Editing Cryogenics (section)

=== Cryogenic processing ===
The field of cryogenics advanced during World War II when scientists found that metals frozen to low temperatures showed more resistance to wear. Based on this theory of [[cryogenic hardening]], the commercial [[cryogenic processor|cryogenic processing]] industry was founded in 1966 by Bill and Ed Busch. With a background in the [[heat treating]] industry, the Busch brothers founded a company in [[Detroit]] called CryoTech in 1966.<ref>{{cite book|last1=Gantz|first1=Carroll|title=Refrigeration: A History|date=2015|publisher=McFarland & Company, Inc.|location=Jefferson, North Carolina|isbn=978-0-7864-7687-9|page=227|url=https://books.google.com/books?id=0UgjCgAAQBAJ&q=ed+busch+cryotech&pg=PA227}}</ref> Busch originally experimented with the possibility of increasing the life of metal tools to anywhere between 200% and 400% of the original life expectancy using [[cryogenic tempering]] instead of [[heat treating]].<ref>{{Cite book |last=Zohuri |first=Bahman |title=Physics of Cryogenics: An Ultralow Temperature Phenomenon |publisher=Elsevier |year=2018 |isbn=978-0-12-814519-7 |pages=34 |chapter=Chapter 1 - Cryogenic Technologies |doi=10.1016/C2017-0-01796-2}}</ref> This evolved in the late 1990s into the treatment of other parts.

Cryogens, such as liquid [[nitrogen]], are further used for specialty chilling and freezing applications. Some chemical reactions, like those used to produce the active ingredients for the popular [[statin]] drugs, must occur at low temperatures of approximately {{convert|−100|°C|°F}}. Special cryogenic [[chemical reactor]]s are used to remove reaction heat and provide a low temperature environment. The freezing of foods and biotechnology products, like [[vaccine]]s, requires nitrogen in blast freezing or immersion freezing systems. Certain soft or elastic materials become hard and [[brittle]] at very low temperatures, which makes cryogenic [[mill (grinding)|milling]] ([[cryomilling]]) an option for some materials that cannot easily be milled at higher temperatures.

Cryogenic processing is not a substitute for heat treatment, but rather an extension of the heating–quenching–tempering cycle. Normally, when an item is quenched, the final temperature is ambient. The only reason for this is that most heat treaters do not have cooling equipment. There is nothing metallurgically significant about ambient temperature. The cryogenic process continues this action from ambient temperature down to {{convert|-320|°F|°R K °C|0}}.
In most instances the cryogenic cycle is followed by a heat tempering procedure. As all alloys do not have the same chemical constituents, the tempering procedure varies according to the material's chemical composition, thermal history and/or a tool's particular service application.

The entire process takes 3–4 days.