Some of the most common Heat Treatments are listed below:
Most metals can be hardened by thermal treatment. For most steels
it will depend largely on the “hardenability” of the
material. Generally the higher the carbon content the greater the
hardenability of the steel. A very common way to harden a piece
of steel is to heat it to 1600-1700F (850-900C) and rapidly cool
the piece. Rapid cooling can be accomplished by dropping the part
into water or oil, or in the case of some metals, cooling in air
will harden the metal (for example: some tool steels, and also razor
Annealing is the softening of metal by thermal treatment. Generally
this term is misused to include tempering and stress relief. In
most cases true annealing involved heating the metals to a point
where the microstructure is reformed, changing the grain size, and
removing any work hardening or stresses.
Tempering is used after hardening to lower the hardness so the part
is not too brittle. A very hard part will be brittle. By tempering
the part after hardening, the part will become tougher and be able
to with stand shock loads better
Stress relief is a thermal treatment where built up stresses from
working the material, or stresses from other thermal treatment can
be removed or at least reduced. It is generally a low temperature
Carburizing is a treatment used to increase the carbon content on
the surface (thus improving its hardenability). It is often combined
with a rapid cooling to harden the carburized part.
The term is derived from the grain structure formed by quenching
from the Austentizing temperature (also see hardening.
Similar to the Carburizing process except Nitrogen is added to the
surface in place of Carbon. A nitrided part generally has very good
surface toughness (file hard) and has better corrosion resistance,
as well as a smoother surface. Nitriding is a slower process than
carburizing and is carried out at lower temperatures.