ISO/FDIS 4885

FINAL DRAFT
International
Standard
ISO/TC 17
Ferrous materials — Heat
Secretariat: JISC
treatments — Vocabulary
Voting begins on:
Matériaux ferreux — Traitements thermiques — Vocabulaire 2026-04-29
Voting terminates on:
2026-06-24
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Reference number
FINAL DRAFT
International
Standard
ISO/TC 17
Ferrous materials — Heat
Secretariat: JISC
treatments — Vocabulary
Voting begins on:
Matériaux ferreux — Traitements thermiques — Vocabulaire
Voting terminates on:
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2026
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Published in Switzerland Reference number
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 General terms .1
3.2 Terms related to annealing and normalizing . 12
3.3 Terms related to quenching . 15
3.4 Terms related to tempering and partitioning .19
3.5 Terms related to ageing .21
3.6 Terms related to surface heat treatment . 22
3.7 Terms related to thermochemical treatment . 23
3.8 Terms related to structure .32
3.9 Terms related to defects . 38
Annex A (informative) Equivalent terms . 41
Bibliography .56
Index .57

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
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Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 17, Steel, in collaboration with the European
Committee for Standardization (CEN) Technical Committee CEN/TC 459/SC 12, General issues, in accordance
with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
This fourth edition cancels and replaces the third edition (ISO 4885:2018), which has been technically
revised.
The main changes are as follows:
— the list of terms has been restructured and classified into 9 categories: general, annealing and
normalizing, quenching, tempering and partitioning, ageing, surface heat treatment, thermochemical
treatment, structure, defects;
— 66 new terms have been added, such as “continuous austenitization diagram”, “expanded austenite”,
“partitioning”, “total thickness of surface hardening depth”, etc.;
— 9 terms have been deleted, such as “acicular structure”, “ferritic steel”, “quenching temperature”, etc.;
— 4 terms have been integrated, namely “baking/ hydrogen removal annealing”, “continuous-cooling-
transformation diagram/CCT diagram”;
— 3 terms have been divided into 6 new terms, namely “blank nitriding/ blank nitrocarburizing”,
“overheating/ oversoaking”, “sub-zero treatment/ cryogenic treatment (former deep freezing)”;
— 39 terms have been added synonyms, such as “cooling function/ cooling curve”, “blackening/ blacking”,
“transformation temperature/ critical point”, etc.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
FINAL DRAFT International Standard ISO/FDIS 4885:2026(en)
Ferrous materials — Heat treatments — Vocabulary
1 Scope
This document defines important terms used in the heat treatment of ferrous materials.
Annex A provides an alphabetical list of terms defined in this document, as well as their equivalents in
French, German, Russian, Chinese and Japanese.
Table 1 shows the various iron-carbon (Fe-C) phases.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1 General terms
3.1.1
accelerated cooling
method of cooling in the rolling process and which aims at conditioning the crystal structure of steels and
improving the mechanical properties by means of rolling followed by cooling down through the temperature
range for transformation with a greater speed than that of air-cooling
Note 1 to entry: This does not include the cooling method for quenching which merely cools rapidly on a rolling line
using the accelerated cooling equipment.
Note 2 to entry: Cooling for equipment protection, capability compensation of cooling bed, etc are not included in the
accelerated cooling because they do not affect mechanical properties of steel.
Note 3 to entry: Accelerated cooling is frequently used for tubes, forgings and thick plates.
3.1.2
austenitizing
heating (3.1.37) a ferrous material above A or A temperature and soaking (3.1.57) for enough time to form
1 3
partial or complete austenite
Note 1 to entry: Complete austenitizing takes place above A temperature, while partial austenitizing takes place
between A and A temperatures.
1 cm
Note 2 to entry: The minimum temperature and the length of the soaking time required depend on the steel
composition, the initial microstructure and the heating conditions used.
3.1.3
austenitizing temperature
temperature at which the ferrous material is maintained during austenitizing (3.1.2)

3.1.4
bake hardening steel
steel with the ability to gain an increase of yield strength after a plastic pre-strain and a subsequent heat
treatment (3.1.35)
Note 1 to entry: These steels have a good suitability for cold forming and present a high resistance to plastic straining
(which is increased on finished parts during heat treatment (3.1.35) and a good dent resistance.
Note 2 to entry: The usual industrial paint processes are in the region of 170 °C for 20 min.
3.1.5
cast iron
alloy of iron, carbon and silicon where the carbon content is approximately more than 2 %
3.1.6
characteristic cooling curve
diagram showing the variations of cooling rate in the core of a specimen with temperature
Note 1 to entry: Characteristic cooling curve reflects the cooling capacity of a specimen in a cooling medium at
different temperatures.
3.1.7
controlled atmosphere
furnace atmosphere (3.1.31) of which composition can be controlled for the purpose of oxidation or reduction,
carbonization or decarbonization
Note 1 to entry: The main purpose of controlled atmosphere is to effectively carry out thermo-chemical treatment,
such as carburizing and carbonitriding, and to prevent oxidation or decarburization of ferrous materials during
heating.
3.1.8
controlled atmosphere heat treatment
heat treatment carried out in a controlled atmosphere to achieve non-oxidation and non-decarburization, or
carburizing (nitriding) as required
Note 1 to entry: Heat treatment in a protective atmosphere or inert gas is also called protective atmosphere heat
treatment.
3.1.9
controlled cooling
cooling according to the predetermined cooling schedule during heat treatment
3.1.10
controlled rolling
rolling process where rolling temperature and reduction are controlled to achieve enhanced mechanical
properties
EXAMPLE Normalizing rolling (3.1.51), thermomechanical rolling (3.1.64).
Note 1 to entry: Controlled rolling is used for fine grain ferritic steels and for dual-phase steel for obtaining fine-grain
structure.
3.1.11
cooling
decreasing of the temperature of a hot ferrous material, either continuously, discontinuously, gradually, in
one or more steps or interrupted
Note 1 to entry: The medium in which cooling takes place should be specified, e.g. air, oil, water, etc. See also quenching
(3.3.19).
3.1.12
cooling conditions
cooling schedules
condition(s) (temperature and kind of cooling medium, relative movements, agitation, etc.) under which the
cooling (3.1.11) of the ferrous material takes place
3.1.13
cooling function
cooling curve
temperature change at a defined point of a ferrous material or in a furnace load as a function of time during
cooling
Note 1 to entry: The cooling function can be shown as a graph or written in a mathematical formula.
3.1.14
cooling rate
variation in temperature as a function of time during cooling (3.1.11)
Note 1 to entry: A distinction is made between an instantaneous rate corresponding to a specific temperature, and an
average rate over a defined interval of temperature or time.
3.1.15
cooling time
cooling duration
interval of time separating two characteristic temperatures of the cooling function (3.1.13)
Note 1 to entry: It is always necessary to specify precisely what the temperatures are.
3.1.16
critical cooling
cooling necessary to avoid transformation to an undesired microstructure
Note 1 to entry: The cooling course can be characterized by the gradient of temperature or of the cooling rate (3.1.14)
in general or at given temperatures or times.
3.1.17
critical cooling rate
rate corresponding to the critical cooling (3.1.16)
3.1.18
critical diameter
diameter, d, of a cylinder with a length ≥ 3 d, having a structure of a volume fraction of 50 % of martensite
(3.8.22) at the centre after quench hardening (3.3.19) with defined conditions
3.1.19
decomposition of austenite
decomposition of austenite into ferrite (3.8.11) and pearlite (3.8.26) or into ferrite and cementite (3.8.8) or
into bainite (3.8.5) with decreasing temperature
3.1.20
differential heating
heating that generates temperature gradient in a ferrous material purposely
3.1.21
endogas
gas mixture produced by incomplete combustion of hydrocarbons
Note 1 to entry: Composition of endogas is usually: by using methane, about a volume fraction of 20 % of carbon
monoxide, about a volume fraction of 41 % of hydrogen and residual nitrogen; by using propane, about a volume
fraction of 24 % of carbon monoxide, about a volume fraction of 31 % hydrogen and residual nitrogen; by using
vaporised methanol with a volume fraction of 60 % of methanol and 40 % of nitrogen, resulting in a volume fraction of
20 % of carbon monoxide, 40 % of hydrogen and residual nitrogen.

Note 2 to entry: The endogas is used as a basic or carrier gas. Carbon level (3.7.9) of the ferrous material is usual about
a mass fraction of 0,4 %. For higher carbon levels of the ferrous material, it is necessary to add a gas to donate carbon,
e.g. for carburizing.
3.1.22
endothermic atmosphere
furnace atmosphere (3.1.31) produced endothermically and with a carbon potential capable of being matched
to the carbon content of the ferrous material under heat treatment (3.1.35) in order to reduce, increase or
maintain the carbon level (3.7.9) at the surface of the ferrous material
Note 1 to entry: Endothermic means that heat energy is transferred to the atmosphere.
3.1.23
equalization
second stage of heating (3.1.37) of a ferrous material whereby the required temperature is obtained at the
surface throughout its section
Note 1 to entry: See Figure 1.
Key
Y temperature, T
X time, t
1 heating curve of surface
2 heating curve of core
T austenitizing or quenching temperature
t heating up time
t equalization time
t heating time
t soaking time
Figure 1 — Schematic representation of heating during an austenitizing treatment
3.1.24
equilibrium diagram
graphical representation of the temperature and composition limits of phase fields in an alloy system

3.1.25
equivalent diameter
equivalent diameter of cooling rate
ruling section
diameter, d, of a cylinder of the same steel (of length ≥ 3 d) in which the cooling rate (3.1.14) in the core is
identical to the slowest cooling rate recorded in the considered ferrous workpiece with an irregular shape,
under the same cooling conditions (3.1.12)
[1] [2]
Note 1 to entry: The determination of the equivalent diameter is described in ISO 683-1 and ISO 683-2 .
3.1.26
eutectoid transformation
reversible transformation of austenite (3.8.4) into pearlite (3.8.26) (ferrite + cementite) that occurs at a
constant temperature
Note 1 to entry: Temperature for eutectoid transformation of pure iron is 723 °C. Alloying elements or cooling speed
influence this temperature.
3.1.27
exogas
gas mixture produced by complete combustion of hydrocarbons
Note 1 to entry: Composition of exogas is usually a volume fraction of 6,8 % to 10 % of carbon dioxide, 2,4 % to 7,4 % of
carbon monoxide, 2,5 % to 9,5 % of hydrogen, small amounts of oxygen, water vapor, residual nitrogen.
Note 2 to entry: Exogas is used to protect ferrous material surfaces from oxidation and has a decarburizing effect.
3.1.28
exothermic atmosphere
furnace atmosphere (3.1.31) produced exothermically and controlled not oxidizing the ferrous material
Note 1 to entry: Exothermic means that heat energy is transferred from the atmosphere.
3.1.29
ferrous material
metals and alloys with iron as the principal element
Note 1 to entry: Ferrous materials include products and workpieces of steel and cast iron.
3.1.30
fluidized bed
heat treatment (3.1.35) medium made by a ceramic powder fluidized by a gas into a furnace heated from the
outside
Note 1 to entry: The fluidizing gas can be inert to protect the surface of heat-treated ferrous materials or a reactive
gas for a thermochemical treatment (3.7.54) such as carburizing (3.7.13).
3.1.31
furnace atmosphere
gaseous filling of a furnace, used for heat treatment (3.1.35)
Note 1 to entry: Gaseous filling can be pure gas or gas mixture. The atmosphere can be inert or reactive.
Note 2 to entry: The purpose of furnace atmospheres is to prevent oxidation (3.9.11) or decarburization (3.9.2) or to be
the carrier or reactive gas in a thermochemical treatment (3.7.54).
3.1.32
heat conduction
spontaneous heat flow from a body at a higher temperature to a body at a lower temperature and/or within
a ferrous material with locally different temperatures, e.g. between surface and core
Note 1 to entry: In the absence of external drivers, temperature differences decay over time, and the bodies approach
to thermal equilibrium.
3.1.33
heat convection
transfer of heat from one place to another by movement of fluids
Note 1 to entry: Convection is usually the dominant form of heat transfer in liquids and gases.
Note 2 to entry: Heat convection during quenching (3.3.19) can be single phase [as in gas quenching (3.3.7)] or dual
phase [as in water quenching with water and vapor film (3.3.28) at the same time]. Usually, single-phase convection
has a lower heat transfer than dual-phase convection.
3.1.34
heat radiation
thermal radiation
emission of electromagnetic waves from all matter that has a temperature greater than absolute zero
Note 1 to entry: Heat radiation represents a conversion of thermal energy into electromagnetic energy.
3.1.35
heat treatment
series of operations in the course of which a solid ferrous material (3.1.29) is totally or partially exposed to
thermal cycles (3.1.62) to bring about a change in its properties and/or structure
Note 1 to entry: The chemical composition of the ferrous material (3.1.29) can be modified during these operations.
See thermochemical treatment (3.7.54).
3.1.36
heat treatment cycle
entire heat treatment process involving heating, soaking and cooling
3.1.37
heating
increasing of the temperature of a ferrous material, either continuously, discontinuously or gradually, in one
or more steps
Note 1 to entry: The medium in which heating takes place should be specified, e.g. in protective atmosphere, inert gas,
noble gas, vacuum, air, etc.
3.1.38
heating conditions
heating schedules
condition(s) (temperature, time and method of heating, etc.) under which the heating (3.1.37) of the ferrous
material takes place
3.1.39
heating function
heating curve
temperature change at a defined point of a ferrous material or in a furnace load as a function of time during
heating (3.1.37).
Note 1 to entry: The heating function can be shown as a graph or written in a mathematical formula.
3.1.40
heating rate
variation in temperature as a function of time during heating (3.1.37)
Note 1 to entry: A distinction is made between an instantaneous rate corresponding to a specific temperature, and an
average rate over a defined interval of temperature or time.

3.1.41
heating time
heating duration
interval of time separating two characteristic temperatures of the heating function (3.1.39)
Note 1 to entry: It is always necessary to specify precisely what the temperatures are.
Note 2 to entry: Heating time is the sum of heating up time and equalization time.
3.1.42
heating up time
time for the surface of a ferrous material to reach the specified temperature during heating
3.1.43
high energy beam heat treatment
heat treatment using different high power density energy sources, such as laser, electron beam or plasma, to
heat ferrous materials
3.1.44
hot forming
forming of steel products in a temperature range usually between 780 °C up to 1 300 °C depending on the
chemical composition of the workpiece
Note 1 to entry: Hot forming includes hot-rolling, hot-forging, hot-bending, etc.
Note 2 to entry: Forming between the temperatures of hot forming and cold forming is called warm forming.
3.1.45
hypereutectoid steel
steel containing more carbon than the eutectoid composition
3.1.46
hypoeutectoid steel
steel containing less carbon than the eutectoid composition
3.1.47
ideal critical diameter
diameter of a cylinder having a structure of a volume fraction of 50 % of martensite at the centre after
cooling in a medium with ideal condition of quenching intensity (3.3.20)
3.1.48
impulse heating
method of heating (3.1.37) by short repeated bursts of energy, giving rise to a local increase in temperature
Note 1 to entry: Various sources of energy can be used, e.g. condenser discharge, lasers, electron beams, etc.
3.1.49
induction heat treatment
heat treatment using electromagnetic induction to generate eddy current within a ferrous material to heat
the ferrous material
3.1.50
isoforming
thermomechanical control process (3.1.63) of steel consisting of plastic deformation carried out during the
transformation of austenite (3.8.4) to pearlite (3.8.26)
3.1.51
normalizing rolling
controlled rolling (3.1.10) process in which the final deformation is carried out within a certain temperature
range, leading to a material condition equivalent to that obtained after normalizing (3.2.17), such that the
specified mechanical properties are still met in the event of any subsequent normalizing

3.1.52
plasma heat treatment
ion bombardment heat treatment
glow discharge heat treatment
heat treatment using glow discharge generated between a ferrous material (as cathode) and anode in a
specific atmosphere with pressure lower than 0,1 MPa
-1 -3
Note 1 to entry: The pressure is usually 10 Pa to 10 Pa.
3.1.53
preheating
heating of a ferrous material with one or more temperature levels and suitable soaking time until the desired
heat treatment temperature is reached
3.1.54
protective atmosphere
protective gas
gas to avoid the change of composition of the surface layer of ferrous materials during heat treatment
(3.1.35), usually used to produce a protective furnace atmosphere (3.1.31)
Note 1 to entry: Protective gas is usually used to avoid oxidation (3.9.11) or decarburization (3.9.2).
Note 2 to entry: The composition of protective gases depends on the purpose of its use.
Note 3 to entry: Best protection is treatment in vacuum furnaces.
3.1.55
recovery
change in structure and properties from annealing (3.2.1) a cold-worked ferrous material associated with
residual stress removal and strain-free region formation
Note 1 to entry: Recovery is carried out at a temperature below that of recrystallizing (3.1.56).
Note 2 to entry: Recovery is due to dislocation climb and glide produced by the movement of vacancies and atoms.
3.1.56
recrystallization
change in structure and properties from annealing (3.2.1) a cold-worked ferrous material associated with
frequent formation of new fine grains
Note 1 to entry: Grain growth (3.8.17) can occur in the ferrous material under critical degree of deformation.
Note 2 to entry: Recrystallization usually decreases strength and increases ductility.
3.1.57
soaking
part of the thermal cycle (3.1.62) during which the temperature is held constant
Note 1 to entry: It is necessary to stipulate whether the temperature concerned is that of the surface of the ferrous
material, the core or any other particular point on the ferrous material or on the furnace load.
3.1.58
spheroidal graphite iron
cast iron (3.1.5) containing spherical graphite
Note 1 to entry: It differs from the grey cast iron with lamellar graphite in its chemical composition, merely due to the
addition of magnesium (from 0,04 %to 0,06 %), cerium and other rare earth elements that influence the formation of
graphite spheres
Note 2 to entry: Usually nodular cast iron will be heat treated, e.g. austempering (3.3.3), normalizing (3.2.17),
quenching and tempering (3.4.3).

3.1.59
stabilization of retained austenite
phenomenon which reduces or prevents the possibility of the transformation of retained austenite (3.8.31)
into martensite (3.8.22) during cooling (3.1.11) to a temperature below ambient temperature
Note 1 to entry: This stabilization occurs during low temperature tempering or holding at ambient temperature after
quenching (3.3.19).
3.1.60
stabilizing
heat treatment (3.1.35) of a ferrous material intended to prevent subsequent geometrical, dimensional,
microstructural and property changes with time
Note 1 to entry: Generally, stabilizing itself can cause those changes to occur, which at a later date would be undesirable.
3.1.61
steel
ferrous material with iron as the principal element and carbon content not more than a mass fraction of 2 %
Note 1 to entry: The presence of large quantities of carbide-forming elements can modify the upper limit of the carbon
content.
Note 2 to entry: The nomenclature for unalloyed steels suitable for heat treatment (3.1.35) and for alloyed steels is
[3] [4]
defined by ISO 4948-1 and ISO 4948-2 .
3.1.62
thermal cycle
variation of temperature as a function of time during heat treatment (3.1.35)
3.1.63
thermomechanical control process
TMCP
hot forming (3.1.44) process in which the final deformation is carried out in a certain temperature range
followed by air cooling or accelerated cooling
Note 1 to entry: Leading to a material condition with certain properties which can not be achieved or repeated by heat
treatment (3.1.35) alone, thermomechanical control process can include tempering (3.4.8), including self-tempering
(3.4.1) but excluding direct quenching (3.3.5), quenching and tempering (3.4.3).
Note 2 to entry: The target of thermomechanical control process is to produce a fine grain, tough and high tensile
structure which can not be achieved or repeated by heat treatment (3.1.35) alone and improve weldability and
formability of a steel product.
3.1.64
thermomechanical rolling
TMR
rolling process in which the final deformation is carried out in a certain temperature range leading to a
material condition with certain properties which cannot be achieved or repeated by heat treatment alone
Note 1 to entry: Subsequent heating above 580 °C can lower the strength values. If temperature above 580 °C is needed
reference should be made to the supplier.
Note 2 to entry: Thermomechanical rolling leading to the delivery condition TMCP can include processes with
an increasing cooling rate with or without tempering (3.4.8) including self-tempering (3.4.1) but excluding direct
quenching and quenching and tempering.
Note 3 to entry: In some publications, TMR is also considered as a process of TMCP.

3.1.65
thermo-mechanical heat treatment
coupled heat treatment by combining plastic deformation and thermal heat treatment to improve mechanical
properties of a ferrous material
Note 1 to entry: Thermo-mechanical treatment includes hot forming (3.1.44), controlled rolling (3.1.10), etc.
3.1.66
through heating
method of heating that enables the whole workpiece to reach a uniform temperature
3.1.67
transformation diagram
presentation of austenite (3.8.4) transformation of ferrous materials in dependence on time and temperature
for a given steel composition
Note 1 to entry: Set of curves can be drawn in a semi-logarithmic coordinate system with temperature as function of
logarithmic time which define, for each level of temperature, the phase transformation of austenite as beginning and
the transformation to other phases (3.8.27) as ending.
Note 2 to entry: At the end of transformation, the amount of constituents of the microstructure and the hardness can
be determined.
Note 3 to entry: There is distinction between transformation diagrams in relation to the heating and soaking period
called time-temperature austenitization diagram (TTA diagram) (3.1.67.1) and diagrams in relation to the cooling
period called time temperature transformation diagram (TTT diagram) (3.1.67.4).
3.1.67.1
time-temperature austenitization diagram
TTA diagram
diagram which presents austenitization of the initial structure of ferrous material in dependence on time
and temperature for a given steel composition and initial microstructure
Note 1 to entry: There is distinction between isothermal austenitization diagrams (3.1.67.2) and time-temperature
austenitization diagrams.
Note 2 to entry: Set of curves can be drawn in a semi-logarithmic coordinate system with logarithmic time/
temperature coordinates which define, for each level of temperature, the phase transformation of ferrite (3.8.11),
pearlite (3.8.26), carbide as beginning and the transformation to austenite (3.8.4) as ending.
3.1.67.2
isothermal austenitization diagram
IA diagram
diagram which presents transformation of an initial microstructure to austenite at a given temperature in
dependence on time
Note 1 to entry: For a given temperature, the graph is read from left to right following the horizontal temperature line
to find out the required time for transforming each component of the microstructure as beginning and the achieved
austenite microstructure as ending.
Note 2 to entry: Differences in the initial microstructure can modify the diagram.
3.1.67.3
continuous austenitization diagram
diagram which presents transformation of an initial microstructure to austenite at a given heating rate in
dependence on time
Note 1 to entry: Set of curves for different heating rates can be drawn in a semi-logarithmic coordinate system with
logarithmic time/temperature coordinate.
Note 2 to entry: For a given heating rate along the curve, the time and temperature of begin and end of the change of
each component of the initial structure and the austenitic structure can be obtained.
Note 3 to entry: Differences in the initial microstructure can modify the diagram.

3.1.67.4
time-temperature-transformation diagram
TTT diagram
isothermal transformation diagram
IT diagram
diagram which presents isothermal transformation of undercooled austenite (3.8.39)
Note 1 to entry: TTT-diagrams can be used to determine the volume fraction of each phase (3.8.27) and its hardness
after the transformation.
3.1.67.5
continuous-cooling-transformation diagram
CCT diagram
diagram which presents continuous cooling transformation of austenite (3.8.4)
Note 1 to entry: At the 500 °C line, the cooling parameter, λ, divided by 100 or directly in seconds for the temperature
range between 800 °C and 500 °C can be determined.
3.1.68
transformation point
transformation temperature between one microstructures to another
Note 1 to entry: The term shall be completed by indication of the kind of the microstructure, e.g. transformation point
of the martensitic stage, pearlitic stage, etc.
3.1.69
transformation range
interval of temperature within which a ferrous product undergoes a change of phase (3.8.27)
3.1.70
transformation temperature
critical point
temperature at which a change of phase (3.8.27) occurs and, by extension, at which the transformation
begins and ends when the transformation occurs over a range of temperatures
Note 1 to entry: The following principal transformation temperatures can be distinguished in steels:
— A , equilibrium temperature defining the lower limit of existence of austenite (3.8.4);
— A , equilibrium temperature defining the upper limit of existence of ferrite (3.8.11);
— A , equilibrium temperature defining the upper limit of existence of cementite (3.8.8) in hypereutectoid steels
cm
(3.1.45);
— M , temperature at which the austenite begins to transform into martensite (3.8.22) during cooling;
s
— M , temperature at which the austenite has almost completely transformed into martensite during cooling;
f
— M , temperature at which a volume fraction of x % of the austenite has transformed into martensite during cooling.
x
3.1.71
ultrafast cooling
method of cooling which is carried out mainly in the quenching process of thin plates and which aims at
obtaining finer microstructure of steels and improving the mechanical properties by means of high pressure
water cooling with a much greater speed than that of water-cooling
3.1.72
vacuum heat treatment
heat treatment in a vacuum environment with pressure below 0,1 MPa
-1 -3
Note 1 to entry: The pressure is usually 1×10 Pa to 1×10 Pa.

3.1.73
strain hardening
work hardening
strengthening of a ferrous material by deformation
Note 1 to entry: This strengthening occurs because of dislocation movements and dislocation generation within the
crystal structure of the ferrous material.
Note 2 to entry: Work hardened structure can be removed by recrystallization.
3.2 Terms related to annealing and normalizing
3.2.1
annealing
heat treatment (3.1.35) consisting of heating (3.1.37) and soaking (3.1.57) at a suitable temperature followed
by cooling (3.1.11) under conditions such that, after return to ambient temperature, the ferrous material is
in a microstructural state closer to that of equilibrium
Note 1 to entry: Since this definition is very general, it is advisable to use an expression specifying the aim of the
treatment. See, for example, bright annealing (3.2.5), full annealing (3.2.9), softening/soft annealing (3.2.21) inter-
critical annealing (3.2.13), isothermal annealing (3.2.14) and subcritical annealing.
3.2.2
bainitizing
austenitizing (3.1.2) and quenching (3.3.19) to a temperature above M and isothermal soaking to ensure a
s
transformation of the austenite (3.8.4) to upper or lower bainite (3.8.5)
Note 1 to entry: Bainitizing can result in both upper and lower bainites, while austempering usually results in lower
bainite.
3.2.3
baking
hydrogen removal annealing
annealing (3.2.1) below A temperature for a certain soaking time permitting the release of hydrogen
absorbed in a ferrous material without modifying its structure
Note 1 to entry: The soaking time depends on the size of the ferrous material and the hydrogen content.
Note 2 to entry: In quench hardened or case-hardened steels, the hydrogen is usually removed at a tempering
temperature of 230 °C up to 300 °C, with some hours of soaking time.
Note 3 to entry: The treatment is generally carried out following an electrolytic plating or pickling, or a welding
operation.
3.2.4
batch annealing
box annealing
annealing (3.2.1) of strip in tight coil form within a protective atmosphere for a predetermined time-
temperature cycle
3.2.5
bright annealing
annealing (3.2.1) in a medium preventing the oxidization of the surface to maintain the original surface
quality
3.2.6
continuous annealing
annealing (3.2.1) of strips and bars moving continuously through a furnace
Note 1 to entry: The atmosphere used in the furnace should be specified.

3.2.7
diffusion annealing
annealing (3.2.1) of ferrous materials to reduce segregation (3.9.14) and promote homogeneity by diffusion
(3.7.24)
Note 1 to entry: To reduce segregation of metallic alloying elements in steel making or in bar rolling a diffusion
annealing with temperatures between 1 000 °C and 1 300 °C is required.
Note 2 to entry: To reduce segregation of non-metallic alloying elements (e.g. carbon, nitrogen or sulfur) in ferrous
materials a diffusion annealing at a temperature below 1 000 °C would be usually done.
3.2.8
ferrite-pearlite annealing
FP annealing
annealing (3.2.1) consisting of austenitizing (3.1.2) and cooling (3.1.11) down at a relatively slow rate until
decomposition of austenite (3.1.19) is completed
Note 1 to entry: The purpose of ferrite-pearlite annealing is to attain a microstructure with ferrite and pearlite, and to
improve machinability.
3.2.9
full annealing
critical annealing
annealing (3.2.1) to achieve spheroidites (3.8.35) consisting of complete or partial austenitizing (3.1.2)
followed by slow cooling (3.1.11)
Note 1 to entry: The austenitization of hypoeutectoid steel (C content is less than a mass fraction of 0,77 %) takes
place above A temperature (the microstructure is then fully austenitic), however hypereutectoid steels (C content
is more than a mass fraction of 0,77 %) between A and A temperatures (the microstructure is partially austenitic).
1 m
3.2.10
graphitization
precipitation of carbon in the form of graphite
3.2.11
graphitizing
annealing (3.2.1) applied to cast irons (3.1.5) or hypereutectoid steels (3.1.45) to bring about graphitization
(3.2.10)
3.2.12
homogenizing
high-temperature diffusion annealing
prolonged high-temperature annealing (3.2.1) to make the distribution of the chemical composition uniform
in a ferrous material
3.2.13
inter-critical annealing
inter-critical treatment
annealing (3.2.1) of a hypoeutectoid steel (3.1.46) involving heating (3.1.37) to and soaking at a temperature
between A and A , followed by cooling (3.1.11) adapted to the characteristics required
1 3
3.2.14
isothermal annealing
annealing (3.2.1) consisting of austenitizing (3.1.2) and cooling (3.1.11) down to a certain temperature which
is held constant until decomposition of austenite (3.1.19) is completed
EXAMPLE Isothermal pearlite transformation or isothermal bainitizing (3.2.2).

3.2.15
isothermal normalizing
normalizing in which austenitized ferrous workpieces are fast cooled by a forced air blowing to and soaking
at a certain temperature in the pearlitic transformation zone in order to obtain the pearlitic microstructure,
and then cooled in air
Note 1 to entry: Isothermal normalizing is differentiated by cooling rate and form of pearlite attained with isothermal
annealing.
3.2.16
malleablizing
long-time annealing (3.2.1) at high temperatures to change the structure of white cast iron (3.1.5) to produce
malleable cast iron
Note 1 to entry: If the annealing is done in a decarburizing (3.7.21) atmosphere, the malleable cast iron is called “white
malleable cast iron”. If the annealing atmosphere is not decarburizing so that elementary carbon is formed as graphite,
the iron is called “black malleable cast iron”.
3.2.17
normalizing
heat treatment (3.1.35) intended to attain both grain refinement and homogenization of a ferrous material,
consisting of heating (3.1.37) it to a temperature slightly above A [A for hypereutectoid steels (3.1.45)], and
3 1
then cooling (3.1.11) it in air to a temperature substantially below the transformation range to obtain a fine
ferrite-pearlite structure
Note 1 to entry: Normalizing leads to the formation of new grains and acts as a refinement of the microstructure.
3.2.18
patenting
heat treatment (3.1.35) consisting of austenitizing (3.1.2) followed by cooling (3.1.11) under conditions
suitable for producing pearlite with a fine interlamellar spacing for subsequent wire-drawing or cold-rolling
Note 1 to entry: The cooling medium in which patenting takes place should be specified, e.g. air, salt bath, etc.
Note 2 to entry: The patenting method should be specified with the word “continuous” if the operation is to be carried
out continuously on the unwound ferrous material, or “batch” (discontinuously) if the material is to be handled as one
load and remains in the form of a coil or bundle. In the case of continuous processing, it is also called “inline patenting”.
3.2.19
recrystallization annealing
annealing (3.2.1) to remove strengthening after cold forming leading to the formation of new grains by
nucleation without any change in phase (3.8.27)
Note 1 to entry: Grain growth (3.8.17) can occur in the ferrous material under critical degree of deformation.
3.2.20
repeated normalizing
normalizing on ferrous materials for two or more times
Note 1 to entry: Repeated normalizing is mainly applied for castings and forgings.
3.2.21
soft annealing
softening
annealing (3.2.1) intended to reduce the hardness of the ferrous material to a given level
Note 1 to entry: Soft annealing slightly below A temperature is called subcritical annealing.
ISO/FDIS 4
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