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Heat Treating Steel Definitions

Heat Treating Definitions– This glossary of heat-treating terms has been adopted by the American Foundrymen’s
Association, the American Society for Metals, the American Society for Testing
and Materials, and the Society of Automotive Engineers. Since it is not intended
to be a specification but is strictly a set of definitions, temperatures have
purposely been omitted.

welder heatAging: Describes a time-temperature-dependent change in the properties of certain alloys.
Except for strain aging and age softening, it is the result of precipitation from
a solid solution of one or more compounds whose solubility decreases with decreasing
temperature. For each alloy susceptible to aging, there is a unique range of time-temperature
combinations to which it will respond.

Annealing: A term denoting a treatment, consisting of heating to and holding at a suitable
temperature followed by cooling at a suitable rate, used primarily to soften but
also to simultaneously produce desired changes in other properties or in microstructure.
The purpose of such changes may be, but is not confined to, improvement of machinability
; facilitation of cold working; improvement of mechanical or electrical properties;
or increase in stability of dimensions. The time-temperature cycles used vary
widely both in maximum temperature attained and in cooling rate employed, depending
on the composition of the material, its condition, and the results desired. When
applicable, the following more specific process names should be used: Black Annealing,
Blue Annealing, Box Annealing, Bright Annealing, Cycle Annealing, Flame Annealing,
Full Annealing, Graphitizing, Intermediate Annealing, Isothermal Annealing, Process
Annealing, Quench Annealing, and Spheroidizing . When the term is used without
qualification, full annealing is implied. When applied only for the relief of
stress, the process is properly called stress relieving.

Box annealing or pot annealing, used mainly for sheet, strip, or wire.

Heating hot-rolled sheet in an open furnace to a temperature within the transformation
range and then cooling in air, to soften the metal. The formation of a bluish
oxide on the surface is incidental.

Annealing in a sealed container under conditions that minimize
oxidation. In box annealing, the charge is usually heated slowly to a temperature
below the transformation range, but sometimes above or within it, and is then
cooled slowly; this process is also called “close annealing” or “pot

Annealing in a protective medium to prevent discoloration of the
bright surface.

An annealing process employing a predetermined and closely controlled
time-temperature cycle to produce specific properties or microstructure.

in which the heat is applied directly by a flame.

Austenitizing and then cooling at a rate such that the hardness of the product
approaches a minimum.

Graphitizing: Annealing in such a way that some or all of the carbon is precipitated as graphite.

Annealing at one or more stages during manufacture and before final thermal treatment.

Austenitizing and then cooling to and holding at a temperature at which austenite
transforms to a relatively soft ferrite-carbide aggregate.

An imprecise term used to denote various treatments that improve workability.
For the term to be meaningful, the condition of the material and the time-temperature
cycle used must be stated.

Annealing an austenitic alloy by Solution Heat Treatment.

and cooling in a cycle designed to produce a spheroidal or globular form of carbide.

Austempering: Quenching from a temperature above the transformation range, in a medium having
a rate of heat abstraction high enough to prevent the formation of high-temperature
transformation products, and then holding the alloy, until transformation is complete,
at a temperature below that of pearlite formation and above that of martensite

Austenitizing: Forming austenite by heating into the transformation range (partial austenitizing
) or above the transformation range (complete austenitizing ). When used without
qualification, the term implies complete austenitizing .

Baking: Heating to a low temperature in order to remove entrained gases.

Bluing: 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. This term is also used to denote a heat
treatment of springs after fabrication, to reduce the internal stress created
by coiling and forming.

A measure of the ability of an environment containing active carbon to alter or
maintain, under prescribed conditions, the carbon content of the steel exposed
to it. In any particular environment, the carbon level attained will depend on
such factors as temperature, time, and steel composition.

Replacing the carbon lost in the surface layer from previous processing by carburizing
this layer to substantially the original carbon level.

Carbonitriding: A case-hardening process in which a suitable ferrous material is heated above
the lower transformation temperature in a gaseous atmosphere of such composition
as to cause simultaneous absorption of carbon and nitrogen by the surface and,
by diffusion, create a concentration gradient. The process is completed by cooling
at a rate that produces the desired properties in the workpiece .

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 that may be a solid, liquid, or gas. Carburizing is frequently followed
by quenching to produce a hardened case.


  1. The surface layer of an iron-base alloy that 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

Cementation: The process of introducing elements into the outer layer of metal objects by means
of high-temperature diffusion.

Exposing to suitable subzero temperatures for the purpose of obtaining desired
conditions or properties, such as dimensional or microstructural stability. When
the treatment involves the transformation of retained austenite, it is usually
followed by a tempering treatment.

Heat Treatment:
A preliminary heat treatment used to prepare a material for a desired reaction
to a subsequent heat treatment. For the term to be meaningful, the treatment used
must be specified.

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.


  1. The interior portion of an iron-base alloy that after case hardening is substantially
    softer than the surface layer or case
  2. The term core is also used to designate the relatively soft central portion of
    certain hardened tool steels

Range or Critical Temperature Range : Synonymous with Transformation Range ,which
is preferred.

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 that reacts with the carbon.

Drawing: Drawing, or drawing the temper, is synonymous with Tempering, which is preferable.

alloy composition that freezes at constant temperature similar to a pure metal.
The lowest melting (or freezing) combination of two or more metals. The alloy
structure (homogeneous) of two or more solid phases formed from the liquid eutectically

Hardenability: In a ferrous alloy, the property that determines the depth and distribution of
hardness induced by quenching.

Hardening:Any process of increasing hardness of metal by suitable treatment, usually involving
heating and cooling. Also: See Aging

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
case-hardening processes are Carburizing, Cyaniding, Carbonitriding , and Nitriding

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.

A process of hardening an alloy in which a constituent precipitates from a supersaturated
solid solution. See also Aging.

An increase in hardness following the normal softening that occurs during the
tempering of certain alloy steels.

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.


A process of local heating by electrical induction.

A combination of heating and cooling operations applied to a metal
or alloy in the solid state to obtain desired conditions or properties. Heating
for the sole purpose of hot working is excluded from the meaning of this definition.

Treatment, Solution:
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 desired constituent to
enter into solid solution, followed by rapid cooling to hold the constituent in
solution. The material is then in a supersaturated, unstable state, and may subsequently
exhibit Age Hardening.

A high-temperature
heat-treatment process intended to eliminate or to decrease chemical segregation
by diffusion.

change in phase at constant temperature.

Malleablizing: A process of annealing white cast iron in which the combined carbon is wholly
or in part transformed to graphitic or free carbon and, in some cases, part of
the carbon is removed completely. See Temper Carbon.

Maraging: A precipitation hardening treatment applied to a special group of iron-base alloys
to precipitate one or more intermetallic compounds in a matrix of essentially
carbon-free martensite .

Martempering: A hardening procedure in which an austenitized ferrous workpiece is quenched into
an appropriate medium whose temperature is maintained substantially at the Ms
of the workpiece , held in the medium until its temperature is uniform throughout
but not long enough to permit bainite to form, and then cooled in air. The treatment
is followed by tempering.

Nitriding: A process of case hardening in which an iron-base alloy of special composition
is heated in an atmosphere of ammonia or in contact with nitrogenous material.
Surface hardening is produced by the absorption of nitrogen without quenching.

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.

A metal
is said to have been overheated if, after exposure to an unduly high temperature,
it develops an undesirably 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.

Patenting:A process of heat treatment applied to medium- or high-carbon steel in wire making
prior to the wire drawing or between drafts. It consists in 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

Preheating:Heating to an appropriate temperature immediately prior to austenitizing when
hardening high- hardenability constructional steels, many of the tool steels,
and heavy sections.

Rapid cooling.
When applicable, the following more specific terms should be used: Direct Quenching,
Fog Quenching, Hot Quenching, Interrupted Quenching, Selective Quenching, Slack
Quenching, Spray Quenching, and Time Quenching.

Quenching carburized parts directly from the carburizing operation.

Quenching in a mist.

imprecise term used to cover a variety of quenching procedures in which a quenching
medium is maintained at a prescribed temperature above 160 degrees F (71 degrees

A quenching procedure in which the workpiece is removed from the first quench
at a temperature substantially higher than that of the quenchant and is then subjected
to a second quenching system having a different cooling rate than the first.

Quenching only certain portions of a workpiece .

incomplete hardening of steel due to quenching from the austenitizing temperature
at a rate slower than the critical cooling rate for the particular steel, resulting
in the formation of one or more transformation products in addition to martensite

in a spray of liquid.

Interrupted quenching in which the duration of holding in the quenching medium
is controlled.

Soaking:Prolonged heating of a metal at a selected temperature.

A treatment applied to stabilize the dimensions of a workpiece or the structure
of a material such as

  1. before finishing to final dimensions, heating a workpiece to or somewhat beyond
    its operating temperature and then cooling to room temperature a sufficient number
    of times to ensure stability of dimensions in service
  2. transforming retained austenite in those materials that retain substantial amounts
    when quench hardened (see cold treatment)
  3. heating a solution-treated austenitic stainless steel that contains controlled
    amounts of titanium or niobium plus tantalum to a temperature below the solution
    heat-treating temperature to cause precipitation of finely divided, uniformly
    distributed carbides of those elements, thereby substantially reducing the amount
    of carbon available for the formation of chromium carbides in the grain boundaries
    on subsequent exposure to temperatures in the sensitizing range.

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.
This treatment may be applied to relieve stresses induced by casting, quenching,
normalizing, machining, cold working, or welding.

The free or graphitic carbon that comes out of solution usually in the form of
rounded nodules in the structure during Graphitizing or Malleablizing .

Tempering: Heating a quench-hardened or normalized ferrous alloy to a temperature below the
transformation range to produce desired changes in properties.

A treatment in which quench hardened steel is given two complete tempering cycles
at substantially the same temperature for the purpose of ensuring completion of
the tempering reaction and promoting stability of the resulting microstructure.

A precautionary interim stress-relieving treatment applied to high
hardenability steels immediately after quenching to prevent cracking because of
delay in tempering them at the prescribed higher temperature.

Brittleness :
Brittleness that results when certain steels are held within, or are cooled slowly
through, a certain range of temperatures below the transformation range. The brittleness
is revealed by notched-bar impact tests at or below room temperature.

Ranges or Transformation Temperature Ranges:
ranges of temperature within which austenite forms during heating and transforms
during cooling. The two ranges are distinct, sometimes overlapping but never coinciding.
The limiting temperatures of the ranges depend on the composition of the alloy
and on the rate of change of temperature, particularly during cooling.

The temperature at which a change in phase occurs. The term is
sometimes used to denote the limiting temperature of a transformation range. The
following symbols are used for iron and steels:

=In hypereutectoid steel, the temperature at which the solution of cementite in
austenite is completed during heating

= The temperature at which austenite begins to form during heating

= The temperature at which transformation of ferrite to austenite is completed
during heating

= The temperature at which austenite transforms to delta ferrite during heating

Ae3, Aecm , Ae4 = The temperatures of phase changes at equilibrium

=In hypereutectoid steel, the temperature at which precipitation of cementite
starts during cooling

= The temperature at which transformation of austenite to ferrite or to ferrite
plus cementite is completed during cooling

= The temperature at which austenite begins to transform to ferrite during cooling

= The temperature at which delta ferrite transforms to austenite during cooling

= The temperature at which transformation of austenite to martensite starts during

= The temperature, during cooling, at which transformation of austenite to martensite
is substantially completed