A modified volume-of-fluid method is implemented in a fixed-grid, finite-volume model simulating transport phenomena, solidification, and electromagnetics. The VOF model agrees well with published results, and the complete model is used to investigate process variations in the electroslag remelting process, in which liquid metal is melted from a consumable electrode immersed in an electrically resistive slag. The molten metal sinks through the slag cap floating on the liquid metal pool while a slag skin freezes to the mold. Here a VOF tracks slag skin formation and its effects on melt rate with different current levels and ingot diameters.

Simulation of Slag-Skin Formation in Electroslag Remelting Using a Volume-of-Fluid Method

Most conventional electroslag remelting (ESR) processes are operated with AC current, but the inductive loss of the power becomes a major problem when the process is operated at the high frequency for large scale ESR. Nowadays, the demand on large scale ingots has driven the people to think of operating the process with AC current at low frequency. Here the influence of the applied frequency of AC current on the large scale ESR process is numerically investigated. For this purpose, simulations with two operating AC frequencies (0.2 and 50 Hz) are performed. The main goal is to achieve some fundamental understanding of the two-phase flow and the formation of melt pool of the solidifying ingot under the influence of AC frequency. As we also know that the mold current (portion of electric current entering through solid slag skin into the mold) plays an important role in the process, calculations considering different current paths are also analyzed.

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A Numerical Study on the Influence of the Frequency of the Applied AC Current on the Electroslag Remelting Process

Electroslag remelting (ESR) is a secondary melting process used to cast stainless steel and superalloy ingots. In this process, current flows through a consumable electrode immersed in an electrically resistive slag, providing the heat to melt the electrode. Droplets from the electrode sink through the slag, pooling at the bottom of the mold and forming the final ingot. The electrode melt rate is a key parameter, affecting the probability of surface and macrosegregation defects. This work uses an axisymmetric model to simulate flow, heat and mass transfer, solidification, and electromagnetics in the production of industrial scale ESR ingots. The simulated melt rate, sump shape, and surface defects are qualitatively similar to measured data. However, quantitative comparisons are difficult to obtain due to large uncertainty in slag properties and lack of electrode motion in the present model.

Predicting Melting Behavior of an Industrial Electroslag Remelting Ingot

A better understanding of droplet formation and dripping behavior would be useful in the efficient removal of impurity elements and nonmetallic inclusions from liquid metals. In the present work, we developed a transparent experimental apparatus to study the mechanisms of droplet formation and the effects of filling ratio on droplet behavior during the electroslag remelting (ESR) process. A high-speed camera was used to clearly observe, at small time scales, the droplet formation and dripping phenomenon at the slag/metal interface during a stable ESR process. The results illustrate that a two-stage process for droplet formation and dripping occurs during the ESR process and that the droplet diameter exhibits a parabolic distribution with increasing filling ratio because of the different shape and thermal state of the electrode tip. This work also confirms that a relatively large filling ratio reduces electricity consumption and improves ingot quality.

Research on droplet formation and dripping behavior during the electroslag remelting process

In electroslag remelting (ESR), the slag generates heat, chemically refines the melting electrode material, and forms frozen skin on the mold. An axisymmetric model is used to simulate fluid flow, heat transfer, solidification, and electromagnetics and their interaction with slag skin formation in ESR. A volume of fluid (VOF) method is used to track the slag/metal interface, allowing simulation of slag freezing to the mold. Mold diameter and applied current are varied to determine how these parameters affect melt rate and formation of slag skin during ESR. Variations in the slag skin thickness within the slag cap are found to have a significant impact on melt rate and depth of metal sump. Changes in slag cap volume resulted in small changes in melt rate.

A Parametric Study of Slag Skin Formation in Electroslag Remelting

In the present paper, the droplet formation during melting of a 420 mm diameter flat electrode is simulated with an advanced three dimensional multiphase-Magneto-hydrodynamic numerical model. The momentum, energy and electromagnetic fields are fully coupled. The computational domain includes a layer of slag and a layer of liquid steel. A VOF approach is used for the interface tracking and a potential formulation is used for the electric and the magnetic field. It is shown that a complex interaction between the electromagnetic field and the phase distribution occurs. This interaction generates a strong 3D flows that cannot be predicted with conventional 2D models.

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Franz-Joseph Strasse

Papers

3d simulation of the melting during an industrial scale electro-slag remelting process