Heat treating services are commonly sought when a manufacturer needs to change the hardness of metallic or glass material through controlled heating and cooling. There are three main processes that can be used to when heat treating: annealing, which decreases the hardness of metals so that they can be easier to form (and can sometimes relieve stress as well); hardening, which makes the material being treated stronger; and tempering, which involves reheating the material to a temperature well below the hardening stage so as to reduce stresses and further strengthen it.
Annealing is one of the heat treating services that is used to soften steel and other metals. It can be used to relieve stress that has been caused by uneven cooling or other treatment. Additionally, it is used to soften steel to improve formability. The process of annealing involves heating the metal to a certain temperature, then soaking the metal at a level of heat for a predetermined time, and finally, cooling the material at a particular rate. This heat treatment is used on cold-worked sheets, castings and forgings.
Hardening is another of the many heat treating services used on metals. As the name implies it serves to toughen and improve the strength of the metal being treated. How hard a metal can become depends on how much carbon is contained in the sample. Carburizing, or adding carbon to the surface of low-carbon steels, can be effective when the metal is quenched, or cooled rapidly to form martensite, which coats the metal and makes it sturdier. Wrought iron, which contains no carbon, is unhardenable. The process of hardening varies depending on the type of material, but in general, it involves heating the metal to a point just above the “transformation point,” where the metal then becomes non-magnetic. Then it is quenched in salt or plain water, oil or air. After that, the metal is tempered by reheating to avoid brittleness.
Tempering is a method used by metallurgic workers to ensure that the treated metal does not become brittle and unstable. It is done by reheating the metal, oftentimes steel, to a temperature high enough to affect it but not so high that it hardens. To temper metal it must be heated to a temperature between 350°F to 1400°F depending on the type of metal being used. On important parts, double tempering is often recommended.
Heat treating services vary by product and desired result. New advances are allowing even more ways to treat metal, including cryogenic cooling (the soaking of product in liquid nitrogen) and differential hardening, whereby different areas of the metal are heated and cooled at different rates.
