The process of applying heat to a material to bring about a physical, chemical, or biological change. It is used in the manufacture of glass and metallurgical processes, and can involve heating to very high temperatures as well as chilling to very low temperatures. The heat treatment processes commonly used include annealing, case hardening, tempering, and quenching. The use of heat and time can modify the grain structure of metals leading to improved strength, machinability, and electrical conductance.