Heat treatment is the process of modifying a metal’s mechanical properties, such as strength, brittleness, machinability, and hardness. Heat treating changes metal properties by heating the metal to a specific temperature, holding it at that temperature for a certain length of time, and then using one of several methods to control the cooling of the metal. A metal’s properties are determined by the shape and alignment of its atoms. These atoms are arranged in three-dimensional patterns called crystalline structures. Heat treating works by altering the shape and alignment of a metal’s crystalline structure.

The changing of the metal’s properties occurs when a metal is heated to a high temperature. The temperature, which remains below the material’s melting point, excites the atoms of the metal allowing its crystal structure to change. Heat treating can be used to make a material harder or softer. An example of a product that requires heat treating to harden its material is a steel chisel. During heat treatment, the chisel is heated to a specific temperature range, which changes its crystal structure and increases its hardness.