Heat Treating Stainless Steel
Heat treating, a process that is used to harden or soften metals by heating and cooling them until they achieve their desired point of hardness, is often performed on stainless steel. In this metal, the structure and composition of the grains, or crystallites, determines its overall mechanical qualities.
Heat treating is an energy-intensive process that changes this atomic structure, therefore changing its mechanical behavior. Steel and stainless steel are the most commonly heat treated metals. During heat treatment, the metal undergoes heating and cooling to change or alter its size, shape and surface. Its mechanical, chemical and physical properties can all be changes as well. Several important techniques are employed during the heat treating process, such as annealing, quenching, tempering and case hardening. Annealing is a process by which a metal is heated and then cooled very slowly, leaving the metal soft and ductile. Quenching on the other hand refers to the rapid cooling of metal and is often used to increase stainless steel's strength. Tempering, in contrast, is performed to strengthen the stainless steel. In tempering, the steel 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 involves 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.
By heat treating stainless steel, improvements can be made regarding its hardness and ductility. The metals tensile, impact and yield strength can also be improved. Stainless steel is made into sheet metal by melting and pressing slabs and rods of steel and alloys into rectangular shapes. Stainless steel is found in three main grades, which are 304, 316 and 410. It can also be found in different gauges ranging from 8 to 30 (where the higher the number, the thinner the metal). Once it is made into the sheets it can undergo additional heat treatment
and fabrication to form it into various products. Many different kinds of equipment, including furnaces, torches, salt bathes, heating blankets, and lasers, are used during the heat treating process. Heat treating is used to make a variety of stainless steel products for the automotive, construction, manufacturing, and tool and die industries, amongst others. Products include car bodies, storage tanks, aircraft panels and ventilation systems.