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An Overview of Cryogenic Hardening for Metal

  • July 16, 2019

Metals like steel, iron, copper and aluminum are often heat treated to improve their physical properties. When metal is exposed to heat, it undergoes a chemical reaction in which its atoms expand. Normally, heat treatment is performed in conjunction with cooling. After the metal has been heated, it’s rapidly cooled to achieve more desirable properties like increased strength and durability. Cryogenic hardening, however, is a unique metal treatment process in which metal is intentionally exposed to extremely cold temperatures.

What Is Cryogenic Hardening?

Cryogenic hardening is a metal treatment process that’s characterized by the use of liquid nitrogen to freeze metal. While temperatures vary, it’s not uncommon for metal to reach -301 degrees Fahrenheit during this process. At cold temperatures such as this, the amount of martensite in the treated metal increases, resulting in some unique benefits that aren’t found in other treatment processes.

How Cryogenic Hardening Is Performed

To perform cryogenic hardening, metal is first exposed to heat using a conventional heat treatment process. Next, the metal is slowly cooled using liquid nitrogen. Once the metal is submerged or otherwise exposed to liquid nitrogen, its temperature begins to drop. The metal is held at a stable, cool temperature for up to 24 hours, after which it undergoes a second round of heat treatment to minimize brittleness.

Benefits of Cryogenic Hardening

Although it’s somewhat complex and technical process, cryogenic hardening offers several benefits, one of which is increased strength. When the temperature of metal drops, its atoms rearrange in a manner that increases the metal’s martensite and decreases the metal’s austenite. Martensite, of course, is an incredibly hard crystalline structure, whereas austenite is soft and ductile.

Cryogenic hardening is able to make metal objects and workpieces more resistance to wear and tear. Metal doesn’t just become harder through cryogenic hardening; it becomes tougher and more resistant to wear. As a result, cryogenic hardening is performed to increase the usable life of metal objects and workpieces.

Furthermore, cryogenic hardening offers stress relief of metal. When metal is exposed to heat and then rapidly cooled, stresses are created. Cryogenic hardening, however, can eliminate these stresses to achieve a uniform composition.

It’s also worth mentioning that cryogenic hardening supports a variety of metals. While it’s most commonly performed on steel, it can be performed on iron, copper, aluminum, magnesium and other metals as well. These are just a few of the most noteworthy benefits of cryogenic hardening.

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