| The macrosegregation phenomenon caused by the large size of ingot cannot be eliminated,which seriously affects the quality of ingot.In this paper,the macrosegregation phenomenon of large H13 electroslag remelting die steel is studied and a three-dimensional unsteady electroslag remelting mathematical model is established.Based on mxwell’s equations,a magnetic vector potential is introduced to calculate the joule heat and lorentz force,which is coupled to the energy and momentum equations by user-defined functions.The growth process of ingot was realized by moving grid technology,The VOF model is used to track the slag/gold interface.The anisotropic porous media model is used to simulate the momentum attenuation in the mushy zone.And solute redistribution behavior was calculated by Lever algorithm.The accuracy of the mathematical model is verified by experiments.The shape of the molten pool,the temperature field,the flow field and the macrosegregation of carbon element in the process of ESR were studied.The effects of constant power and constant melting rate processes on the macrosegregation of carbon elements are compared,and the effects of the initial mass fractions of carbon,silicon,and molybdenum on the macrosegregation of carbon elements are analyzed.So as to provide a new idea for reducing the macroscopic segregation of carbon element in the ESR process of large H13 hot working die steel.The results show that the Joule heat is mainly concentrated in the slag layer,the maximum Joule heat is on both sides of the electrode end,and the minimum Joule heat is near the slag layer in the upper part of the mold.The high temperature zone in the furnace is also concentrated in the slag layer,and the temperature distribution under the slag/gold interface is more uniform.An electromagnetic force directed at the center of the mold is generated on the side of the consumable electrode tip,which is conducive to the formation of droplets.In the slag pool,there are a pair of streamline lines with opposite movement direction,which are respectively generated at the end of the consumable electrode and the side wall of the mold.Under the action of Lorentz force and gravity,an anticlockwise movement streamline is formed under the consumable electrode.At the side wall of the mold,in the gravity and viscosity under the action of shear force,a flow line moving clockwise is formed.Carbon elements are mainly concentrated in the center of ingot,less in the bottom and edge,and the concentration gradient distribution of carbon elements is more uniform.Through experiments,the maximum carbon segregation index error between simulation results and experimental results is within 7%,which verifies the accuracy of the numerical model.Carbon element shows negative segregation at the bottom and edge of the ingot and positive segregation along the axis of the ingot.Reducing the initial mass fraction of carbon element(0.45%,0.32%)within the standard composition of H13 steel can reduce the macro segregation of carbon element in steel ingot.The maximum positive segregation index of carbon element decreased from 0.0837 to 0.0787,with a decrease of 5.97%.Increasing the initial mass fraction(0.8%,1.2%)of silicon within the standard composition of H13 steel would increase the macrosegregation of carbon,and the maximum positive segregation index of carbon increased from 0.0817 to 0.0887,an increase of 8.56%.Increasing the initial mass fraction of molybdenum within the standard composition of H13 steel(1.1%,1.75%)can reduce the macro segregation of carbon in ingot,and the maximum positive segregation index of carbon decreases from 0.0795 to 0.0780,decreasing by 1.88%.Under the condition of decreasing the initial mass fraction of carbon and increasing the initial mass fraction of silicon and molybdenum,the distribution of carbon can be more uniform.Through the analysis of the working current,it can be known that increasing the working current will increase the segregation degree of carbon element.At the beginning of remelting,the consumable electrode with gradually decreasing mass fraction of carbon element reduced the macrosegregation of carbon element,and the maximum positive segregation of carbon element decreased from 0.0837 to 0.0797,down 4.78%.Under the condition of constant melting rate,the temperature of slag pool is relatively low,the temperature distribution in the pool is more uniform,the shape of the pool is relatively flat,and the macro segregation of carbon element is reduced.The maximum positive segregation of carbon element is reduced from 0.0837 to 0.0817,down 2.39%.To sum up,a complete three-dimensional unsteady electroslag remelting mathematical model was established in this study,and the heat distribution,temperature distribution,lorentz force,flow field,molten pool shape and the macro segregation of carbon element in the process of electroslag remelting were obtained.The optimization of the process parameters and the change of the initial alloy element mass fraction can improve the uneven distribution of the macro elements of the carbon elements in the H13 steel and reduce the macro segregation of the carbon elements.This provides a new idea for reducing the macro segregation of elements in large electroslag remelted steel ingots. |
