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Aging: the process of holding metals at room
temperature or at a predetermined temperature for the purpose
of increasing their hardness and strength by precipitation;
aging is also used to increase dimensional stability in metals
such as castings.
AISI: Abbreviation for American Iron &
Steel Institute.
Allotropy: The ability of a material to exist
in several crystalline forms.
Alloy: A substance that has metallic properties
and is composed of two or more chemical elements of which at
least one is a metal.
Anneal: To heat then cool (as steel), usually
for softening and making the metal less brittle; it also refers
to treatments intended to alter the mechanical or physical properties
to produce a definite microstructure.
ASTM: Abbreviation for American Society for Testing
Materials.
Austenite: A solid solution of iron and carbon
and sometimes other elements in which gamma iron characterized
by a face-centered cubic crystal structure is the solvent.
Austenitizing: The process of forming austenite
by heating a ferrous alloy above the transformation range.
AWS: Abbreviation for American Welding Society.
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Brittleness:
The property of materials that will not deform under load but
tend to break suddenly;for example, cast iron and glass are
brittle. Brittleness is the property opposite to plasticity.
Bright Annealing/Bright Hardening: Annealing in a protective
medium to prevent discoloration of the bright surface.
Carburizing: A process that introduces carbon
into a heated solid ferrous alloy by having it in contact with
a carbonaceous material. The metal is held at a temperature
above the transformation range for a period of time. This is
generally followed by quenching to produce a hardened case.
Case Hardening: A process in which a ferrous alloy
is hardened so that the surface layer or case is made considerably
harder than the interior or core. Some case-hardening processes
are carburizing and quenching, cyaniding, carbonitriding, nitriding,
flame hardening, and induction hardening.
Cast Iron: Iron containing 2 or 4 1/2 percent
carbon, silicon, and other trace elements. It is used for casting
objects into molds. Cast iron is somewhat brittle.
Cementite: Also known as iron carbide, a compound
of iron and carbon (Fe3C).
Critical Temperature: The preferred term used by metallurgists
is transformation temperature. The lower A1 and the upper A3
temperatures are the boundaries of the transformation range
in which ferrite transformations into austenite.
Cryogenic Treatment: Same as cold treatment
and deep freezing. Exposing steel to suitable subzero temperatures
(-85 C, or -120 F) for the purpose of obtaining desired conditions
or properties such as dimensional or micro- structural stability.
Decarburization: The loss of carbon from the
surface of a ferrous alloy as a result of heating it in the
presenceof a medium such as oxygen that reacts with the carbon.
Degrease: To remove oil and grease from adhered
surfaces.
Diffusion: The process of inter-mingling atoms
or other particles within a solution. In solids, it is a slow
movement of atoms for areas of high concentration toward areas
of low concentration. The process may be (a) migration of interstitial
atoms such as carbon, (b) movement of vacancies, or (c) direct
exchange of atoms to neighboring sites.
Drawing: A term sometimes used for the process
of tempering hardened steel. Also used for metal forming in
presses and forming wire.
Ductility: The property of a material to deform permanently,
or to exhibit plasticity without rupture, while under tension.
Elasticity: The ability of a material to return
to its original form after a load has been removed.
Equilibrium: A condition of balance in which
all the forces or processes that are present are counterbalanced
by equal or opposite forces or processes where the condition
appears to be one of rest rather than of change.
Ferrite: A magnetic form of iron. A solid solution
in which alpha iron is the solvent, characterized by a body-centered
cubic crystal structure.
Forging: The shaping of metal by hammering
or pressing. Although forging may be used to shape malleable
metals in the cold state, the application of heat increases
plasticity and permits greater deformation without inducing
undue strain in the metal.
Fracture: A ruptured surface of metal that
shows a typical crystalline pattern. Fatigue fractures, however,
often display a smooth, clam-shell appearance.
Grain: Individual crystals in metals.
Hardenability: The property that determines
the depth and distribution of hardness in a ferrous alloy induced
by heating or quenching.
Hardening: Increasing hardness of metals by
suitable treatment, usually involving heating and cooling. More
specific terms include age hardening, case hardening, flame
hardening, induction hardening, precipitation hardening, and
quench hardening.
Hardness: The property of a metal to resist
being permanently deformed. This is divided into three categories:
The resistance to penetration, abrasion, and elastic hardness.
Homogeneous Carburizing: Use of carburizing
process to convert low-carbon ferrous to allow one of uniform
and higher carbon content throughout the section.
Inclusions: Particles of impurities that are usually
formed during solidification and are usually in the form of
silicates, sulfides, and oxides.
Induction Hardening: A surface hardening process in
which only the surface layer of a suitable ferrous work piece
is heated by electromagnetic induction to above the upper critical
temperature and immediately quenched.
Macroscopic: Structural details on an object
that are large enough to be observed by the naked eye or with
low magnification (about 10x).
Macrostructure: The structure of metals as revealed by macroscopic
examination.
Magnetic annealing: Magneto-electronics, the
science underlying a new generation of semiconductor technology.
Devices that rely on an electron's spin to perform their functions
form the foundation of spintronics - short for spin based electronics
and also know as magneto-electronics.
Martensite: An unstable constituent that is
formed by heating and quenching steel. It is formed without
diffusion and only below a certain temperature, known as the
Ms temperature. Martensite is the hardest of the transformation
products of austenite, having an acicular, or needlelike, microstructure.
Metallurgy: The science and study of the behaviors
and properties of metals and their extraction from their ores.
Microscopy: The use of, or investigation with
, the microscope.
Microstructure: The structure of polished and etched metal specimens,
as seen enlarged through a microscope.
Neutral Hardening: To harden carbon steel parts
by heating them to the proper temperature in atmospheres such
as pure nitrogen, nitrogen and natural gas, or nitrogen-methanol,
followed by quenching.
Nitriding: Introducing nitrogen into the surface layer
of a solid ferrous alloy by holding at a suitable temperature
(below Ac1 for ferritic steels) in contact with a nitrogenous
material, usually ammonia or molten cyanide of appropriate composition.
Quenching is not required to produce a hard case.
Nitrocarburizing: Any of several processes in which
both nitrogen and carbon are absorbed into the surface layers
of a ferrous material at temperatures below the lower critical
temperature and, by diffusion, create a concentration gradient.
Nitrocarburizing is performed primarily
to provide an antiscuffing surface layer and to improve fatigue
resistance. Compare with carbonitriding.
Nonferrous: Metals other than iron or iron
alloys.
Normalizing: Heating a ferrous alloy to a suitable temperature
above the transformation range and then cooling in below the
transformation range.
Oxidation: The slow or rapid reaction of oxygen
with other elements; burning. In metals, the overoxidation during
heating under oxidizing conditions often results in permanent
damage to metals.
Oxynitriding: Properties of a black oxide treatment
at the end of a nitride cycle for corrosion resistance.
Precipitation Hardening: A process of hardening
an alloy by heat treatment, in which a constituent precipitates
from a supersaturated solid solution while at room temperature
or at some slightly elevated temperature.
Quenching: The process of rapid cooling of
metal alloys for the purpose of hardening. Quenching media include
air, oil, water, molten metals, and fused salts.
SAE: Abbreviation for The Society of Automotive
Engineers.
Scale: The surface oxidation on metals that
is caused by heating in air or in other oxidizing atmospheres.
Soaking: A prolonged heating of metal at a
predetermined temperature to create a uniform temperature throughout
its mass.
Solubility: The degree to which one substance
will dissolve in another.
Solution Heat Treatment: Heating an alloy to
a suitable temperature, holding at that temperature long enough
to cause one or more constituents to enter into solid solution,
and then cooling rapidly enough to hold these constituents in
solution.
Spheroidizing: A process in which carbon steel
is held for a period of time at just under the transformation
temperature. An aggregate of globular carbide is formed from
other microstructures such as pearlite.
Stainless steel: An alloy of iron containing
at least 11 percent chromium and sometimes nickel that resists
almost all forms of rusting and corrosion.
Steel: An alloy of iron and less than 2 percent
carbon plus some impurities and small amounts of alloying elements
is known as plain carbon steel. Alloy steels contain substantial
amounts of alloying elements such as chromium or nickel besides
carbon.
Strain: The unit deformation of a metal when
stress is applied.
Strength: The ability of a metal to resist
external forces. This is called tensile, compressive, or shear
strength; depending on the load. See stress.
Stress: The load per unit of area on a stress-strain
diagram. Tensile stress refers to an object loaded in tension,
denoting the longitudinal force that causes the fibers of a
material to elongate. Compressive stress refers to a member
loaded in compression, which either gives rise to a given reduction
in volume or a transverse displacement of material. Shear stress
refers to a force that lies in a parallel plane. The force tends
to cause the plane of the area involved to slide on the adjacent
planes. Torsional stress is a shearing stress that occurs at
any point in a body as the result of an applied torque or torsional
load.
Stress Relief Anneal: The reduction of residual stress
in a metal part by heating it to a given temperature and holding
it there for a suitable length of time. This treatment is used
to relieve stresses caused by welding, cold working, machining,
casting, and quenching.
Stress-Relief Heat Treatment: Uniform heating of a structure
or portion thereof to a sufficient temperature to relieve the
major portion of the residual stresses, followed by uniform
cooling.
Tempering: In ferrous metals, the stress relief of steels hardened
by quenching for the purpose of toughening them and reducing
their brittleness. In nonferrous metals, temper is a condition
produced by mechanical treatment such as cold working. An alloy
may be cold worked to the hard temper, fully softened to the
annealed temper, or two intermediate tempers.
Thermal Expansion: The increase of the dimension
of a material that results from the increased movement of atoms
caused by increased temperature.
Thermal Stress: Shear stress that is induced in a material
due to unequal heating or cooling rates. The difference of expansion
and contraction between the interior and exterior surfaces of
a metal that is being heated or cooled is an example.
Tool Steel: A special group of steels that
are designed for specific uses such as heat-resistant steels
that can be heat treated to produce certain properties, mainly
hardness and wear resistance.
Toughness: Generally measured in terms of notch toughness, which
is the ability of a metal to resist rupture from impact loading
when a notch is present. A standard test specimen containing
a prepared notch is inserted into the vise of a testing machine.
This devise, called the Izod-Charpy testing machine, consists
of a weight on a swinging arm. The arm or pendulum is released,
strikes the specimen, and continues to swing forward. The amount
of energy absorbed by the breaking of the specimen is measured
by how far the pendulum continues to swing.
Transformation Temperature: The temperatures
at which one phase transforms into another phase; for example,
ferrite or alpha iron transforms into austenite or gamma iron.
Vacuum Annealing: Annealing carried out at
sub atmospheric pressure.
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