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Acicular Ferrite
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A highly substructed nonequaixed ferrite formed upon continuous cooling by a mixed diffusion and shear mode of transformation that begins at a temperature slightly higher than the transformation temperature range for upper bainite in that it has a limited amount of carbon available; thus, there is only a small amount of carbide present.
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Acid Embrittlement
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A form of hydrogen embrittlement that may be induced in some metals by acid treatment.
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Acid Steel
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Steel produced in a furnace with an acid lining, i.e. consisting of
a siliceous refractory and under a siliceous slag. With an acid
slag, carbon, silicon and manganese only are removed so that the pig
iron must not contain sulfur and phosphorus in percentages
exceeding those permissible for the specification being made. Most
steel manufactured today is in furnaces with basic linings. |
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Age Hardening
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Hardening by aging, usually after rapid cooling or cold working. |
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Age Softening
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Spontaneous decrease of strength and hardness that takes place at
room temperature in certain strain-hardened alloys, especially those
of aluminum. |
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Aging
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Aging is a structural change, usually by precipitation, that occurs
in some alloys after a preliminary heat treatment or cold working
operation. Aging may take place in some alloys at room temperature
in moderate time (days) or in others may be done in shorter time at
furnace temperatures. Over-aging may be done at a temperature above
normal to produce some desirable modification of physical
properties. |
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Air-Hardening Steel
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An alloy steel which will form martensite and develop a high
hardness when cooled in air from its proper hardening temperature.
Sometimes referred to as self- hardening steel. A steel that becomes
fully hardened when cooled in air from above its critical point and
does not require rapid quenching by oil or water. The risk of
distortion is greatly reduced by air hardening. High Speed Steel was
one of the earliest examples of this type of steel. |
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Allotropy
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The property possessed by certain elements to exist in two or more
distinct forms that are chemically identical but have different
physical properties. In the case of iron the crystal structure has
one form at room temperature and another at high temperature. When
heated above 910°C the atomic structure changes from body centered
cubic to face centered cubic but reverts again when cooled. The
allotropy of iron modifies the solubility of carbon, and it is
because of this that steel can be hardened. |
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Alloy Steel
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A steel to which one or more alloying elements other than carbon
have been deliberately added (e.g. chromium, nickel, molybdenum) to
achieve a particular physical property. |
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Alpha Iron
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The body centered cubic form of iron which, in pure iron, exists up
to 910°C. |
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Aluminizing
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Forming a corrosion and oxidation-resistant coating on a metal by
coating with aluminum and usually diffusing to form an aluminum-rich
alloy. |
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Annealing
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Heating steel to, and holding at a suitable temperature, followed by
relatively slow cooling. The purpose of annealing may be to remove
stresses, to soften the steel, to improve machinability, to improve
cold working properties, to obtain a desired structure. The
annealing process usually involves allowing the steel to cool slowly
in the furnace. |
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Annealing, Finish |
A
sub-critical annealing treatment applied to cold-worked low-or
medium-carbon steel. Finish annealing, which is a compromise
treatment, lowers residual stresses, thereby minimizing the risk of
distortion in machining while retaining most of the benefits to
machinability contributed by cold working. |
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Annealing, Intermediate |
Annealing wrought metals at one or more stages during manufacture
and before final treatment. |
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Annealing, Partial |
An imprecise term used to
denote a treatment given to cold-worked material to reduce their
strength to a controlled level or to affect stress relief. To be
meaningful, the type of material, the degree of cold work, and the
time-temperature schedule must be stated. |
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Anneal to Temper
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A final partial anneal that softens a cold worked nonferrous alloy
to a specified level of hardness or tensile strength. |
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Arc Furnace
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A steel melting furnace in which heat is generated by an arc between
graphite electrodes and the metal. Both carbon and alloy steels are
produced in electric arc furnaces and scrap rather than molten metal
is used as the base material. Furnaces with capacities up to 200
tons are now in use. |
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Atmosphere
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The gaseous environment in which the metal being treated is heated
for processing. Atmospheres are used to protect from chemical change
or to alter the surface chemistry of steel through the addition or
removal of carbon, nitrogen, hydrogen, and oxygen and to add certain
metallic elements as chromium, silicon, sulfur, etc. |
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Austempering
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Quenching from a temperature above the transformation range to a
temperature above the upper limit of martensite formation, and
holding at this temperature until the austenite is completely
transformed to the desired intermediate structure, for the purpose
of conferring certain mechanical properties. |
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Austenite
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This is the name for any solid solution in
which gamma iron is the solvent. It
is a phase in steel where it consists of face-centered cubic iron
with carbon in solid solution. It is non-magnetic and unstable at
room temperature. Austenite is a structure name and means
nothing as to composition. It is the structure from which all
quenching heat treatments must start. |
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Austenitic Grain Size
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The size attained by the grains of steel when heated to the
austenitic region; may be revealed by appropriate etching of cross
sections after cooling to room temperature. |
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Austenitic Steels
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Steels containing high percentages of certain alloying elements such
as manganese and nickel which are austenitic at room temperature and
cannot be hardened by normal heat-treatment but do work harden. They
are also non-magnetic. Typical examples of austenitic steels include
the 18/8 stainless steels and 14% manganese steel. |
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Austenitizing
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Forming austenite by heating a ferrous alloy into the transformation
range (partial austenitizing) or above the transformation range
(complete austenitizing). When used without qualification, the term
implies complete austenitizing. |
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Austenitizing Temperature
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The temperature at which a steel is substantially all austenite. |
