This article focuses on various vacuum heat treating processes for additively manufactured parts, namely annealing and stress relieving, solid-solution annealing, and solution treating and aging. It addresses several practical concerns involved in using vacuum heat treatment, including temperature measurement, unvented cavities, loose powder, and direct contact of metals in the high-temperature vacuum. The article provides a short discussion on sintering and evaporation of metals in vacuum furnaces.

Vacuum heat treating consists of thermally treating metals and alloys in cylindrical steel chambers that have been pumped down to less than normal atmospheric pressure. This article provides a detailed account of the operations and designs of vacuum furnaces, discussing their pressure levels, resistance heating elements, quenching systems, work load support, pumping systems, and temperature control systems. It describes the classification of instruments used for measuring and recording pressure inside a vacuum processing chamber. Common devices include hydrostatic measuring devices and devices for measuring thermal and electrical conductivity. The article also describes the applications of the vacuum heat treating process, namely, vacuum nitriding and vacuum carburizing. Finally, it reviews the heat treating process of tool steels, stainless steels, Inconel 718, and titanium and its alloys.