What is external quenching?

External quenching refers to the process of rapidly cooling a material, typically metal, from a high temperature to a much lower temperature using an external medium, such as water, oil, or air. This technique is often used in heat treatment to enhance the mechanical properties of materials, such as increasing hardness and strength. The quenching process can also lead to the formation of specific microstructures, which can significantly affect the material's performance. However, improper quenching can result in thermal stresses and cracking.