Definition - What does Quenching mean?

Quenching is the soaking of a metal at a high temperature, above the recrystallization phase, followed by a rapid cooling process to obtain certain desirable material properties.

Depending on the circumstances in which metals are being used, they are usually quenched at the time of processing, and polymers may also be quenched. The quenching of steel creates martensite.

It is usually undertaken to maintain mechanical properties associated with a crystalline structure or phase distribution that would be lost upon slow cooling. This method is commonly applied to steel objects, to which it imparts hardness. On the other hand, copper objects that have become hardened by hammering or other deformation at ordinary temperatures can be restored to a malleable state by heating and quenching. It also increases toughness of both alloys and plastics.

Corrosionpedia explains Quenching

Quenching is a stage of material processing through which a metal is quickly brought down to room temperature from a high temperature by rapid cooling. Quench hardening is a mechanical process in which steel and cast-iron alloys are strengthened and hardened. Quenching and tempering provides steel with high strength and ductility.

During quenching, the following media are used to rapidly cool material:

  • Air/argon/nitrogen
  • Liquid polymers
  • Oil
  • Water

The slower the quench rate, the longer thermodynamic forces have to alter the microstructure, which is in some cases desirable, hence the use of different media. Sometimes multiple media are used. For example, metal may be air cooled and then dipped in a water bath to complete the quenching process.

Quenching can lead to warping/cracking and other issues with the material, even when it is done properly. Using water as a quench media, for instance, can cause the material to warp as it cools. It is crucial to control the environment in which the quenching is done to minimize the risk of damage to the material. When done properly, the material is harder and more durable, making it suitable for a wide range of uses. Extremely rapid cooling can prevent the formation of a crystal structure, resulting in amorphous metal or "metallic glass."

Four types of furnaces are commonly used in quench hardening:

  • Salt bath furnace
  • Continuous furnace
  • Box furnace
  • Vacuum furnace

The type of furnace used depends on what other processes or types of quench hardening are being done on the different materials.

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