Heat Treating Terminology
AGING - Changes in properties of certain metals and alloys occurring at ambient or moderately elevated temperatures after hot working or a heat treatment.
ANNEALING - A term that refers to softening metals by treating with sustained heat at the required temperature, followed by cooling at a controlled rate, while at the same time, producing desired results in other properties or microstructure. Annealing generally refers to slow cooling in aluminum alloys, with the focus usually being on removing stresses; inducing softness; altering ductility, toughness, electric, magnetic or other physical and mechanical properties; changing the crystalline structure, and finally producing a definite microstructure.
BRINELL HARDNESS - A hardness number determined by applying a predetermined load to the surface of a test material by using a hardened steel ball. Diameter of the depression is measured, and hardness is calculated as the ratio of the load, to the diameter of the impression.
HARDENING - Heating and quenching of certain aluminum based alloys from above the critical temperature range to produce a superior hardness.
HARDNESS - The ability of a metal to resist penetration. The principle methods of determining hardness of aluminum are the Rockwell Rb & Rf Scale, along with the use of Electrical Conductivity testing.
HEAT TREATMENT - The heating and cooling of metals or alloys in the solid state for the purpose of obtaining certain desirable conditions or properties.
MICROHARDNESS - The hardness of a material as determined by forcing an indenter into the surface of the material under a very light load, with the indentations so light that they must be measured under a microscope.
NORMALIZING - Heating ferrous alloys to approximately 100° F above the critical temperature range, followed by cooling in air, and is used to undo previous heat treating results so as to achieve a uniform grain structure.
QUENCHING - Heating materials to the proper temperature, and holding at that temperature until the desired change in crystalline structure is achieved, followed by quenching in a water, air etc. After quenching, the materials are reheated to a predetermined temperature below the
ROCKWELL HARDNESS - A test performed on a Rockwell hardness testing machine to determine hardness.
SCLEROSCOPE OR SHORE HARDNESS - A hardness test performed on a Shore
Scleroscope Hardness Testing machine. This type of testing is used primarily for large parts that cannot be tested under Rockwell or Brinell.
SUB-CRITICAL ANNEALING - Also known as Stress Relief Annealing, this procedure is used to relieve stresses. Parts are uniformly heated to 1150° F., and either air cooled or slow cooled from based on the type of part being treated, and subsequent operations to be performed.
TEMPERING - Also know as drawing, this process involves reheating previously hardened or quenched steel to a temperature below the lower critical temperature, and followed by cooling. Tempering temperatures range from 300° to 1100° F.
WATER HARDENING - Hardening of high carbon steels, straight carbon steels, and low alloy steels by quenching in water.