Basic Heat Treatment

Heat Treatment Process Terms and Definitions

What is Heat Treatment?

Definition of Heat Treatment- A process used to change the physical or chemical property of a material. Heat treatment of materials include:

metal heat treatment - titanium heat treatment - heat treatment of aluminum alloys - heat treatment of stainless steel - heat treatment of  brass - heat treatment of carbon steel - heat treatment of iron

Pacific Metallurgical, a heat treatment company in Kent, WA is a leader in industrial heat treatment services to the Pacific Northwest. 

Below are various heat treatment processes and heat treatment definitions in alphabetical order.

Alpha Case Titanium

In titanium, a hard, brittle surface layer caused by reaction of the titanium with oxygen.

Aluminum Tempering Designations

O - Full anneal

F - As fabricated

H - Strain hardened

W - Solution treating, quenching, and not aging. Material must be held cold prior to aging, typically below zero degrees F. Times and temperatures depend upon the specification the alloy is being heat treated to.

T - Heat treatment of aluminum alloys to produce a stable temper other than O. Applies to products that are thermally treated, with or without supplementary strain hardening, to produce stable tempers. The T is always followed by one or more digits.

Annealing Heat Treatment

Annealing heat treatment process is heating the material above the critical temperature, holding long enough for transformation to occur and slow cooling. Full annealing heat treatment differs from normalizing heat treatment in that the annealing temperature is typically 150-200F lower than the normalizing temperature and the cooling rate is slower. This establishes a soft microstructure and thus a soft product.

Annealing materials include:

Annealing Copper - Annealing Steel - Annealing Stainless Steel - Brass Annealing

Austenitizing Definition

Austenitizing heat treatment is heating a steel above the critical temperature, holding for a period of time long enough for transformation to occur. The material will be hardened if austenitizing is followed by quenching at a rate that is fast enough to transform the austenite into martensite.

Carburizing Steel

Carburizing heat treatment is the introduction of carbon into the surface of steel. Carburizing occurs when the steel is heated above the critical temperature in a carburizing furnace which contains more carbon than the steel contains.

Critical Temperature Definition

For steel and steel alloys, the temperature above which austenite is the stable phase.

Decarburization Definition

Decarburization is the removal of carbon from the surface of a steel. Decarburization occurs when the steel is heated above the critical temperature in an atmosphere which contains less carbon than the steel contains.

Deep Freezing Steel

Deep Freezing is cooling a steel to approximately -100F or lower in order to complete the transformation of austenite to martensite.

Gas Nitriding Heat Treatment

Gas Nitriding process is the purposeful introduction of nitrogen in the surface of a steel which results in a thin, hard case. Gas nitriding heat treatment is typically performed at 50-75F below the tempering temperature of the steel being nitride. Material must be in the quenched and tempered condition prior to nitriding for best effectiveness. Steels which contain Tungsten, Vanadium, Molybdenum, Aluminum, and/or Chromium form the hardest nitride layers.

Hot Oil Quenching Heat Treatment / Marquenching Definition

Oil Quenching heat treatment that is held at a temperature at or below the martensite start. This helps to prevent quench cracking. May also be referred to as Marquenching.

Metal Heat Treatment

Metal Heat Treatment process is the heating and/or cooling a metal in a controlled way to produce a desired condition or properties.

Normalizing Heat Treatment Definition

Normalizing Heat Treatment process is heating a steel above the critical temperature, holding for a period of time long enough for transformation to occur, and air cooling. Normalized heat treatment establishes a more uniform carbide size and distribution which facilitates later heat treatment operations and produces a more uniform final product.

Solution Annealing - Solution Heat Treatment Definition

Some alloys (aluminum, PH stainless steels, Ti) harden by precipitating microscopic particles during aging. Solution heat treatment / solution annealing takes these particles and puts them back into solution.  In the solution annealing process, the alloy is heated to a high temperature, held for a period of time related to the section size of the material and air cooled or faster. This traps the precipitates in solution.

Spheroidize Annealing Heat Treatment

Spheroidize Annealing is heating and cooling to produce a spheroidal or globular form of carbide in steel. Spheroidizing annealing process is typically used for high carbon alloys.

Steel Aging (also referred to as Precipitation Hardening)

Precipitation Hardening is the heating of alloys, in the solution treated condition, to a lower temperature, which allows a relatively uniform distribution of microscopic particles throughout the alloy. The aging process results in alloy strengthening.

Steel Tempering Heat Treatment

Steel Tempering process is heating steel to reduce the hardness and strength of the material and increase the ductility of the material.

Stress Relieving Heat Treatment Definition

Stress Relieving heat treatment process is heating to a temperature in order to relieve internal stresses in the material and lower the hardness of the surface of the material.

Sub Critical Annealing 

Sub-critical annealing is heating to a temperature below the critical temperature.  This process lowers the hardness of steel, but does not result in as low of hardness as a full anneal would.


PRI NADCAP website
Heat Treat Forum
Industrial Heating
Metal Treating Institute
Heat Treating News
Metaltest Inc.