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QUICK FACT GUIDES FOR MACHINISTS
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GUIDES
FUNDAMENTALS OF
DRILLING & TAPPING
FUNDAMENTALS
OF THREADING ON A LATHE
FUNDAMENTALS OF
WORKING BETWEEN CENTERS
FUNDAMENTALS
OF MILLING
FUNDAMENTALS
OF SAWING
METALWORKING
SHOP TERMS
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HEAT TREATMENT TERMS: AGING:
A change in a metal by which its structure recovers from an unstable condition
produced by quenching or by cold working, The change in structure consists in
precipitation, often submicroscopic, and is marked by a change in physical
properties. Aging which takes place slowly at room temperature may be
accelerated by a slight increase in temperature. See also Stress Relieving.
AIR
HARDENING:
See Hardening, Air. ANNEALING:
A
process involving heating and cooling applied usually to induce softening. The
term is also used to cover treatments intended to remove stresses, alter
mechanical or physical properties, produce a definite microstructure, remove
gases. Certain specific heat treatment of iron-base alloy covered by the term
annealing are: Black Annealing, Box Annealing, Bright Annealing, Full
Annealing, Graphitizing, Malleablizing, Process Annealing. ANNEALING,
BLACK:
A process of box annealing iron-base alloy sheets after hot rolling, shearing
and pickling. The process does not impart a black color to the product if
properly done. The name originated in the appearance of the hot-rolled material
before pickling and annealing. ANNEALING,
BLUE:
A process of softening iron-base alloys in the form of hot-rolled sheet, in
which the sheet is heated in the open furnace to a temperature within the
transformation range and cooled in air, the formation of a bluish oxide on the
surface is incidental. ANNEALING,
BOX: A
process of annealing which, to prevent oxidation, is carried out in a suitable
closed metal container with or without packing material. The charge is usually
heated slowly to a temperature below, but sometimes above or within the
transformation temperature range and cooled slowly. It is also called Close
Annealing or Pot Annealing. ANNEALING,
CLOSE: See
Annealing, Box. ANNEALING,
FLAME:
A process in which the surface of an iron-base alloy is softened by localized
heat applied by a high temperature flame. ANNEALING,
FULL:
A softening process in which an iron-base alloy is heated to a temperature above
the transformation range and, after being held for a proper time at this
temperature, is cooled slowly to a temperature, below the transformation range.
The objects are ordinarily allowed to cool slowly in the furnace, although they
may be removed from the furnace and cooled in some medium which assures a slow
rate of cooling. ANNEALING,
POT:
See Annealing, Box. ANNEALING,
PROCESS: A
process commonly applied in the sheet and wire industries, in which an iron-base
alloy is heated to a temperature close to, but below, the lower limit of
transformation range and subsequently cooled. This process is applied for the
purpose of softening for further cold working. AUSTEMPERING:
A trade name for a patented heat treating process consisting in quenching an
iron-base alloy from a temperature above the transformation range in a medium
having a suitably high rate of heat abstraction, and maintaining the alloy,
until transformation is complete, at a temperature which is below that of
pearlite formation and above that of martensite formation. The temperature for
austenite transformation is chosen on the
basis of the properties desired. BLUEING:
A treatment of the surface of iron-base alloys, usually in the form of sheet or
strip, on which, by the action of air or steam at a suitable temperature, a thin
blue oxide film is formed on the initially scale-free surface, as a means of
improving appearance and resistance to corrosion. The term is also used to
denote a heat treatment of springs after fabrication, to reduce the internal
stress created by coiling and forming. BRUNORIZING:
A trade name for a special treatment applied to steel rails which, after cooling
to a temperature below the transformation range, are reheated to a temperature
slightly above the range, and then are allowed to cool in the air, the ends of
rails being partially quenched by jets of compressed air. BURNT:
A
term applied to a metal permanently damaged by being heated to a temperature
close to the melting point. The damage may involve melting of some constituent
or penetration by, and reaction of the metal with, a gas such as oxygen, or by
segregation of component elements of the metal. CARBURIZING:
A
process in which carbon is introduced into a solid iron-base alloy by heating
above the transformation temperature range while in contact with a carbonaceous
material which may be solid, liquid or gas. Carburizing is frequently followed
by quenching to produce a hardened case. The carbonizing is sometimes used
erroneously in place carburizing. CASE:
(1) The surface layer of an iron-base alloy which has been suitably altered in
composition and can be made substantially harder than the interior or core by a
process of case hardening. (2) The term case is also used to designate the
hardened surface layer of a piece of steel that is large enough to have a
distinctly softer core or center. CASE
HARDENING:
See Hardening, Case. CEMENTATION:
The
process of introducing elements into the outer layer of metal objects by means
of high temperature diffusion. CONTROLLED
COOLING:
A term used to describe a process by which a steel object is cooled from an
elevated temperature, usually from the final hot forming operation in a
predetermined manner of cooling to avoid hardening, cracking, or internal
damage. CORE:
(1) The interior portion of
an iron-base alloy which after case hardening is substantially softer than the
surface layer or case. (2) The term core is also used to designate the relative
soft central portion of certain hardened tool steels. See also Case. CRITICAL
RANGE OR CRITICAL TEMPERATURE RANGE: Synonymous with Transformation Range, which is the preferred
term. CYANIDE
HARDENING: See
Hardening, Cyanide. CYANIDING:
A
process of case hardening an iron-base alloy by the simultaneous absorption of
carbon and nitrogen by heating in a cyanide salt. Cyaniding is usually followed
by quenching to produce a hard case. DECARBURIZATION:
The loss of carbon from the surface of an iron-base alloy as the result of
heating in a medium which reacts with the carbon. DRAWING:
Steel is "drawn" or tempered by reheating after hardening to some
temperature below the critical temperature range and then cooling the steel.
This heat treatment is often referred to as drawing, but the term tempering is
preferable. DRAWING
BACK:
Reheating after hardening to a temperature below the critical range for the
purpose of improving the ductility and or lowering the hardness of the steel. FLAME
HARDENING: See
Hardening, Flame. GRAPHITIZING:
An
annealing process applied to certain iron-base alloys, such as cast iron some
steels with high carbon and silicon contents, by which the combined carbon is
wholly or in part transformed to graphite or free carbon. See Temper Carbon.
HARDENING:
Any
process of increasing hardness of metal by suitable treatment, usually involving
heating and cooling. HARDENING,
AIR (AIR QUENCHING): A
hardening process wherein the steel is heated to the hardening temperature and
cooled in air. Unless the steel is high in carbon, or an alloy, or both, it will
not show much increase in hardness when air hardened. HARDENING,
AGE: See
Aging. HARDENING,
CASE:
A process of surface hardening involving a change in the composition of the
outer layer of an iron-base alloy followed by appropriate thermal treatment.
Typical casehardening process are Carburizing, Cyaniding, Carbo Nitriding and
Nitriding.
In order to harden low-carbon steel it
is necessary to increase the carbon content of the surface of the steel so that
a thin outer "case" can be hardened by heating the steel to the
hardening temperature and then quenching it.
The process therefor, involves two
separate operations. The first is the carburizing operation for impregnating the
outer surface with sufficient carbon, and then the second operation is that of
heat-treating the carburized parts so as to obtain a hard outer case and, at the
same time, give the "core" the required physical properties. The term
"casehardening" is ordinarily used to indicate the complete process of
carburizing and hardening. HARDENING,
CYANIDE: This
process is employed to produce what is known as superficial hardness. This
superficial hardening is the result of carburizing a very thin outer skin (which
may only be a few thousandths of an inch thick) by immersing the steel in a bath
containing sodium cyanide. HARDENING,
FLAME:
A process of heating the surface layer of an iron-base alloy above the
transformation temperature range by means of a high temperature flame, followed
by quenching.
This method of hardening is especially
applicable to the selective hardening of large steel forging or castings which
must be finished-machined prior to heat-treatment, or which because of size or
shape cannot be heat-treated by using a furnace or bath. HARDENING,
INDUCTION:
A surface hardening process consisting of heating ferrous metals by
electro-magnetic induction, followed by immediate quenching. HARDENING,
PACK:
The purpose of this process is to protect the work, prevent scale formation,
insure uniform heating, and minimize the danger of cracking or warpage. The work
is packed, as in carburizing, and the same type of receptacle is used. HARDENING,
PRECIPATION: A
process of hardening an alloy in which a constituent precipitates from a
supersaturated solid solution. See Also Aging. HARDENING,
SECONDARY:
An increase in hardness following the normal softening that occurs during
tempering of certain alloy steels. HARDENING,
SUPERFICIAL: When
low carbon steel is subjected to the cyanide hardening process, a very thin but
extremely hard surface is obtained, and this is known as superficial hardening.
This hard outer skin may be only a few thousandths of an inch thick, and that is
the important difference between superficial hardening and ordinary
casehardening. See also Hardening, Cyanide. HEATING,
DIFFERENTIAL: A
heating process by which the temperature is made to vary throughout the object
being heated so that on cooling different portions may have such different
physical properties as may be desired. HEATING,
INDUCTION:
A process of local heating by electrical induction. HEAT
TREATMENT, SOLUTION: A
treatment in which an alloy is heated to a suitable temperature and held at this
temperature for a sufficient length of time to allow a constituent in solution.
The material is then in a supersaturated, unstable state, and may subsequently
exhibit Age Hardening. HOMOGENIZING:
A
high temperature heat-treatment process intended to eliminate or to decrease
chemical segregation by diffusion. INDUCTION
HARDENING: See
Hardening, Induction. MALLEABLIZING:
A process of annealing white cast iron in which the combined carbon is wholly or
in part transformed to graphite or free carbon, and, in some case, part of the
carbon is removed completely. See Temper Carbon. NITRIDING:
A
process of case hardening in which an iron-base alloy by the simultaneous
absorption carbon and nitrogen by heating in an atmosphere of ammonia or in
contact with nitrogenous material. Surface hardening is produced by the
absorption of nitrogen without quenching. NITRIDING,
CARBO:
A process of case hardening an iron-base alloy by the simultaneous absorption of
carbon and nitrogen by heating in a gaseous atmosphere of suitable composition,
followed by either quenching or cooling slowly as required. NORMALIZING:
A process in which an iron-base alloy is heated to a temperature above the
transformation range and subsequently cooled in still air at room temperature.
Normalizing is intended to put the
steel into a uniform unstressed condition of proper grain size and refinement so
that it will properly respond to further heat-treatment. OVERHEATED:
A metal is said to have been overheated if, after exposure to an unduly high
temperature, it develops an undesirable coarse grain structure but is not
permanently damaged. The structure damaged by overheating can be corrected by
suitable heat treatment or by mechanical work or by a combination of the two. In
this respect it differs from a Burnt structure. PACK
HARDENING:
See Hardening, Pack. PATENTING:
A process of heat treatment applied to medium or high carbon steel in wire
making prior to the drawing or between draws. It consists of heating to a
temperature above the transformation range, followed by cooling to a temperature
below that range in air or in a bath of molten lead or salt maintained at a
temperature appropriate to the carbon content of the steel and the properties
required of the finished product. PREHEATING:
(1) A general term used to describe a heating applied preliminary to some
further thermal or mechanical treatment.
(2) A term specifically applied to
tool steel to describe a process in which the steel is heated slowly and
uniformly to a temperature below the hardening temperature and is then
transferred to a furnace in which the temperature is substantially above the
preheating temperature. QUENCHING:
A process of rapid cooling from an elevated temperature, by contact with
liquids, gases or solids. QUENCHING,
DIFFERENTIAL:
A quenching process by which only certain desired portions of the object are
quenched and hardened. QUENCHING,
HOT: A
process of quenching iron-base alloys in a medium, the temperature of which is
substantially higher than atmospheric temperature. QUENCHING,
POT: A
process of quenching carburized parts directly from the carbonizing box or pot. SANDBERG
SORBITIC TREATMENT:
A treatment in which carbon steel objects are moderately hardened, either wholly
or in part. It consists of cooling the parts to be hardened through the
transformation range at a moderately rapid rate by the application of jets of
air, steam, or atomized water and then allowing the residual heat in the object
to effect a tempering operation. SOAKING:
Prolonged heating of a metal at a selected temperature. SPHEROIDIZING:
Any process of heating and cooling steel that produces a rounded or globular
form of carbide in the structure. STRESS
RELIEVING: A
process to reduce internal residual stresses in a metal object by heating the
object to a suitable temperature and holding for a proper time at that
temperature. The treatment may be applied to relieve stresses induced by
casting, quenching, normalizing, machining, cold working or welding. Stress
relieving is sometimes termed Aging. SUPERFICIAL
HARDENING: See
Hardening, Superficial. TEMPER
CARBON:
The free or graphitic carbon which comes out of solution usually in the form of
rounded nodules in the structure during Graphitizing or Malleablizing.
TEMPERING:
A process of reheating hardened or normalized steel to a temperature
below the transformation temperature range, followed by any desired rate of
cooling. TRANSFORMATION
RANGE:
In ferrous alloys the transformation range on heating is the temperature
interval within which austenite forms. The transformation range on cooling is
the temperature interval in which austenite disappears. Distinction must be made
between the two ranges. They may overlap but never coincide. The limiting
temperatures of the ranges depends on the composition of the alloy and,
particularly for the cooling, on the rate of change of temperature. |
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Copyright © 2002 QUICK FACT GUIDES FOR MACHINISTS
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