Investigation On Solute Transport And Inclusion Behavior In Electroslag Remelting Process

Electroslag remelting(ESR)is a secondary refining technique with consumable-electrode used in manufacturing high performance and high added-value materials.It is known that the macrosegregation of solute elements and the amount and distribution of inclusions determine the quality of ingot,so numerical method is employed to investigate the solute transport and inclusion behavior to reveal the formation of macrosegregation,the mechanism of inclusion removal and the inclusion distribution.Based on the finite volume method,a transient fully coupled mathematical model is developed for the multi-physical fields:with the magnetic flux transport of ESR solved,the Joule heating power and the Lorentz force are obtained;the slag-metal interface is tracked with the volume of fraction(VOF)approach;the permeability of mushy zone is defined by Blake-Kozeny equation,and thus the momentum damping in solidification is simulated;The solute redistribution at the solidification front is described by the lever rule,with the consideration of shearing stress,thermal buoyancy and solute buoyancy;the dynamical mesh technique is used to model the ingot growing process.The medium carbon electrode is melt with an experimental scale ESR furnace,the slag temperature,metal pool profile and solute mass fraction are detected in order to validate the model.The calculated results indicate:the positive segregation locates in the center,while the negative segregation in the outer-radius region and the surface of ingot.The solute distribution at the bottom and top of ingot is relatively uniform.Based on Euler-Lagrange approach,a mathematical model for track the unsteady inclusion motion in the melt is also developed.The slag and metal are considered as continuous fluid,while the inclusions are treated as discrete particles,which suffer drag force,surface tension,pressure gradient force,lift force and electromagnetic force,the motion of which is calculated by discrete particle model(DPM).With the VOF-DPM coupled method,the inclusion removal process is revealed,and the calculated removal ratio is validated by the experiment data from by the former research.With the entrapment criterion defined in the model,the inclusion distribution in the ingot is given.The original inclusion removal is determined by the flow of slag.The inclusions in slag hardly enter the molten metal,and rather a few inclusions in metal pool float into the slag.The distribution of original inclusion is determined by the metal pool profile.The inclusions distribute in the region from 1/4 radius to 3/4 radius,while fewer inclusions locate at the surface;the inclusions tend to segregation at the bottom,when the metal pool becomes deeper;due to the finite entrapment ratio,more inclusions locate at the top.The endogenous inclusions distribution is determined by the flow intensity at the solidification front.The inclusions distribute uniformly at the bottom,however,as the metal pool becomes deeper,the inclusion in the outer-radius region of metal pool start to be dragged into molten metal under a more intense flow.Because it is difficult to manufacture large scale electrode when heavy ingot is produced with ESR approach,more than one small electrodes are melt simultaneously.However,the research on multi-electrode system is even less.Thus,a transient model for studying the steady state of multi-electrode ESR system is also developed for the prediction of temperature distribution,flow field and metal pool profile in the industrial apparatus.The results indicate:because heat source and momentum source distribute dispersedly,the temperature is more uniform and the metal pool is much shallower,and a longer distance between electrodes make such effects better;the asymmetric heat source and temperature distribution around the electrode leads to an asymmetric parabolic shape of electrodes,making negative influence on the melting process.