Vacuum Induction Melting Furnace Design
Vacuum induction melting is indispensable in the manufacture of superalloys. Compared to air-melting processes such electric arc furnaces (EAF) with argon oxygen decarburization (AOD) converters, VIM of superalloys provides a considerable reduction in oxygen and nitrogen contents. Accordingly, with fewer oxides and nitrides formed, the microcleanliness of vacuum- melted superalloys is greatly improved compared to air (EAF/AOD)-melted superalloys.
Additionally, high-vapor-pressure elements (specifically lead and bismuth) that may enter the scrap circuit during the manufacture of superalloy components are reduced during the melting process. Accordingly, the vacuummelted superalloys (compared to EAF/AODmelted alloys) are improved in fatigue and stress-rupture properties.
Control of alloying elements also may be achieved to much tighter levels than in EAF/AOD products. However, problems can arise in the case of alloying elements with high vapor pressures, such as manganese. Vacuum melting also is more costly than EAF/AOD melting.The EAF/AOD process allows compositional modification (reduction of carbon, titanium,sulfur, silicon, aluminum, etc.). In vacuum melting, the charge remains very close in composition to the nominal chemistry of the initial charge made to the vacuum furnace. Minor reductions in carbon content may occur, and most VIM operations now include a deliberate desulfurization step. However, the composition is substantially fixed by choice of the initial charge materials, and these materials are inevitably higher-priced than those that are used in arc-AOD.
Edited by Jessica
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