Transport phenomena and modelling in melting and refining processes

Abstract
Increasing requirements for ultra pure metallic materials with greater reliability and more reproducible mechanical properties have led over the years to a continual endeavour to improve the control of composition and inclusion contents (nitrides, oxides, carbides, etc.) in cast products. This is illustrated by melting and refining processes such as Vacuum Induction Melting (VIM), Vacuum Arc Remelting (VAR), Electro Slag Remelting (ESR), Electron Beam Melting (EBM) and Electron Beam Cold Hearth Remelting (EBCHR). The materials involved are nickel-base superalloys, specialty steels, refractory metals such as tantalum, niobium, tungsten and molybdenum, and the reactive metals hafnium, zirconium and titanium, together with their alloys. The mastery of these refining processes requires a perfect knowledge of the physical-chemical phenomena involved, including both thermodynamic aspects and transport mechanisms within the liquid metal and at the interfaces (particularly that between the melt and the vacuum or gaseous phase), together with the behaviour of inclusions. Examples are described to show how this knowledge of the basic phenomena can be combined with process modelling to improve the control of product quality.