| Electroslag remelting(ESR) is a metallurgial technology with the metal refining and purification, solidification and forming crystals in one mould. The process contains many complicated physical and chemical reactions such as the coupling of multi-field including electromagnetic, flow, heat transfer, solidification and so on.With the increasing demands of industrial production, the life span and the mechanical properties of high-quality special steel need to be improved. Despite segregation, coarse microstructure, shrinkage porosity and other issues exist in the ingot producted by ESR, it has a significant improvement in quality compared with ordinary casting products. To metallurgy workers, the next goal is to solve the problems that still exist in ESR technique. With the increasing demands of high-parameter, high-capacity equipment, large forgings production are of catholic concern.Multi-electrode (double, triple and six electrodes) remelting ingots become popular. The analysis of electromagnetic field, temperature field and solidification play an important role as the guide for technological operation and ingot quality. In this paper, using the numerical methods, multi-field, like electromagnetic fields, Joule heat, and temperature field which are difficult to measure were studied. And the transient electromagnetic field was studied in detail which few literature mentioned. The study will provide a theoretical basis for multi-electrode remelting processes,.The main research topics:(1) Based on the previous basis of steady-state ESR process and harmonic results, create a single electrode remelting system described in electromagnetic fields, Joule heating field and temperature field model. At first, using MFS solver coupling method, harmonic electromagnetic field and temperature fields were calculated. And then trasient electromagnetic field analysis and Joule heating field were studied in the single electrode remelting electrode system, slag pool, the pool and the metal ingot by sequential coupling method.(2) The mathematical model was built which could discrebe electromagnetic field, Joule heating field and temperature field in two series-connected ESR system to calculate the distribution of transient electromagnetic field. (3) The mathematical model was built which could discrebe electromagnetic fields, Joule heating field and temperature field in three-phase three-electrode ESR system to calculate the distribution of transient electromagnetic field.(4) The mathematical model was built which could discrebe electromagnetic fields, Joule heating field and temperature field in three-phase six-electrode ESR system to calculate the distribution of transient electromagnetic field.The research concluded:(1) In single-electrode ESR systems, the current density distribution of the vectors vary at different moment.The electromagnetic field generated by current generates current simultaneously. Vortex current was induced at90degrees and270degrees phase which becomes the main current source. The skin effect is not shown in single-electrode system at each moment in consideration of the strongly transient changes in current load.The change of magnetic flux density in ingot lag behind that in slag. Electromagnetic force variation period is1/2cycle of the AC load.The axial component of electromagnetic force in slag exist continuously, which has impact on the flow of molten steel and slag. When phase is0, the most Joule heat is generated.(2) In two series-connected ESR systems, the current density distribution of the vectors vary at different moment.The main flow path of current are located in the top of slag layer and the interface between slag and metal. When phase is0or180degrees, current in the path of slag is stronger than that in interface. However, at90or180degrees, the opposite result is shown, and the lower path of current is vortex. In the slag between two main path, the current flow direction changes dramatic with time. Variability of the flow path is benefit to uniform distribution of Joule heat and temperature field. In the slag layer the electromagnetic force always contains axial component. In the center of the slag layer, the electromagnetic force vertically downward.The main area generating Joule heat alternate in the bottom of the two electrodes over time.(3) The more complicated current density distribution exists in a three-phase ESR system. The current path is divided into two paths in cross section of interface.One path is short and and has large flux. The other current path is long and has small flux.Position of the two paths change clockwise with the growth of phase growth.Induction magnetic field gathered in the center of the slag vary over time. In the two main current path, the electromagnetic force is larger than other position, and the direction is always down. The main area generating Joule heat alternate in the bottom of the several electrodes over time. |
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