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Tempering is a process that dates back thousands of years, and the theory behind it has remained relatively unchanged in the centuries since. It is the process of obtaining the highest strength and elastic intersection of iron-containing or iron-based metal products by heat treatment to a limited extent.
The modern tempering process may in theory be similar to the ancient process, but the equipment used today has been greatly improved. For example, quenching, which once required a homogeneous liquid to properly precipitate hardening of ferrous alloys, can now be accomplished using vacuum or air flow techniques. The tempering furnace also has the new function of "softening" the ferrous metal after the product has been quenched.
Iron-based metal products are uniformly heated to temperatures up to 1,650°F (900°C) and then immersed in a liquid bath or air oven. Typically, the material will be allowed to soak in the quenching environment for several minutes to promote the formation of high strength martensite in the material before quenching it in the liquid material. After the product has cooled, it is transferred to a tempering oven to reduce its strength and brittleness to the desired level.
Tempering furnaces use ceramic heating elements lined with wires or coils to uniformly heat the sample chamber to different heating ranges, depending on the desired material properties of the product. Iron-based metals are heated to between 300 – 750°C (572 – 1382°F) in a tempering furnace to promote phase transformation within the martensitic structure and reduce the hardness of the material while increasing its ductility. Crucially, the tempering furnace can accurately maintain temperature levels and temperature uniformity throughout the sample chamber to eliminate the possibility of metal warping or fracture.
