is controlled heating and cooling of a solid
metal or alloy by methods designed to obtain
specific properties by changing the microstructure.
Heat Treating takes place below the melting
point of the metal and changes in microstructure
take place within the solid metal. Changes
in microstructure are due to the movement
of atoms within crystal lattices in response
to heating or cooling over a period of time.
The ability to tailor properties
by heat treating has contributed greatly
to the usefulness of metals and their alloys
in an assortment of applications such as
sheet metal for cars and aircraft.
Heat treating processes
include annealing, normalizing, tempering,
stress relieving, solution treating, age
hardening, and bright hardening. Quenching,
or cooling from a higher temperature, is
an integral part of many heat treating processes
when hardening is involved.
Regardless of the reason
for the heat treating, the basic process
is the same and has three steps.
Heat the metal to a specific
- Hold the metal at that
temperature for a specific amount of time
- Cool the metal in a specific
The following heat treatment
processes are the most commonly used: