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Heat treating is a group industrial and
metalworking processes use to after the physical and chemical properties of a
material.
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Heat treatment involves the use of heating or
chilling, normally to extreme temperatures, to achieve a desired result such as
hardening or softening of a material.
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Heat
treatment techniques include:
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Annealing
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Tempering
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Normalizing
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Aging
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Quenching
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Case hardening
Annealing:
Annealing is a rather generalized term. It
consists of heating a metal to a specific temperature and then cooling at a
rate that will produce are fined microstructure. Annealing is moth often used
to soften a metal for cold working to improve machinability, or to enhance
properties like electrical conductivity.
Full annealing requires very slow cooling rates
Aging: aging a
solutionized metal will allow the alloying elements to diffuse through the
microstructure and from intermetallic particles will nucleate and fall out of
solution and act as a reinforcing phase, thereby increasing the strength of the
alloy.
Quenching
It is a process of cooling a metal very quickly. This is mot
often doen to produce a martensite transformation. In ferrous alloys, this will
often produce aharder metal, whil non- ferrous alloys will usually become
softer than normal.
Tempering: tempering
is a process of heat treating, which is used to increase the toughness of iron
based alloys, it is also a technique used to increase the toughness of glass,
for metals, tempering is usually performed after hardening, to reduce some of
the excess hardness, and is doen by heating the metal to amuch lower
temperature then was used for hardening.
Normalizing: it is a technique used to provide uniformity in grain size and composition
throughout an alloy. The term is often used for ferrous alloys that have been
heated above the upper critical temperature and then cooled in standing air is
called normalized steel. This produces steel that is much stronger than full
annealed steel, and much tougher than tempered quenched steel.
Case hardening: Case
hardening or surface hardening is the process of hardening the surface of a
metal, often low carbon steel, by infusing elements into the materials surface,
forming a thin layer of a harder alloy. Case hardening is usually done after
the part in question has been formed into its final shape, but can also be done
to increase the hardening element content of bars to be used in a pattern
welding or similar process
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