Numerical Simulation Of Solidification Structure And Electromagnetic Stirring Of High Carbon Steel Bloom In Continuous Casting

Macrosegregation is the main reason for affecting the internal quality of high carbon steel bloom in continuous casting.In order to effectively improve the internal quality of the bloom.The improvement of solidification structure of bloom and optimization of electromagnetic stirring process were investigated in this paper.In this paper,the high carbon steel bloom was taken as the research object.Firstly,the dendrite growth model was established by using the Cellular Automaton-Finite Difference Method(CA-FD)to study the evolution of dendritic growth morphology and the distribution of solute under different conditions.Furthermore,the dendrite growth model in solidification process was established by ProCAST to research the proportional distribution of equiaxed crystal regions under different boundary conditions.Secondly,referring to the operating condition in steel plant,a finite element model coupling electromagnetic field and fluid flow for Mold Electromagnetic Stirring(M-EMS)and Final Electromagnetic Stirring(F-EMS)were established by ANSYS and CFX software,respectively.The influences of process parameters on the electromagnetic field and flow field of bloom were analyzed systematically.Finally,based on the numerical simulation results,carried out industrial experiments and obtained optimal electromagnetic stirring process.The main conclusions were as follow:(1)For the growth of a single equiaxed dendrite,as the solidification time increased,the solute gradually enriched around the dendrite,resulting in microsegregation.As the undercooling increased from 20 K to 30 K,the carbon concentration of the dendritic tip increased from 0.986%to 1.267%,and microsegregation was more serious.The growth morphology of the equiaxed dendrite was quite different with the different preferred growth angle in the undercooled melt,and the degree of microsegregation was different.When the preferred angle was 0°,the secondary dendrites were less developed and the degree of microsegregation was lower.When the preferred angle was 30° and 60°,the secondary dendrites were the most developed,and the microsegregation was going to deteriorate further.(2)During the growth of columnar dendrites,as the solidification time increased,the solute continuously injected from the solid phase to the liquid phase around the secondary dendrite arm.As the secondary dendrites bridged each other,a closed region is formed,which marked it difficult for the solute elements to diffuse into the liquid phase,thereby causing the dendritic segregation to be intensified.At the same time,as the heat flux density applied at the bottom increased,the growth rate of the columnar dendrites increased,the dendrite became denser,and the microsegregation became more serious.(3)With the superheat increased from 25? to 45?,the ratio of equiaxed dendrite for high carbon steel in bloom continuous casting decreased from 35%to 31%.When the casting speed was increased from 0.65 m/min to 0.75 m/min,the ratio of equiaxed dendrite was increased from 32%to 34%.(4)In the numerical simulation of M-EMS,When the frequency was set to 2.4 Hz,with the current intensity increased from 450 A to 450 A,the magnetic induction intensity of the stirrer center increased from 405 GS to 520 GS,and the maximum electromagnetic increased from 5.9×10-3 N to 9.7×10-3 N.The maximum axial velocity of the molten steel was increased from 0.13 m/s to 0.18 m/s,and the tangential velocity was increased from 0.44 m/s to 0.56 m/s;When the current intensity was fixed in 350 A,with the frequency increased from 2.0 Hz to 2.4 Hz,the change of magnetic induction intensity was little,and the maximum tangential electromagnetic force was increased from 4.5×10-3 N to 6.8×10-3 N.The maximum tangential velocity of the molten steel increased from 0.40 m/s to 0.48 m/s,the change of axial velocity was little.(5)For the F-EMS,When the frequency was set to 7 Hz,with the current intensity increased from 300 A to 500 A,the maximum value of the axial magnetic induction increased from 312 GS to 527 GS,the radial maximum electromagnetic force increased from 3.93×10-3 N to 1.01×10-2 N,and the maximum tangential velocity at stirrer center increased from 0.11 m/s to 0.23 m/s.When the current intensity was set to 400A,the current frequency increased from 6 to 8 Hz,and the radial maximum electromagnetic force increased from 5,96×10-3 N to 7.98×10-3 N,the maximum tangential velocity of the stirrer center increases from 0.15 m/s to 0.18 m/s,but the influence on the magnetic field intensity was little.(6)Based on the results of the numerical simulation and industrial experiments,the optimal parameters of M-EMS were 450 A and 2.4 Hz;the optimal parameters of F-EMS were 500 A and 7 Hz,respectively.