Heat Treating Steel
Steel heat treating is a process that is used to harden or soften steel by heating or cooling the metal until it reaches the desired point of hardness. In steel, like all metals, the structure and composition of the grains, or crystallites, determines the overall mechanical qualities of the metal. Heat treatment can be used to alter the chemical, physical and mechanical behavior of the metals.
Heat treating is an energy-intensive process that changes this atomic structure, thereby also changing its mechanical behavior. Although many metals go through the process, steel is the most commonly heat-treated metal. Other popular metals include aluminum and stainless steel. Several critical techniques are used in the steel heat treating process, including annealing, quenching, case hardening, precipitation strengthening, and tempering. Annealing is a process by which steel is heated and then cooled very slowly, leaving the soft, ductile metal. Quenching refers to the rapid cooling of steel that can be used to increase the metal's strength. Tempering is also performed to strengthen steel; in tempering, the metal is heated to extreme heat, between 400 and 600 degrees Celsius, and maintained at this temperature until the carbon diffuses to produce bainite or pearlite. Case hardening is accomplished by combining the ductility of low carbon materials with the strength of high carbon through the creation of a tough outer coating which surrounds a softer more malleable core. Precipitation strengthening is a process that increases the yield strength of the metal, this can also be referred to as age hardening.Heat treating steel can improve the metals hardness and ductility. It can also improve the metals tensile, impact and yield strength. Many different kinds of equipment are used in the heat treating process. Some of these tools include furnaces, torches, salt bathes, heating blankets and lasers. Due to the fact that many of the products are custom and specialty made, there is no one correct way of heat treating metals. There is always a high demand for the products though. Heat treating is used to make a variety of steel goods used in the automotive, air transport, construction, manufacturing, and tool and die industries. Some examples of heat-treated steel goods include knives, swords, gears, medical equipment, valves, drive shafts, ventilation systems and bearings.