Thermodynamics And Kinetics On Precipitation Of Titanium Compound In Hot Metal

With the rapid development of iron and steel industries in China recently,production of iron and steel has increased for years,many blast furnaces are under high smelting intensity operation chronically,which leads to the increament of the ersion of blast furnace hearth and wall.Frequent accidents of burn-off at hearth account to huge losses.To prolong the life of hearth effectively,ironmaking workers do a lot of research work.Theory study and practice both show that adding a certain amount of titanomagnetite durning the blast furnace smelting process can effectively prevent slag iron further erosion to refractory materials,this is because Ti(C,N),a high melting point materia,forms in furnace bottom eroded area.But the feedback from different production practice has great difference,For(TiO2)-Fe-[C]-[N]-[Ti]-[Si,Mn,P,S,V]multiple systems in hot metal.Researches on precipitation condition of TiC and TiN has not yet been reported.Therefore,exploration the mechanism further on lining protection by titanomagnetite is of great significance.This thesis is based on schreyerite maintenance process,discussing thermodynamics and kinetics of the precipitation of TiC and TiN in blast furnace slag containing titanium dioxide and carbon saturated iron.Combined with high temperature confocal microscope and scanning electron microscopy of high temperature,molten iron,pig iron and furnace bottom sediments are tested and analysed.Main thermodynamic conclusions as follow:(1)Thermodynamic calculation shows that when W(TiO2)is constant,w[Ti]balanced with TiO2 in slag increases quickly with the rise of temperature.and when temperature is constant,W[Ti]balanced with TiO2 in slag increases with the rise of w(TiO2).Under the condition of blast furnace hearth,when w(TiO2)is 2%?5%and 10%,w[Ti]balanced with TiO2 in slag is 0.29%?0.71%and 1.37%respectively.(2)Draw the equilibrium advantage regional graph of reduction of TiO2,precipitation of TiC and TiN in molten iron by calculation.Under the condition of blast furnace hearth,[Ti]reduced in hot metal is mainly generates TiN.(3)Using titanomagnetite to protect the blast furnace hearth or smelting titanomagnetite,the content of titanium in molten iron is between 0.15%?0.18%,which is mainly because the fluctuation of temperature and nitrogen partial pressure in blast furnace is low.The critical amount of titanium to generate TiN almost unchanged.When the titanium content in molten iron is higher than the equilibrium value,TiN will precipitate from molten iron,which maintains content of titanium in hot metal at a certain level.Try to use nucleation-diffusion growth-collision theory to analyse TiN particles precipitate,main conclusions include:(4)Kinetic condition of TiN nucleation in molten iron is studied by classical nucleation theory,and results show that when the temperature is low,molten homogeneous nucleation rates of TiN in hot metal is nearly 0,when the temperature of hot metal reaches 1540?,the homogeneous nucleation of TiN can go with a swing.Nucleation of TiN in molten iron is mainly based on heterogeneous nucleation,under the condition of blast furnace temperature,the ratio of dissolved content of titanium and criticalti content to generate TiN reaches 3,heterogeneous nucleation can be fully conducted.(5)According to the diffusion theory,growth rate of TiN particles is calculated durning the diffusion-reaction-precipitation process,and concludes that diffusion is the restrictive step durning the process.TiN grows up to 1.5?m in 1s.Brown collision happens in submicron size,particles only grow up to 0.6?m in 20 min;Turbulent collision and Stokes collision are the main way for growth of TiNparticles,particles can grow up to 18?m and 11? in 1min.(6)The cores of primary TiN are mainly TiO2 and graphite durning the process of heterogeneous nucleation,while the core of primary TiC is mainly Al2O3.Lattice mismatch between TiO2,graphite and TiN is 4%and 5.32%respectively,Lattice mismatch of Al2O3 and TiC is 8.7%.Lattice mismatch is small,so heterogeneous nucleation of TiC,TiN can be conducted on the surface.Lattice mismatch between TiN and CaO,MnO,SiO2,MgO in molten iron is 13%,35.6%,14.6%,13%respectively,larger,so the TiN on the surface of heterogeneous nucleation is difficult to conduct because the lattice mismatch is larger.(7)Titanium Compound in bottom sediments is mainly polymerized TiN and TiC particles,the size of a single TiN or TiC particle is 5-30?m,which is consistent with results of the model of collision growth previously.