Glossary

Vacuum induction melting (VIM) is a metallurgical melting process where metal is melted by electromagnetic induction inside a sealed vacuum chamber. An induction coil surrounds a refractory-lined crucible; alternating current in the coil induces eddy currents in the charge, heating and melting it—while the surrounding vacuum minimizes reactions with air.

In practical plant terms, the “vacuum” part is the whole point: by removing air, VIM greatly reduces oxidation and contamination and supports degassing (lowering dissolved gases like hydrogen and nitrogen). That makes it well suited to alloys where chemistry control and cleanliness matter—especially when reactive elements are involved and where dissolved gases or inclusions would wreck fatigue life, toughness, or high-temperature performance.

A typical VIM cycle looks like this: you load carefully selected charge materials into the crucible, pull vacuum, melt via induction, and then refine/adjust chemistry while the bath is molten (additions, deoxidation practices, degassing/volatile control), followed by casting into molds/ingots or transferring the melt to a downstream process. It’s common for VIM to be used as a primary melt step for high-quality alloys and then be followed by remelting processes (depending on the product requirements).

VIM is widely associated with high-performance alloys (notably nickel-based alloys/superalloys) and other “tight chemistry” materials used in demanding sectors like aerospace and nuclear, where internal cleanliness and repeatability are non-negotiable.

It’s also useful to distinguish VIM from the remelt processes you’ll see in premium specs. VIM is often the primary melting and chemistry-control step; processes like vacuum arc remelting (VAR) are commonly used as secondary remelting to further improve ingot quality/homogeneity and reduce defects/inclusions relative to air-melt alone.