Cryogenic treatment uses extremely low temperatures to strengthen metals, eliminating residual stresses and weak spots. It is commonly used in manufacturing automotive parts, castings, and cutting tools. Cryogenic deburring removes sharp edges, while cryogenic hardening promotes a higher percentage of martensite. The music and electronics industries also use cryogenic treatment to improve product quality.
The cryogenic treatment process uses extremely low, or cryogenic, temperatures to treat and strengthen metals. It is generally used to normalize or eliminate residual stresses in a metal part that has been welded or heat treated. Temperatures used in cryogenic processing typically exceed 310° below zero Fahrenheit (about -190° Celsius). Treating metal at these extreme temperatures generally results in a work piece that is more durable, less prone to breakage, and easier to machine into a finished part. Cryogenic processing is used in many industries, but is most common in the manufacturing of automotive parts, castings, and many types of cutting tools.
When a metal part is welded, the heat causes the metal to expand in the area around the weld. As the part cools, it contracts unevenly, leaving behind residual stresses and potential weak spots. The same is true for heat treatment and other processes that induce high temperatures in the metal. The extremely cold temperatures employed in cryogenic processing relieve these stresses and eliminate weak spots in the part promoting uniform shrinkage and altering the grain of the alloy. Common cryogenic processing practices include cryogenic deburring and cryogenic hardening.
Deburring is the process of removing sharp edges caused by machining or the burr that builds up when a part is cast or forged. In cryogenic deburring, a part is usually cooled with liquid nitrogen to cryogenic temperatures. Extreme cold makes burs and flashes brittle, making them easy to remove by shot blasting or tumbling. Because they are soft and difficult to work with at room temperature, plastic and rubber parts are also often cryogenically deburred.
When a metal part is heat treated, a crystalline structure, called austenite, transforms into a differently shaped grain, called martensite. Since some standards require more martensite than is normally produced by heat treatment, the transformation is often extended by cryogenic hardening, which is usually done at temperatures of -300°F (-185°C) and lower. This type of cryogenic treatment causes a rapid change in the structure of the alloy, resulting in a higher percentage of martensite.
The music and electronics industries have also found ways to improve the quality of their products through cryogenic treatment. Cryogenic treatment of a brass instrument, such as a trumpet or saxophone, is believed to relieve residual stresses created during manufacturing, resulting in better overall vibration and better intonation. Steel guitar strings and electronic components, such as cables and stereo connectors, are also said to show better performance after undergoing cryogenic treatment.
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