Abstract
A comprehensive numerical model is proposed to study the influence of an axial magnetic field (AMF) on the solidification behavior of a Titanium-based (Ti–6Al–4V) vacuum arc remelting (VAR) ingot. Both static and time-varying AMF are examined. The proposed 2D axisymmetric swirl model includes calculating electromagnetic and thermal fields in the entire system composed of the electrode, vacuum plasma, ingot, and mold. A combination of vector potential formulation and induction equation is proposed to model the electromagnetic field accurately. Calculations of the flow in the melt pool and solidification of the ingot are also carried out. All governing equations are presented in cylindrical coordinate. The presence of a weak AMF, such as the earth magnetic field, can dramatically influence the flow pattern in the melt pool. The “Electro-vortex flow” is predicted ignoring AMF or in the presence of a time-varying AMF. However, the flow pattern is “Ekman pumping” in the presence of a static AMF. The amount of side-arcing has no influence on the pool depth in the presence of an AMF. Modeling results are validated against experiments.
Highlights
THE vacuum arc remelting (VAR) process is a method of refining a consumable metal electrode to produce various alloys such as stainless steel, Nickel-based, and Titanium-based alloys
The distribution of arc on the surface of ingot, as known as arc radius, and the amount of side-arcing significantly impact the electromagnetic field in the VAR process. Those parameters are kept constant in all simulation trials to study the influence of axial magnetic field (AMF) on magnetohydrodynamics (MHD) in the melt pool
The process comprises a wide range of physical phenomena such as formation and movement of cathode spots on the electrode surface, the vacuum arc plasma, the thermal radiation in the vacuum region, magnetohydrodynamics (MHD) in the melt pool, melting of the electrode, and the solidification of the ingot
Summary
THE vacuum arc remelting (VAR) process is a method of refining a consumable metal electrode to produce various alloys such as stainless steel, Nickel-based, and Titanium-based alloys. Diverse phenomena exist in VAR, including cathode spots at the tip of electrode,[1,2] the vacuum plasma,[3,4,5] the thermal radiation in the vacuum,[6] melting of the electrode,[7,8] solidification of the ingot,[9,10,11] and the interplay between the electromagnetic field and the flow as known as magnetohydrodynamics (MHD) in the melt pool.[12,13,14]. The thermal field and solidification of the ingot is governed by the flow field in the melt pool that in turn is driven by thermosolutal buoyancy and Lorentz force The latter arises from the interaction between the electric current density and both self-induced, axial magnetic fields. Those source terms are extensively described in Reference 31. (v) The arc is implicitly modeled considering a Gaussian distribution of electric current density as a function of radial position on the tip of the electrode and the top of the ingot.[14,32,33,34]
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