% to 3.25%.