Heat Treating

Some of the most common Heat Treatments are listed below:

Hardening
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 blades)

Annealing
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
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
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 process

Carburizing
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.

Austentizing
The term is derived from the grain structure formed by quenching from the Austentizing temperature (also see hardening.

Nitriding
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.

Other

Vapor Deposition