Quenching in metalworking is a very specific way of cooling down a metal or an alloy after heat treatment. Depending on the desired characteristics, air cooling slowly may be required, such as in stress relieving treatments, or a more rapid cooling process, or quenching may be used to prevent specific changes in the granular microstructure of the part or component.
The Basics of the Treatment
The process of the quenching heat treatment always involves the application of heat to a specific temperature for a specific amount of time. This first step is determined by the type of metal or alloy and the desired changes. This must be carefully controlled throughout the heating and holding at heat phases of the process.
After the metal or alloy has been heated and maintained at the temperature for the desired duration of time, it is plunged into fresh water, salt water, oil or special polymers which rapidly absorb the heat. It is also possible to use forced air convection to quench a part after heating.
As in the development of the heating process in the quenching heat treatment, the rapid cooling process is also selected based on the desired changes to the metal. As a general rule, the faster the cooling, the harder the final part or component. However, extremely rapid quenching of some metals and alloys can also result in distortions and internal stress.
Knowing how a metal or alloy will react to the stages of the quenching heat treatment will be essential to develop the correct hardness as well as the quality and strength of part required. Different transformational stages can be obtained through the process to fully develop the desired characteristics.
It is not uncommon for quenched steel to then undergo a tempering process. This removes the brittle characteristics of the quenching process while retaining the desired hardening.