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ANNEAL - Heating uniformly to
a temperature, within or above some critical range, and
cooling at a controlled rate to a temperature under the
critical range. This treatment is used to produce a definite
microstructure, usually one designed for best machinability
and/or to remove stresses, induce softness, and alter
ductility toughness or other mechanical properties.
SUB-CRITICAL ANNEAL - Actually
a high temperature tempering process for steel that produces
many of the benefits of annealing but does not require cooling
at a controlled rate.
SPHEROIDIZE ANNEAL - A special
type of annealing for steel that requires an extremely long
cycle. This treatment is used to produce globular carbides and
maximum softness for best machinability or to improve cold
formability.
NORMALIZE - A special type of
annealing for steel heating uniformly to a temperature at
least 100° F above the critical range and cooling in
still air at room temperature. The treatment produces a
recrystallization and refinement of the grain structure and
gives uniformity in hardness and structure to the product.
QUENCH - Healing
uniformly to a predetermined temperature and cooling rapidly
in air or liquid medium to produce a desired crystalline
structure.
TEMPER OR DRAW -
Heating uniformly to some predetermined temperature under the
critical range, holding at that temperature a designated
period of time and cooling in air or liquid. This treatment is
used to produce one or more of the following end results: A)
to soften material for subsequent machining or cold working,
B) to improve ductility and relieve stresses resulting from
prior treatment or cold working, and C) to produce desired
mechanical properties or structure in the second step of "Quench
and Temper" treatments.
STRESS RELIEVE
TEMPER - A thermal treatment to restore elastic properties and
to minimize distortion on subsequent machining or hardening
operations. This treatment is usually applied to material that
has been subjected to thermal or mechanical forces that
induced residual stress. Ordinarily, no straightening is
performed after the stress relieve temper.
CARBURIZE - In
carburizing, a high-carbon surface layer is imparted to low-
carbon steel by heating it in contact with carbonaceous
materials. On quenching after carburizing, the high-carbon "case"
becomes very hard, while the low-carbon core remains
comparatively soft. The result is very wear-resistant exterior
combined with an interior possessing great toughness.
Particularly suitable for gears, camshafts, etc.
NITRIDE - The
nitrogen case-hardening process which is termed "nitriding"
consists of subjecting machined and preferably heat-treated
parts to the action of a nitrogenous medium, commonly ammonia
gas, under certain conditions whereby surface hardness in
imparted to the material without necessitating any further
treatment. Wear resistance, retention of hardness at elevated
temperatures, resistance to certain types of corrosion and
large compressive surface stresses that improve resistance to
fatigue, are other properties imparted to the steel by
nitriding.
NITROCARBURIZE -
A low temperature case hardening process that involves the
introduction of carbon and nitrogen into a steel to produce a
thin layer of iron carbonitrides and nitrides, the "white
layer" or compound layer, with an underlying diffusion
zone. The diffusion zone increases the fatigue properties,
especially in carbon and low alloy steels. Unlike
carbonitriding, the process is performed below the critical
temperature range and therefore is relatively distortion free.
Case depth obtained is less than .003" thick.
CARBONITRIDE - A modified form
of carburizing, consisting of introducing ammonia into the
carburizing atmosphere to add nitrogen to the carburized case
as it is produced. A carbonitrided case has better
hardenability than a carburized case, and thus allows lower
alloy grades to attain required hardness at greater depth.
SOLUTION TREATMENT - A
treatment consisting of heating to an elevated temperature and
remaining there for a sufficient period of time to dissolve
precipitates and create a solid solution. The treatment, which
is actually an anneal, is the first step in precipitation
hardening. It is also used to dissolve chromium carbide
precipitates, which are detrimental to corrosion resistance,
in austenitic stainless steels (300 series.) Quenching is
required for certain materials.
AGE - Second step in
precipitation hardening. A treatment consisting of heating to
a moderate temperature and remaining there for a sufficient
period to produce the optimal precipitate size and
distribution to give the desired mechanical properties.
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