单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,Study on the Macrosegregation Behavior of the Bloom Continuous Castings,大方坯,/,圆坯连铸宏观偏析特性与注流控制技术应用,孙海波，张家泉,报告人：张家泉,北京科技大学钢铁冶金系,Phone,：,139 111 71237,Outline/,提纲,Introduction/,引言,Coupled model development/,连铸凝固过程电磁热溶质耦合模型开发,(electromagnetic-thermal-solute transportation),Macroscale,transport phenomena in bloom CC process/,大方坯连铸过程传输现象特征,Low temperature casting technology/,铸坯宏观偏析控制技术与应用效果,Conclusions/,结论,Introduction,Macrosegregation has been the bottleneck for the internal quality upgrading of the casting products.,For the efficiency limitation of industrial tests,previous researcher have devoted significant efforts to develop the mathematical models for better understanding the macro-segregation,At present,representative models mainly include:,Continuum model,(by F.P.,Incropera,Int.J.Heat Mass Transfer,1991 and H.L.Tsai,Metall,.Trans.A,1993),Volumetric averaging model,(by,C.Beckermann,Metall,.Trans.B,1991 and D.R.Poirier,Metall,.Trans.B,1991),For the CC process,few investigations were reported to reveal the macrosegregation.Reasons can be summarized as:,More complicated physical,phenomena,(,such as,the moving solidification front,varying heat boundary condition,turbulent flow and EMS,),Enormous calculated,quantity,(,computational domain involves the region between meniscus and final solidification destination,),In the present work,a mathematical model,coupling electro-magnetism,fluid flow,heat and solute transport,was developed based on the 3D plus 2D hybrid modeling method for the bloom CC process.,Coupled model development,Implementation process for the multi physics/scale mathematical model,Fluid flow model,1)Continuity equation,2)Momentum equation,a)Thermo-,solutal,buoyancy,(1),(2),(3),b),Electromagnetism force,calculated by the finite element code ANSYS,is imported into the Fluent code as the momentum source term through the coordinate interpolation algorithm.,Schematic of coordinate,interpolation algorithm,c)Phase interaction force within the mushy zone,can be described by the Darcys law:,where,the permeability,K,p,was calculated by using the Carman-Kozeny equation:,3)Low-Reynolds number turbulent model,2.Solidification and heat transfer model,Enthalpy equation,where,Enthalpy:Liquid,Fraction:,moreover,Solute element,C,78.0,Si,7.6,Mn,4.9,P,34.4,S,38.0,Slope of liquidus line,1,1 Y.Ueshima,S.Mizoguchi,T.Matsumiya et al.Analysis of Solute Distribution in Dendrites of Carbon Steel with/Tansformation during SolidificationJ.Metallurgical Transactions B.1986.17B(12):845-859.,3.Solute transport model,Solute transport equation,where,Moreover,the source term,S,s,consists of the molecular diffusion,S,s,dif,induced by Fickians law and the convection diffusion S,s,con,:,In consideration of,1),the ratio of longitudinal heat flux to the total heat is only about 36%,2),the temperature of molten steel at the strand center gradually decreases along the casting direction,in the CC process:,Z-component of velocity variation for the center molten steel of strand along the casting direction,Division of computational domain for the CC system,4.Division of computational domain,5.Meshes,Meshes adopted in the heat and solute transport model for turbulent flow region(a),natural convection region(b)and forced convection region(c).,Meshes adopted in the electromagnetic model for M-EMS(a),and F-EMS(b).,6.Boundary condition,1.Inlet and outlet,At the cross section of inlet,v,z,=v,in,v,x,=v,y,=0,K,in,=0.01v,in,2,=K,in,1.5,/D,T,in,=T,c,and C,in,=C,steel,.For the outlet,the fully developed flow condition was adopted.,2.Free surface,Adiabatic condition,normal gradients of all variables at free surface was set be zero.,3.Strand surface,a)Mould zone,b)Secondary cooling zone,c)Air cooling zone,4.Electric current density,Macroscale transport,phenomena in bloom CC process,Operation condition,Parameters,Value,Parameters,Value,Sectional dimension,260300 mm,2,Current of M-EMS,200A,Casting speed,0.65m/min,Frequency of M-EMS,3.0Hz,Superheat degree,29,Current of F-EMS,100A,Steel grade,GCr15,Frequency of F-EMS,12.0Hz,Steel grade,Chemical composition(wt%),C,Si,Mn,P,S,GCr15,0.951.05,0.150.35,0.250.45,0.020,0.020,Table 1,Operation condition of casting test,Table 2,Chemical composition of the steel grade,Sectional shape,Casting speed,m/min,Cooling water flow rate,，,L/min,Zone 0,Zone 1,Zone 2,Zone 3,Zone 4,Zone 5,Bloom casting,0.65,26.3,20,14.7,18.9,15.8,9.5,Cooling zone length,，,m,0.56,1.19,1.49,2.3,2.3,1.19,Table 3,Length and cooling water flow rate of each cooling loop in the secondary cooling zone,Electromagnetic field,Comparison between calculated and measured value of magnetic induction intensities in the stirrer center under the cases of different current and frequency,Calculated value variation of center MII along the casting direction,Variation tendency matches well with the results measured by L.B.Trindade,2,2 L.B.Trindade,A.C.F.Vilela,A.F.F.Filho et al.Numerical model of Electromagnetic Stirring for Co