Macrosegregation During Electroslag Remelting of Alloy 625
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TRODUCTION
ELECTROSLAG remelting (ESR) is used to enhance the metallurgical structure and refine the chemistry of an ingot.[1] This process places a consumable electrode in contact with electrically resistive ceramic slag. Joule heating causes the slag to remelt the electrode, and melted metal droplets pass through the less dense slag and solidify in the water-cooled crucible below (Figure 1). Because of the complexity of the process and the difficulty and expense of experimental work with it, several numerical models have been developed in the past decade to gain insight into the ESR process. A group at Innovative Research, Inc., (IRI) developed a steady-state model of the ESR process for cylindrical ingots capable of predicting fluid flow, electromagnetics, temperature fields, and parameters of interest such as local solidification time, cooling rate, and dendrite arm spacings.[2] They used a j-e model for turbulent flow in the slag and molten pool, where natural convection in the metal pool was driven solely by thermally induced density differences. This model was used to predict how the power input affects the liquid metal pool shape and size during steady-state melting of alloy 718 in good agreement with experiments at low melt rates.[2–4] More recently, this group has developed a transient ESR model for cylindrical ingots. The model includes the
KYLE FEZI, Graduate Research Assistant, and MATTHEW JOHN M. KRANE, Associate Professor, are with Purdue Center for Metal Casting Research, School of Materials Engineering, Purdue University, 701 West Stadium Avenue, West Lafayette, IN 47906. JEFFREY YANKE, Formerly Graduate Research Assistant, the Purdue Center for Metal Casting Research, School of Materials Engineering, Purdue University, is now with the Carpenter Technology Corporation, Reading, PA. Contact e-mail: [email protected] Manuscript submitted October 20, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
same physics as the previous model, with the addition of a hot-slag start, hot-topping, and slag solidification.[5] A fully transient ESR process model has been developed by Weber et al. including the same physics as the IRI model.[6] The continuous growth of the ingot was simulated by a mesh-splitting method. Solidification of both metal and slag is modeled, in which the solidification paths were determined by commercial thermodynamic software. A simple slag solidification model was used to predict the slag skin thickness and its contribution to thermal loss through the crucible walls.[6, 7] These thickness calculations were compared to experimental data, in good agreement with the overall trend but the values were over-predicted by nearly a factor of two.[7] Predicted pool profile shape and depth were compared to the experimental pool markings and showed good agreement at two different melt rates.[6] A third group has studied the behavior of the slagmetal interface during the ESR process using an axisymmetric steady-state model.[8] This model focused on the prediction of the shape of the slag-liquid metal interface, usin
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