Daniel H. Herring
Vacuum processing is a highly repeatable heat treating method and one that results in optimum surface finish.
Certain types of fastener materials, especially those made from stainless steels and certain superalloy materials, either require or can benefit from processing in vacuum as opposed to using a protective atmosphere. In general, applications involving vacuum heat treating can be broken down into three main categories:…
Source and full article via Fastener Technology International – February/March 2011 : Vacuum Heat Treating Of Fastener Materials.