Specifications for heat treating processes are among the most important of those shown on an engineering drawing. Proper heat treatment is a powerful tool for developing the best possible properties that a material can possess. In general, heat treatment may be described as a combination of heating and cooling operations, timed and applied to a metal or an alloy in the solid state in a way that will produce desired properties.
Principally, heat treating is used to produce strengthening, but some heat-treating processes soften, toughen, or otherwise enhance properties.
Internally, a metal or alloy consists of one or more kinds of atoms packed together in orderly three-dimensional arrangements called crystals. The crystals, in turn, are bonded together in diverse ways which are described in terms of microstructure or grain structure. Any given structure can be altered to some extent by plastic deformation from compressive, tensile, or shear forces, but the available time-temperature treatments provide a greater variety of properties. Heat treatments are carefully by combinations of such variables as time, temperature. Rate of temperature change, and furnace atmosphere, The selection of a specific treatment must be based upon knowledge of the properties desired in the finished part.
There is available today a multitude of metals and alloys designed for various purposes, There are also many different heat treating processes. Not all the treatments can be used with each metal or alloy. In other words, the treatment selected must be one that is compatible with the specified material. Heat treating cannot be selected independently of material. One is just as important as the other. You can get helpful information from here