Metals react in their own typical way when they are heated to a specific temperature and let to cool down. Application of heat typically improves their qualities. They become harder and more qualified to be used in building skyscrapers and other buildings. This could also be done to glass. Heat could also be used to soften the material using high or low temperatures. A lot depends on the final temperature to which the material is heated, and the time period for which it is heated or subject to such a treatment. We have been using the process of welding as a corollary to the heat treatment process to bring two elements together for a long time. The process is merely an extension of the knowledge we possessed ever since we learnt to use fire and heat with metals. All of it boils down to the truth that heat changes some properties of metals.
The process targets the knowledge that each element is composed of minute atoms that are sensitive to heat and energy. Heating of metals results in the expansion of these atoms, whereby they require more space to exist. Heating the elements to certain temperatures results in change in their mechanical properties. Metals could be subjected to certain processes to achieve these ends:
- Quenching
- Annealing
- Precipitation Hardening
Steel could be hardened by exposing it to a high temperature before it is immersed in oil or salted water or plain water at room temperature. This freezes the crystal structure within steel. The process is known as quenching. An alternative arrangement involves using a cooling bath with temperatures ranging from -180 to -70 degrees Centigrade. Steel thus obtained finds use in the treatment of high-alloy and high-carbon steels.
Under quenching, metals are heated to high temperatures and let to cool down at once. The rate of cooling usually depends on the metal on which the process is applied. Different methods are applied for different metals, anything like water or liquid nitrogen could be used. Quenching is usually used for cast iron or steel.
Annealing involves heating the element and letting it cool down at a rate of 20 degrees Celcius per hour. Normal air at room temperature could be used to bring temperatures down. Annealing usually results in softening of the material to enable it to be modified into another shape. Heating changes the distribution of the crystals within the metal besides affecting their size and shape. Annealing is of different sorts depending on the temperature to which the metal is heated:
- Process Annealing
- Stress Relief Annealing
- Spheroidization
- Normalizing
- Full Annealing
Annealing and tempering are the two methods used generally to restore a metal's ductility. The temperature is raised to a certain point, when resorting to annealing, and let to come down to a low point after some time. Tempering involves heating the element by maintaining it in an oil bath for a little while.
Precipitation Hardening, also known as age hardening, is used to lend strength to alloys of metals. This is used for hardening stainless steel and titanium. The temperature to which the alloy is heated decides the strength of the resulting material. For each element, there is a specific temperature that is set for lending the most strength to the metal.
