Heat treating refers to a group of thermal, industrial, and metalworking processes that change either the physical or chemical properties of a material. The heat treatment process affects the structure of the material being heated. Most carbon steels and carbon steel alloys can be heat treated to improve qualities like tensile and yield strength. Some specific heat treatments of metals include annealing, normalizing, hardening, and quench & tempering.
Annealing
Annealing is a heat treating process specifically used to increase the ductility and reduce the hardness of a material. During the process, the manufacturer heats the metal and then allows it to cool slowly. This process helps to remove internal stresses making the material easier to work. Certain metals are annealed to increase the electrical conductivity of the materiall. It is an important process in maintaining ductility and reducing hardness after cold working.
Normalizing
Normalizing is another heat treatment of metals, often used when producing steel and steel products. During this process, the material being treated is heated to a predetermined temperature and then held at that temperature for a certain amount of time (usually between 10 to 20 minutes). The purpose of the normalizing process includes removing structural irregularities or impurities, improving ductility, reducing hardness, increasing toughness, relieving internal stresses, and increasing machinability.
Hardening
Hardening is a metallurgical metalworking process used to increase the hardness of metal, particularly steel. This process is usually carried out on finished products and not raw materials. The process is often done on machined parts since hardening a whole block of steel is not economical. Hardened steel is also more difficult to machine, resulting in shorter lifespans of tools and attachments. The hardness of a metal is proportional to the uniaxial yield stress at the location of imposed strain. Harder metals have a higher resistance to plastic deformation, therefore, may be better to use during certain processing procedures.
Quenching and tempering
Quenched and tempered steel is an abrasion-resistant steel that is high in strength, fabrication qualities, and mechanical properties. Production involves heating materials to a certain temperature, coupled with specific cooling speeds and methods. This "quenching" process immediately cools the heated material in water, oil, and forced air or inert gasses such as nitrogen. These two processes result in harder and tougher finished products.