There are various types of annealing processes that can be carried out depending on the material and results required.

Full Annealing involves taking the material above its recrystallisation point then cooling at a suitable rate to ensure the transformation of the crystal structure results in a softer more ductile material.
Intermediate and Subcritical annealing cause little or no change in the crystal structure of the material, restoring some ductility
Normalisation is designed to improve the uniformity of the crystal structure of the steel, particularly after forging or casting where undesirable large crystal microstructures can form that negatively impact the physical properties.
Other common metals such as copper and aluminium can also benefit from annealing processes.
The high magnetic permeability of MuMetal is created by annealing in a hydrogen furnace, and following machining/welding this can be restored by annealing in vacuum.
Though not always strictly necessary, we anneal all parts in vacuum to ensure they are processed in highly controlled, repeatable environment, delivering first-rate results every time.