ISO/FDIS 4885

Ferrous materials — Heat treatments — Vocabulary

ISO 4885:2018 defines important terms used in the heat treatment of ferrous materials. NOTE The term ferrous materials include products and workpieces of steel and cast iron. Annex A provides an alphabetical list of terms defined in this document, as well as their equivalents in French, German, Chinese and Japanese. Table 1 shows the various iron-carbon (Fe-C) phases.

Matériaux ferreux — Traitements thermiques — Vocabulaire

ISO 4885:2018 définit les termes importants utilisés dans le traitement thermique des matériaux ferreux. NOTE Le terme matériaux ferreux inclut les produits et les pièces en acier et en fonte. L'Annexe A donne une liste alphabétique des termes définis dans ce document ainsi que leurs équivalents en anglais, allemand, chinois et japonais. Le Tableau 1 montre les différentes phases fer-carbone (Fe-C).

General Information

• Status: Not Published
• ICS: 01.040.25 - Manufacturing engineering (Vocabularies)
• ICS: 01.040.77 - Metallurgy (Vocabularies)
• ICS: 25.200 - Heat treatment
• ICS: 77.140.01 - Iron and steel products in general
• Technical Committee: ISO/TC 17 - Steel
• Drafting Committee: ISO/TC 17 - Steel
• Current Stage: 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
• Start Date: 29-Apr-2026
• Completion Date: 29-Apr-2026

Relations

• Consolidates: FprEN ISO 4885 - Ferrous materials - Heat treatments - Vocabulary (ISO/FDIS 4885:2026)
• Effective Date: 12-Feb-2026
• Revises: ISO 4885:2018 - Ferrous materials — Heat treatments — Vocabulary
• Effective Date: 07-Sep-2023

Overview

ISO/FDIS 4885:2026 (Ferrous materials - Heat treatments - Vocabulary) is an international standard developed by ISO that provides a comprehensive set of standardized terms and definitions for heat treatment processes applied to ferrous materials, including both steel and cast iron. This standard is essential for ensuring consistent communication and understanding across industries and geographic regions by establishing a common vocabulary. It serves stakeholders in the steel industry, metallurgy, manufacturing, engineering, and research who require clarity and precision when referring to heat treatment of ferrous materials.

ISO/FDIS 4885:2026 supersedes the earlier ISO 4885:2018 edition, introducing several new terms, restructuring the categories, and updating existing vocabulary to match advancements in material science and industrial processes.

Key Topics

ISO/FDIS 4885:2026 organizes the vocabulary into key categories, each addressing different aspects of heat treatments for ferrous materials:

• General Terms: Fundamental definitions such as accelerated cooling, austenitizing, and the types of ferrous materials (steel and cast iron).
• Annealing and Normalizing: Terms related to softening treatments and normalization processes.
• Quenching: Vocabulary for rapid cooling processes intended to modify the microstructure of steel and cast iron.
• Tempering and Partitioning: Definitions for processes used to adjust toughness, hardness, and other mechanical properties after initial heat treatment.
• Ageing: Terms describing treatments that affect the time-dependent properties of ferrous materials.
• Surface Heat Treatment: Words specific to localized or surface-specific thermal treatments, such as induction heating or plasma heat treatment.
• Thermochemical Treatment: Vocabulary for processes that involve both thermal exposure and chemical changes to surfaces (e.g., carburizing, nitriding).
• Structure: Definitions relating to phase transformations, microstructural constituents, and metallurgical diagrams like TTT (time-temperature-transformation) and CCT (continuous-cooling-transformation).
• Defects: Terms describing potential faults or undesirable transformations that can occur during heat treatment.

Additionally, the standard provides an alphabetical annex listing all terms, including equivalents in French, German, Russian, Chinese, and Japanese, supporting global harmonization.

Applications

ISO/FDIS 4885:2026 offers practical value in a wide range of industrial and research scenarios:

• Steel Manufacturing & Processing: Ensures clear communication between producers, engineers, and customers about heat treatment protocols, expected outcomes, and quality requirements.
• Metallurgical Testing: Standardizes terminology used in reporting results and performing comparative analyses of microstructures and mechanical properties.
• Product Design & Specification: Provides precise definitions that support materials selection, design for manufacturability, and engineering documentation.
• Quality Assurance: Supports the alignment of testing criteria, inspection procedures, and acceptance standards in accordance with global best practices.
• Cross-border Projects: Harmonizes communication in international supply chains by offering multilingual equivalents, reducing the risk of misinterpretation.
• Research and Development: Facilitates reproducibility and clarity when documenting, publishing, or reviewing material science experiments.

Related Standards

The terminology defined in ISO/FDIS 4885:2026 is closely connected to other key international standards, which together form a robust framework for heat treatment of ferrous materials:

• ISO 4948-1 and ISO 4948-2: Define nomenclature and classification of steels.
• ISO 683 series: Cover heat-treatable steels, alloy steels, and tool steels, including references for equivalent diameter and cooling conditions.
• ISO Online Browsing Platform: Central repository for up-to-date standardized terminology.
• IEC Electropedia: Extensive electrical and thermal engineering vocabulary resource.

Adopting ISO/FDIS 4885:2026 helps ensure global consistency in technical documentation and supports the successful implementation of quality heat treatment practices across the ferrous materials industry.

Standards Content (Sample)

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
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.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/CEN PARALLEL PROCESSING LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
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
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/CEN PARALLEL PROCESSING
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
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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Any trade name used in this document is information given for the convenience of users and does not
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related to conformity assessment, as well as information about ISO's adherence to the World Trade
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
...

ISO/TC 17
Secretariat: JISC
ISO TC 17/WG 29
Date: 2026-03-1104-14
Ferrous materials — Heat treatments — Vocabulary
This draft is submitted to a parallel vote in ISO, CEN.

Matériaux ferreux — Traitements thermiques — Vocabulaire
FDIS stage
This draft is submitted to a parallel vote in ISO, CEN.

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying,
or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
at the address below or ISO’s member body in the country of the requester.
ISO copyright office
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Tel.Phone: + 41 22 749 01 11
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Published in Switzerland
iii
Contents
Foreword . v
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 . 14
3.3 Terms related to quenching . 17
3.4 Terms related to tempering and partitioning . 21
3.5 Terms related to ageing . 23
3.6 Terms related to surface heat treatment . 24
3.7 Terms related to thermochemical treatment . 26
3.8 Terms related to structure . 38
3.9 Terms related to defects . 44
Annex A (informative) Equivalent terms . 48
Bibliography . 78
Index 79
Table of contents
Foreword
Table of contents . 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 . 14
3.3 Terms related to quenching . 17
3.4 Terms related to tempering and partitioning . 22
3.5 Terms related to ageing . 24
3.6 Terms related to surface heat treatment . 25
3.7 Terms related to thermochemical treatment . 26
3.8 Terms related to structure . 37
3.9 Terms related to defects . 43
Annex A (informative) Equivalent terms . 47
Bibliography . 65
iv
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 this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
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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.
v
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.
vi
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 AAnnex A provides an alphabetical list of terms defined in this document, as well as their equivalents
in French, German, Russian, Chinese and Japanese.
Table 1Table 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 terminologicalterminology 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 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 3.1.2
austenitizing
heating (3.1.37(3.1.37)) a ferrous material above A or A temperature and soaking (3.1.57(3.1.57)) for
1 3
enough time to form partial or complete austenite
Note 1 to entry: Complete austenitizing takes place above A3 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 3.1.3
austenitizing temperature
temperature at which the ferrous material is maintained during austenitizing (3.1.2(3.1.2))
3.1.4 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(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(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 3.1.5
cast iron
alloy of iron, carbon and silicon where the carbon content is approximately more than 2 %
3.1.6 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 3.1.7
controlled atmosphere
furnace atmosphere (3.1.31(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 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 3.1.9
controlled cooling
cooling according to the predetermined cooling schedule during heat treatment
3.1.10 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(3.1.73),), thermomechanical rolling (3.1.64(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 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(3.3.19).).
3.1.12 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(3.1.11)) of the ferrous material takes place
3.1.13 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 3.1.14
cooling rate
variation in temperature as a function of time during cooling (3.1.11(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 3.1.15
cooling time
cooling duration
interval of time separating two characteristic temperatures of the cooling function (3.1.13(3.1.13))
Note 1 to entry: It is always necessary to specify precisely what the temperatures are.
3.1.16 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(3.1.14)) in general or at given temperatures or times.
3.1.17 3.1.17
critical cooling rate
rate corresponding to the critical cooling (3.1.16(3.1.16))
3.1.18 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(3.8.22)) at the centre after quench hardening (3.3.19(3.3.18)) with defined conditions
3.1.19 3.1.19
decomposition of austenite
decomposition of austenite into ferrite (3.8.11(3.8.11)) and pearlite (3.8.26(3.8.26)) or into ferrite and
cementite (3.8.8(3.8.8)) or into bainite (3.8.5(3.8.5)) with decreasing temperature
3.1.20 3.1.20
differential heating
heating that generates temperature gradient in a ferrous material purposely
3.1.21 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(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 3.1.22
endothermic atmosphere
furnace atmosphere (3.1.31(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(3.1.35)) in order to
reduce, increase or maintain the carbon level (3.7.9(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 3.1.23
equalization
second stage of heating (3.1.37(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 1Figure 1.
Key
AY temperature, T
X time, t
1 heating curve of surface
B2 heating curve of core
T1 austenitizing or quenching temperature
t time
t1 heating up time
t2 equalization time
t3 heating time
t soaking time
T temperature
T austenitizing or quenching temperature
Figure 1— Schematic representation of heating during an austenitizing treatment
3.1.24 3.1.24
equilibrium diagram
graphical representation of the temperature and composition limits of phase fields in an alloy system
3.1.25 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(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(3.1.12))
[1][i] [2] [ii]
Note 1 to entry: The determination of the equivalent diameter is described in ISO 683-1 and ISO 683-2 .
3.1.26 3.1.26
eutectoid transformation
reversible transformation of austenite (3.8.4(3.8.4)) into pearlite (3.8.26(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 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 3.1.28
exothermic atmosphere
furnace atmosphere (3.1.31(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 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 3.1.30
fluidized bed
heat treatment (3.1.35(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(3.7.56)) such as carburizing (3.7.13(3.7.13).).
3.1.31 3.1.31
furnace atmosphere
gaseous filling of a furnace, used for heat treatment (3.1.35(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(3.9.11)) or decarburization
(3.9.2(3.9.2)) or to be the carrier or reactive gas in a thermochemical treatment (3.7.54(3.7.56).).
3.1.32 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 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(3.3.19)) can be single phase ([as in gas quenching
(3.3.7(3.3.7)))] or dual phase ([as in water quenching with water and vapor film (3.3.28(3.3.28)) at the same time).].
Usually, single-phase convection has a lower heat transfer than dual-phase convection.
3.1.34 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 3.1.35
heat treatment
series of operations in the course of which a solid ferrous material (3.1.29(3.1.29)) is totally or partially
exposed to thermal cycles (3.1.62(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(3.1.29)) can be modified during these
operations. See thermochemical treatment (3.7.54(3.7.56).).
3.1.36 3.1.36
heat treatment cycle
entire heat treatment process involving heating, soaking and cooling
3.1.37 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 3.1.38
heating conditions
heating schedules
condition(s) (temperature, time and method of heating, etc.) under which the heating (3.1.37(3.1.37)) of the
ferrous material takes place
3.1.39 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(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 3.1.40
heating rate
variation in temperature as a function of time during heating (3.1.37(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 3.1.41
heating time
heating duration
interval of time separating two characteristic temperatures of the heating function (3.1.39(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 3.1.42
heating up time
time for the surface of a ferrous material to reach the specified temperature during heating
3.1.43 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 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 3.1.45
hypereutectoid steel
steel containing more carbon than the eutectoid composition
3.1.46 3.1.46
hypoeutectoid steel
steel containing less carbon than the eutectoid composition
3.1.47 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(3.3.20))
3.1.48 3.1.48
impulse heating
method of heating (3.1.37(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 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 3.1.50
isoforming
thermomechanical control process (3.1.63(3.1.63)) of steel consisting of plastic deformation carried out during
the transformation of austenite (3.8.4(3.8.4)) to pearlite (3.8.26(3.8.26))
3.1.51 3.1.51
normalizing rolling
controlled rolling (3.1.10(3.1.73)) 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(3.2.17),), such that the specified mechanical properties are still met in the event of any subsequent
normalizing
3.1.52 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
-1 -3
atmosphere with pressure lower than 0,1 MPa (usually 10 Pa - 10 Pa)
-1 -3
3.1.53Note 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 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(3.1.35),), usually used to produce a protective furnace atmosphere (3.1.31(3.1.31))
Note 1 to entry: Protective gas is usually used to avoid oxidation (3.9.11(3.9.11)) or decarburization (3.9.2(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 3.1.55
recovery
change in structure and properties from annealing (3.2.1(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(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 3.1.56
recrystallization
change in structure and properties from annealing (3.2.1(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(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 3.1.57
soaking
part of the thermal cycle (3.1.62(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 3.1.58
spheroidal graphite iron
cast iron (3.1.5(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 1 2 to entry: Usually nodular cast iron will be heat treated, e.g. austempering (3.3.3(3.3.3),), normalizing
(3.2.17(3.2.17),), quenching and tempering (3.4.3(3.4.8).).
3.1.59 3.1.59
stabilization of retained austenite
phenomenon which reduces or prevents the possibility of the transformation of retained austenite
(3.8.31(3.8.31)) into martensite (3.8.22(3.8.22)) during cooling (3.1.11(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(3.3.19).).
3.1.60 3.1.60
stabilizing
heat treatment (3.1.35(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 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(3.1.35)) and for alloyed steels
[3][iii] [4] [iv]
is defined by ISO 4948-1 and ISO 4948-2 .
3.1.62 3.1.62
thermal cycle
variation of temperature as a function of time during heat treatment (3.1.35(3.1.35))
3.1.63 3.1.63
thermomechanical control process
TMCP
hot forming (3.1.44(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(3.1.35)) alone, thermomechanical control process can include tempering (3.4.8(3.4.8),), including self-
tempering (3.4.1(3.4.1)) but excluding direct quenching (3.3.5(3.3.5),), quenching and tempering (3.4.3(3.4.8).).
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(3.1.35)) alone and improve weldability and
formability of a steel product.
3.1.64 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(3.4.8)) including self-tempering (3.4.1(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 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(3.1.44),), controlled rolling (3.1.10(3.1.10),),
etc.
3.1.66 3.1.66
through heating
method of heating that enables the whole workpiece to reach a uniform temperature
3.1.67 3.1.67
transformation diagram
presentation of austenite (3.8.4(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(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(3.1.67.1)) and diagrams in relation to the
cooling period called time temperature transformation diagram (TTT diagram) (3.1.67.4(3.1.67.4).).
3.1.67.1 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(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(3.8.11),), pearlite
(3.8.26(3.8.26),), carbide as beginning and the transformation to austenite (3.8.4(3.8.4)) as ending.
3.1.67.2 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 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 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(3.8.39))
Note 1 to entry: TTT-diagrams can be used to determine the volume fraction of each phase (3.8.27(3.8.27)) and its
hardness after the transformation.
3.1.67.5 3.1.67.5
continuous-cooling-transformation diagram
CCT diagram
diagram which presents continuous cooling transformation of austenite (3.8.4(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 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 3.1.69
transformation range
interval of temperature within which a ferrous product undergoes a change of phase (3.8.27(3.8.27))
3.1.70 3.1.70
transformation temperature
critical point
temperature at which a change of phase (3.8.27(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(3.8.4););
— — A , equilibrium temperature defining the upper limit of existence of ferrite (3.8.11(3.8.11););
— — Acm, equilibrium temperature defining the upper limit of existence of cementite (3.8.8(3.8.8)) in hypereutectoid
steels (3.1.45(3.1.45););
— — M , temperature at which the austenite begins to transform into martensite (3.8.22(3.8.22)) during cooling;
s
— — M , temperature at which the austenite has almost completely transformed into martensite during cooling;
f
— — Mx, temperature at which a volume fraction of x % of the austenite has transformed into martensite during
cooling.
3.1.71 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 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 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 3.2.1
annealing
heat treatment (3.1.35(3.1.35)) consisting of heating (3.1.37(3.1.37)) and soaking (3.1.57(3.1.57)) at a suitable
temperature followed by cooling (3.1.11(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 e.g.,, for example, bright annealing (3.2.5(3.2.4),), full annealing (3.2.9(3.2.8),), softening/soft annealing
(3.2.21(3.2.21)) inter-critical annealing (3.2.13(3.2.13),), isothermal annealing (3.2.14(3.2.14)) and subcritical annealing.
3.2.2 3.2.2
bainitizing
austenitizing (3.1.2(3.1.2)) and quenching (3.3.19(3.3.19)) to a temperature above M and isothermal soaking
s
to ensure a transformation of the austenite (3.8.4(3.8.4)) to upper or lower bainite (3.8.5(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 3.2.3
baking
hydrogen removal annealing
annealing (3.2.1(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 3.2.4
batch annealing
box annealing
annealing (3.2.1(3.2.1)) of strip in tight coil form within a protective atmosphere for a predetermined time-
temperature cycle
3.2.5 3.2.5
bright annealing
annealing (3.2.1(3.2.1)) in a medium preventing the oxidization of the surface to maintain the original surface
quality
3.2.6 3.2.6
continuous annealing
annealing (3.2.1(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 3.2.7
diffusion annealing
annealing (3.2.1(3.2.1)) of ferrous materials to reduce segregation (3.9.14(3.9.14)) and promote homogeneity
by diffusion (3.7.24(3.7.25))
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 3.2.8
ferrite-pearlite annealing
FP annealing
annealing (3.2.1(3.2.1)) consisting of austenitizing (3.1.2(3.1.2)) and cooling (3.1.11(3.1.11)) down at a
relatively slow rate until decomposition of austenite (3.1.19(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 3.2.9
full annealing
critical annealing
annealing (3.2.1(3.2.1)) to achieve spheroidites (3.8.35(3.8.35)) consisting of complete or partial austenitizing
(3.1.2(3.1.2)) followed by slow cooling (3.1.11(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 3.2.10
graphitization
precipitation of carbon in the form of graphite
3.2.11 3.2.11
graphitizing
annealing (3.2.1(3.2.1)) applied to cast irons (3.1.5(3.1.5)) or hypereutectoid steels (3.1.45(3.1.45)) to bring
about graphitization (3.2.10(3.2.9))
3.2.12 3.2.12
homogenizing
high-temperature diffusion annealing
prolonged high-temperature annealing (3.2.1(3.2.1)) to make the distribution of the chemical composition
uniform in a ferrous material
3.2.13 3.2.13
inter-critical annealing
inter-critical treatment
annealing (3.2.1(3.2.1)) of a hypoeutectoid steel (3.1.46(3.1.46)) involving heating (3.1.37(3.1.37)) to and
soaking at a temperature between A and A , followed by cooling (3.1.11(3.1.11)) adapted to the
1 3
characteristics required
3.2.14 3.2.14
isothermal annealing
annealing (3.2.1(3.2.1)) consisting of austenitizing (3.1.2(3.1.2)) and cooling (3.1.11(3.1.11)) down to a certain
temperature which is held constant un
...

PROJET FINAL
Norme
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ISO/TC 17
Matériaux ferreux — Traitements
Secrétariat: JISC
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Début de vote:
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2026-06-24
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PROJET FINAL
Norme
internationale
ISO/TC 17
Matériaux ferreux — Traitements
Secrétariat: JISC
thermiques — Vocabulaire
Début de vote:
Ferrous materials — Heat treatments — Vocabulary
2026-04-29
Vote clos le:
2026-06-24
LES DESTINATAIRES DU PRÉSENT PROJET SONT
INVITÉS À PRÉSENTER, AVEC LEURS OBSERVATIONS,
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ii
Sommaire Page
Avant-propos .iv
1 Domaine d’application . 1
2 Références normatives . 1
3 Termes et définitions . 1
3.1 Termes généraux .1
3.2 Termes relatifs au recuit et à la normalisation . 13
3.3 Termes relatifs à la trempe .16
3.4 Termes relatifs au revenu et au partitionnement . 20
3.5 Termes relatifs au vieillissement . 22
3.6 Termes relatifs au traitement thermique de surface . 23
3.7 Termes relatifs au traitement thermochimique .24
3.8 Termes relatifs à la structure . 34
3.9 Termes relatifs aux défauts . 39
Annexe A (informative) Termes équivalents .43
Bibliographie .62
Index .63

iii
Avant-propos
L’ISO (Organisation internationale de normalisation) est une fédération mondiale d’organismes nationaux
de normalisation (comités membres de l’ISO). L’élaboration des Normes internationales est en général
confiée aux comités techniques de l’ISO. Chaque comité membre intéressé par une étude a le droit de faire
partie du comité technique créé à cet effet. Les organisations internationales, gouvernementales et non
gouvernementales, en liaison avec l’ISO participent également aux travaux. L'ISO collabore étroitement avec
la Commission électrotechnique internationale (IEC) en ce qui concerne la normalisation électrotechnique.
Les procédures utilisées pour élaborer le présent document et celles destinées à sa mise à jour sont
décrites dans les Directives ISO/IEC, Partie 1. Il convient, en particulier de prendre note des différents
critères d'approbation requis pour les différents types de documents ISO. Le présent document a
été rédigé conformément aux règles de rédaction données dans les Directives ISO/IEC, Partie 2 (voir
www.iso.org/directives).
L'attention est appelée sur le fait que certains des éléments du présent document peuvent faire l'objet de
droits de propriété intellectuelle ou de droits analogues. L’ISO ne saurait être tenue pour responsable de ne
pas avoir identifié de tels droits de propriété et averti de leur existence. Les détails concernant les références
aux droits de propriété intellectuelle ou autres droits analogues identifiés lors de l'élaboration du document
sont indiqués dans l'Introduction et/ou dans la liste des déclarations de brevets rédigées par l’ISO (voir
www.iso.org/patents).
Les appellations commerciales éventuellement mentionnées dans le présent document sont données pour
information, par souci de commodité, à l’intention des utilisateurs et ne sauraient constituer un engagement.
Pour une explication de la nature volontaire des normes, de la signification des termes et expressions
spécifiques de l’ISO liés à l’évaluation de la conformité, ou pour toute autre information au sujet de l’adhésion
de l’ISO aux principes de l’Organisation mondiale du commerce (OMC) concernant les obstacles techniques
au commerce (OTC), voir le lien suivant: www.iso.org/iso/foreword.html.
Le présent document a été élaboré par le comité technique ISO/TC 17, Acier, en collaboration avec le sous-
comité technique CEN/TC 459/SC 12, Généralités, du Comité européen de normalisation (CEN) conformément
à l’Accord de coopération technique entre l’ISO et le CEN (Accord de Vienne).
Cette quatrième édition annule et remplace la troisième (ISO 4885:2018), qui a fait l’objet d’une révision
technique.
Les principales modifications sont les suivantes:
— la liste des termes a été restructurée et classée en 9 catégories: généralités, recuit et normalisation,
trempe, revenu et partitionnement, vieillissement, traitement thermique de surface, traitement
thermochimique, structure, défauts;
— 66 nouveaux termes ont été ajoutés, tels que «diagramme d'austénitisation continue», «austénite
expansée», «partitionnement», «épaisseur totale de la profondeur de durcissement superficiel», etc.;
— 9 termes ont été supprimés, tels que «structure aciculaire», «acier ferritique», «température de trempe»,
etc.;
— 4 termes ont été intégrés, à savoir «recuit de cuisson/recuit de déshydrogénation», «diagramme de
transformation en refroidissement continu/diagramme CCT»;
— 3 termes ont été subdivisés en 6 nouveaux termes, à savoir «nitruration à blanc/nitrocarburation à
blanc», «surchauffe», «traitement par le froid/traitement cryogénique (anciennement traitement par le
froid)»;
— 39 termes ont été complétés par des synonymes tels que «fonction de refroidissement/courbe de
refroidissement», «blackening/blacking (brunissage)», «température de transformation/point critique»,
etc.
iv
Il convient que l’utilisateur adresse tout retour d’information ou toute question concernant le présent
document à l’organisme national de normalisation de son pays. Une liste exhaustive desdits organismes se
trouve à l’adresse www.iso.org/fr/members.html.

v
PROJET FINAL Norme internationale ISO/FDIS 4885:2026(fr)
Matériaux ferreux — Traitements thermiques — Vocabulaire
1 Domaine d’application
Le présent document définit les termes importants utilisés dans le traitement thermique des matériaux
ferreux.
L’Annexe A donne une liste alphabétique des termes définis dans le présent document ainsi que leurs
équivalents en Anglais, Allemand, Russe, Chinois et Japonais.
Le Tableau 1 indique les différentes phases fer-carbone (Fe-C).
2 Références normatives
Les documents suivants sont cités dans le texte de sorte qu'ils constituent, pour tout ou partie de leur
contenu, des exigences du présent document. Pour les références datées, seule l'édition citée s'applique. Pour
les références non datées, la dernière édition du document de référence s'applique (y compris les éventuels
amendements).
ISO 18203:2016, Acier — Détermination de l’épaisseur des couches durcies superficielles
3 Termes et définitions
L’ISO et l’IEC tiennent à jour des bases de données terminologiques destinées à être utilisées en normalisation,
consultables aux adresses suivantes:
— IEC Electropedia: disponible à l’adresse https:// www .electropedia .org/
— ISO Online browsing platform: disponible à l’adresse https:// www .iso .org/ obp
3.1 Termes généraux
3.1.1
refroidissement accéléré
mode de refroidissement appliqué au cours du procédé de laminage dans le but de conditionner la
structure cristalline des aciers et d’améliorer les propriétés mécaniques au moyen d’un laminage suivi d’un
refroidissement sur une gamme de température accélérant la vitesse de transformation par rapport à un
refroidissement à l’air
Note 1 à l'article: Le mode de refroidissement utilisé pour une trempe n’est pas un mode de refroidissement rapide car
il utilise des équipements de refroidissement accéléré pour assurer un simple refroidissement rapide sur une ligne de
laminage.
Note 2 à l'article: Le refroidissement destiné à assurer la protection des équipements, la compensation de capacité du
refroidissoir, etc., ne sont pas des modes de refroidissement accéléré car ils n’affectent pas les propriétés mécaniques
de l’acier.
Note 3 à l'article: Le refroidissement accéléré est souvent utilisé pour les tubes, les pièces forgées et les plaques
épaisses.
3.1.2
austénitisation
chauffage (3.1.37) d’un matériau ferreux au-delà de la température A ou A et maintien à température
1 3
(3.1.57) pendant une durée suffisante pour former de l’austénite partielle ou complète
Note 1 à l'article: L’austénitisation est complète au-delà de la température A , alors qu’elle n’est que partielle entre les
températures A et A .
1 cm
Note 2 à l'article: La température minimale et la durée de maintien à température requises dépendent de la composition
de l’acier, de la microstructure initiale et des conditions de chauffage utilisées.
3.1.3
température d’austénitisation
température à laquelle le matériau ferreux est maintenu au cours de l’austénitisation (3.1.2)
3.1.4
acier à bake hardening
acier qui présente la capacité d’augmenter sa résistance mécanique après une déformation plastique et un
traitement thermique (3.1.35)
Note 1 à l'article: Ces aciers ont une bonne aptitude au formage à froid et présentent une résistance élevée à la
déformation plastique (qui est augmentée sur les pièces finies lors du traitement thermique (3.1.35)) et une bonne
résistance à d’indentation.
Note 2 à l'article: Les procédés industriels courants de peinture s'effectuent à environ 170 °C pendant 20 min.
3.1.5
fonte
alliage fer-carbone-silicium dont la teneur en carbone est approximativement supérieure à 2 %
3.1.6
courbe caractéristique de refroidissement
diagramme montrant les variations de vitesse de refroidissement dans le cœur d’un échantillon en fonction
de la température
Note 1 à l'article: La courbe caractéristique de refroidissement reflète la capacité de refroidissement d’un échantillon
dans un milieu de refroidissement à différentes températures.
3.1.7
atmosphère contrôlée
atmosphère de four (3.1.31) dont la composition peut être contrôlée à des fins d’oxydation ou de réduction, de
carbonisation ou de décarbonisation
Note 1 à l'article: L’atmosphère contrôlée a pour but principal d’effectuer un traitement thermochimique, tel qu’une
cémentation ou une carbonitruration, de façon efficace et d’empêcher l’oxydation ou la décarburation des matériaux
ferreux au cours du chauffage.
3.1.8
traitement thermique sous atmosphère contrôlée
traitement thermique réalisé sous atmosphère contrôlée afin d’obtenir une non-oxydation et une non-
décarburation, ou une cémentation (nitruration) lorsque cela est requis
Note 1 à l'article: Un traitement thermique dans une atmosphère protectrice ou un gaz inerte est également qualifié de
traitement thermique sous atmosphère contrôlée.
3.1.9
refroidissement contrôlé
refroidissement effectué selon le programme de refroidissement prédéterminé au cours du traitement
thermique
3.1.10
laminage contrôlé
procédé de laminage dans lequel la température de laminage et la réduction d’épaisseur sont contrôlées afin
d’obtenir des caractéristiques mécaniques améliorées
EXEMPLE Laminage normalisant (3.1.73), laminage thermomécanique (3.1.64)
Note 1 à l'article: Le laminage contrôlé est utilisé pour les aciers ferritiques à grains fins et pour les aciers biphasés
afin d’obtenir une structure à grains fins.
3.1.11
refroidissement
réduction de la température d’un matériau ferreux chaud, de façon continue, discontinue, progressive, en
une ou plusieurs phases, ou interrompue
Note 1 à l'article: II convient de préciser le milieu dans lequel le refroidissement est réalisé (par exemple air, huile, eau,
etc.). Voir aussi trempe (3.3.19).
3.1.12
mode de refroidissement
programme de refroidissement
conditions (nature et température du milieu de refroidissement, mouvements relatifs, agitation, etc.) dans
lesquelles s’effectue le refroidissement (3.1.11) du matériau ferreux
3.1.13
loi de refroidissement
courbe de refroidissement
variation de la température en un point défini d’un matériau ferreux ou dans une charge de four, en fonction
du temps, au cours du refroidissement
Note 1 à l'article: La loi de refroidissement peut être représentée sous la forme d’un graphique ou d’une formule
mathématique.
3.1.14
vitesse de refroidissement
variation de la température en fonction du temps au cours du refroidissement (3.1.11)
Note 1 à l'article: Il faut distinguer la vitesse instantanée correspondant à une température spécifiée, de la vitesse
moyenne sur un intervalle de température ou de temps défini.
3.1.15
durée de refroidissement
intervalle de temps séparant deux températures caractéristiques de la loi de refroidissement (3.1.13)
Note 1 à l'article: II est toujours nécessaire de spécifier précisément quelles sont ces températures.
3.1.16
refroidissement critique
refroidissement nécessaire pour éviter la transformation en une microstructure indésirable
Note 1 à l'article: L’intervalle de refroidissement peut être caractérisé par le gradient de température ou la vitesse de
refroidissement (3.1.14) en général ou à des températures ou des temps donnés.
3.1.17
vitesse de refroidissement critique
vitesse de refroidissement correspondant au refroidissement critique (3.1.16)
3.1.18
diamètre critique de trempe
diamètre (d) d’un cylindre de longueur ≥ 3 d présentant au centre une structure d’une fraction volumique de
50 % en martensite (3.8.22) après une trempe (3.3.18) réalisée dans des conditions définies

3.1.19
décomposition de l’austénite
décomposition de l’austénite en ferrite (3.8.11) et perlite (3.8.26) ou en ferrite et cémentite (3.8.8) ou en
bainite (3.8.5) avec la baisse de la température
3.1.20
chauffage différentiel
chauffage qui engendre un gradient de température dans un matériau ferreux de façon délibérée
3.1.21
endogaz
mélange de gaz produit par combustion incomplète d’hydrocarbures
Note 1 à l'article: La composition de l’endogaz est généralement: en cas d’utilisation de méthane, d’une fraction
volumique de 20 % environ de monoxyde de carbone, d’une fraction volumique de 41 % environ d’hydrogène et d’azote
résiduel; en cas d’utilisation de propane, d’une fraction volumique de 24 % environ de monoxyde de carbone, d’une
fraction volumique de 31 % environ d’hydrogène et d’azote résiduel; en cas d’utilisation du méthanol vaporisé avec
une fraction volumique de 60 % de méthanol et 40 % d’azote, produisant une fraction volumique de 20 % de monoxyde
de carbone, 40 % d’hydrogène et d’azote résiduel.
Note 2 à l'article: L’endogaz est utilisé comme gaz de base ou gaz vecteur. La teneur en carbone (3.7.9) du matériau
ferreux est généralement d’environ 0,4 % en fraction massique. Si la teneur en carbone du matériau ferreux est plus
élevée, il est nécessaire d’ajouter un gaz producteur de carbone, par exemple, pour la cémentation.
3.1.22
atmosphère endothermique
atmosphère de four (3.1.31) produite endothermiquement et avec un potentiel en carbone susceptible d’être
ajusté à la teneur en carbone du matériau ferreux en cours de traitement thermique (3.1.35), de façon à
réduire, augmenter ou maintenir la teneur en carbone (3.7.9) à la surface du matériau ferreux
Note 1 à l'article: L’adjectif «endothermique» sous-entend qu’un transfert d’énergie thermique a lieu vers l’atmosphère.
3.1.23
égalisation
deuxième étape du chauffage (3.1.37) d’un matériau ferreux par laquelle la température requise a la surface
est atteinte dans toute sa section
Note 1 à l'article: (voir Figure 1)

Légende
X temps
Y température
1 courbe de chauffage en surface
2 courbe de chauffage à cœur
t temps de montée en température
t temps d’égalisation
t temps de chauffage
t temps de maintien à température
T température d’austénitisation ou de trempe
Figure 1 — Représentation schématique du chauffage lors d’un traitement d’austénitisation
3.1.24
diagramme d’équilibre
représentation graphique de la température et des limites de composition des aires des phases dans un
système allié
3.1.25
diamètre équivalent
diamètre équivalent de la vitesse de refroidissement
section déterminante
diamètre (d) d’un cylindre de même acier (de longueur ≥ 3d) dans lequel la vitesse de refroidissement (3.1.14)
à cœur est identique à la vitesse de refroidissement la plus lente relevée dans la pièce ferreuse considérée
ayant une forme irrégulière, pour le même mode de refroidissement (3.1.12)
[1]
Note 1 à l'article: La méthode de détermination du diamètre équivalent est décrite dans l’ISO 683-1 et l’ISO 683- 2.
3.1.26
transformation eutectoïde
transformation réversible de l’austénite (3.8.4) en perlite (3.8.26) (ferrite + cémentite) se produisant à
température constante
Note 1 à l'article: La température de transformation eutectoïde d’un fer pur est de 723 °C. Les éléments d’alliage et la
vitesse de refroidissement influent sur la température.

3.1.27
exogaz
mélange de gaz produit par combustion complète d’hydrocarbures
Note 1 à l'article: L’exogaz est généralement composé d’une fraction volumique de 6,8 % à 10 % de dioxyde de carbone,
2,4 % à 7,4 % de monoxyde de carbone, 2,5 % à 9,5 % d’hydrogène, de petites quantités d’oxygène, de la vapeur d’eau
et de l’azote résiduel.
Note 2 à l'article: L’exogaz est utilisé pour protéger les surfaces des matériaux ferreux de l’oxydation et a un effet de
décarburation.
3.1.28
atmosphère exothermique
atmosphère de four (3.1.31) produite exothermiquement et contrôlée sans oxydation du matériau ferreux
Note 1 à l'article: L’adjectif «exothermique» sous-entend qu’un transfert d’énergie thermique a lieu depuis l’atmosphère.
3.1.29
matériau ferreux
métaux et alliages dont l’élément principal est le fer
Note 1 à l'article: Les matériaux ferreux comprennent les produits et les pièces en acier et en fonte.
3.1.30
lit fluidisé
milieu de traitement thermique (3.1.35) obtenu avec de la poudre de céramique fluidisée par un gaz dans un
four chauffé à partir de l’extérieur
Note 1 à l'article: Le gaz de fluidisation peut être inerte pour protéger la surface des matériaux ferreux traités ou un
gaz réactif pour un traitement thermochimique (3.7.54) tel qu’une cémentation (3.7.13).
3.1.31
atmosphère de four
gaz contenus dans un four et utilisés pour un traitement thermique (3.1.35)
Note 1 à l'article: Les gaz contenus dans un four peuvent être des gaz purs ou un mélange gazeux. L’atmosphère peut
être inerte ou réactive.
Note 2 à l'article: L’objectif de l’atmosphère du four est de prévenir l’oxydation (3.9.11) ou la décarburation (3.9.2) ou
d’être l’agent ou un gaz réactif dans un traitement thermochimique (3.7.54).
3.1.32
conduction thermique
flux de chaleur spontané entre un corps à une température élevée et un corps à une température plus basse
et/ou à l’intérieur d’un matériau ferreux ayant des températures localement différentes, par exemple entre
la surface et à cœur
Note 1 à l'article: En l’absence de facteurs extérieurs, la différence de température se réduit au cours du temps, et les
corps approchent un état d’équilibre thermique.
3.1.33
convection thermique
transfert de chaleur d’un endroit à un autre par le mouvement de fluides
Note 1 à l'article: La convection est habituellement la forme de transfert de chaleur dominante dans les liquides et les
gaz.
Note 2 à l'article: La convection thermique au cours d’une trempe (3.3.19) peut être à phase unique (comme dans la
trempe par gaz (3.3.7)) ou double (comme dans la trempe à l’eau avec l’eau et le film de vapeur (3.3.28) simultanément).
En général, la convection à phase unique permet un échange de chaleur plus faible que la convection à double phase.

3.1.34
rayonnement thermique
rayonnement de chaleur
émission d’ondes électromagnétiques de tout matériau qui est à une température plus élevée que le zéro
absolu
Note 1 à l'article: Le rayonnement thermique constitue une conversion de l’énergie thermique en énergie
électromagnétique.
3.1.35
traitement thermique
succession d’opérations au cours desquelles un matériau ferreux (3.1.29) solide est soumis en tout ou partie
à des cycles thermiques (3.1.62) pour donner lieu à un changement de ses propriétés et/ou de sa structure
Note 1 à l'article: La composition chimique du matériau ferreux (3.1.29) peut être modifiée pendant ces opérations.
Voir traitement thermochimique (3.7.54).
3.1.36
cycle de traitement thermique
processus de traitement thermique complet impliquant le chauffage, le maintien à température et le
refroidissement
3.1.37
chauffage
augmentation de la température d’un matériau ferreux, de façon continue, discontinue ou progressive, en
une ou plusieurs phases
Note 1 à l'article: Il convient de préciser le milieu dans lequel le chauffage a lieu, par exemple sous atmosphère
protectrice, dans un gaz inerte ou noble, sous vide, dans l’air, etc.
3.1.38
conditions de chauffage
programme de chauffage
conditions (température, temps et mode de chauffage, etc.) dans lesquelles s’effectue le chauffage (3.1.37) du
matériau ferreux
3.1.39
loi de chauffage
courbe de chauffage
variation de la température en un point défini d’un matériau ferreux ou dans une charge de four, en fonction
du temps, au cours du chauffage (3.1.37)
Note 1 à l'article: La loi de chauffage peut être représentée sous la forme d’un graphique ou d’une formule mathématique.
3.1.40
vitesse de chauffage
variation de la température en fonction du temps au cours du chauffage (3.1.37)
Note 1 à l'article: Il faut distinguer la vitesse instantanée correspondant à une température spécifiée, de la vitesse
moyenne sur un intervalle de température ou de temps défini.
3.1.41
temps de chauffage
durée de chauffage
intervalle de temps séparant deux températures caractéristiques de la loi de chauffage (3.1.39)
Note 1 à l'article: II est toujours nécessaire de spécifier précisément quelles sont ces températures.
Note 2 à l'article: Le temps de chauffage correspond à la somme du temps de montée en température et du temps
d’égalisation.
3.1.42
temps de montée en température
temps nécessaire pour que la surface d’un matériau ferreux atteigne la température spécifiée au cours du
chauffage
3.1.43
traitement thermique par faisceau à haute énergie
traitement thermique utilisant différentes sources d’énergie à haute densité de puissance, telles qu'un laser,
un faisceau d’électrons ou du plasma, pour chauffer des matériaux ferreux
3.1.44
formage à chaud
formage des produits en acier dans une gamme de température généralement comprise entre 780 °C et
1 300 °C en fonction de la composition chimique de la pièce
Note 1 à l'article: Le formage à chaud comprend le laminage à chaud, le forgeage à chaud, le cintrage à chaud, etc.
Note 2 à l'article: Le formage entre les températures de formage à chaud et de formage à froid est appelé «warm
forming».
3.1.45
acier hypereutectoïde
acier contenant plus de carbone que la composition eutectoïde
3.1.46
acier hypoeutectoïde
acier contenant moins de carbone que la composition eutectoïde
3.1.47
diamètre critique de trempe idéal
diamètre d’un cylindre présentant au centre une structure de fraction volumique de 50 % de martensite
après un refroidissement dans les conditions idéales en matière d’indice de pouvoir de refroidissement (3.3.20)
3.1.48
chauffage par impulsions
mode de chauffage (3.1.37) permettant d’obtenir une élévation locale de température par de brefs apports
répétés d’énergie
Note 1 à l'article: Différentes sources d’énergie peuvent être utilisées, par exemple décharge de condensateur, lasers,
faisceaux d’électrons, etc.
3.1.49
traitement thermique par induction
traitement thermique utilisant l’induction électromagnétique pour générer des courants de Foucault à
l’intérieur d’un matériau ferreux afin de le chauffer
3.1.50
isoformage
procédé de traitement thermomécanique contrôlé (3.1.63) d’un acier consistant en une déformation plastique
réalisée durant la transformation de l’austénite (3.8.4) en perlite (3.8.26)
3.1.51
laminage de normalisation
procédé de laminage contrôlé (3.1.73) dans lequel la déformation finale est réalisée dans une certaine gamme
de température conduisant à des conditions du matériau équivalentes à celles obtenues après traitement de
normalisation (3.2.17), de sorte que les caractéristiques mécaniques spécifiées sont toujours atteintes dans
l’éventualité de toute normalisation ultérieure

3.1.52
traitement thermique par plasma
traitement thermique par bombardement ionique
traitement thermique par décharge luminescente
traitement thermique utilisant une décharge luminescente générée entre un matériau ferreux (faisant office
de cathode) et une anode dans une atmosphère spécifique dont la pression est inférieure à 0,1 MPa (en
−1 −3
général de 10 Pa à 10 Pa)
3.1.53
préchauffage
chauffage d’un matériau ferreux utilisant un ou plusieurs paliers de température et un temps de maintien à
température adapté jusqu’à ce que la température de traitement thermique soit atteinte
3.1.54
atmosphère protectrice
gaz protecteur
gaz destiné à éviter la modification de la composition de la couche superficielle de matériaux ferreux
pendant le traitement thermique (3.1.35), habituellement utilisé pour produire une atmosphère de four
(3.1.31) protectrice
Note 1 à l'article: Le gaz protecteur est généralement utilisé pour éviter l’oxydation (3.9.11) ou la décarburation (3.9.2).
Note 2 à l'article: La composition des gaz protecteurs dépend de l’objectif de leur utilisation.
Note 3 à l'article: La meilleure protection est obtenue dans des fours sous vide.
3.1.55
traitement de restauration
changement de la structure et des propriétés après le recuit (3.2.1) d’un matériau ferreux écroui, associé à
l’élimination des contraintes résiduelles et à la formation d’une région exempte de déformation
Note 1 à l'article: Le traitement de restauration est réalisé à une température inférieure à celle du traitement de
recristallisation (3.1.56).
Note 2 à l'article: Le traitement de restauration résulte des relèvements des dislocations et des glissements produits
par le mouvement des lacunes et des atomes.
3.1.56
traitement de recristallisation
changement de la structure et des propriétés après le recuit (3.2.1) d’un matériau ferreux écroui, associé à la
formation fréquente de nouveaux grains fins
Note 1 à l'article: Un grossissement de grain (3.8.17) peut se produire dans le matériau ferreux lorsque le degré de
déformation est critique.
Note 2 à l'article: Le traitement de recristallisation réduit généralement la résistance mécanique et accroît la ductilité.
3.1.57
maintien à température
portion du cycle thermique (3.1.62) au cours de laquelle la température est maintenue constante
Note 1 à l'article: II est nécessaire de préciser si la température est celle de la surface du matériau ferreux, celle à cœur
ou en tout autre point particulier sur le matériau ferreux ou dans la charge du four.
3.1.58
fonte à graphite sphéroïdal
fonte (3.1.5) contenant du graphite sphéroïdal
Note 1 à l'article: Elle diffère de la fonte grise à lamelles de graphite par sa composition chimique, simplement du fait
de l’addition de magnésium (de 0,04 % à 0,06 %), de cérium et d’autres terres rares qui influent sur la formation de
sphères de graphite.
Note 2 à l'article: Généralement, les fontes à nodules vont subir un traitement thermique, par exemple trempe étagée
bainitique (3.3.3), normalisation (3.2.17) trempe et revenu (3.4.8).
3.1.59
stabilisation de l’austénite résiduelle
phénomène qui réduit ou supprime les possibilités de transformation de l’austénite résiduelle (3.8.31) en
martensite (3.8.22) au cours d’un refroidissement (3.1.11) à une température inférieure à la température
ambiante
Note 1 à l'article: Cette stabilisation apparaît au cours d’un revenu effectué à basse température ou au cours d’un
maintien à la température ambiante après trempe (3.3.19).
3.1.60
traitement de stabilisation
traitement thermique (3.1.35) d’un matériau ferreux destiné à éviter des variations ultérieures de sa
géométrie, de ses dimensions, de sa microstructure et de ses propriétés au fil du temps
Note 1 à l'article: En général, le traitement de stabilisation peut lui-même entraîner des modifications qui pourront ne
pas être souhaitables par la suite.
3.1.61
acier
matériau ferreux dont l’élément principal est le fer et dont la teneur en carbone n’est pas supérieure à 2 % en
fraction massique
Note 1 à l'article: La présence de fortes teneurs en éléments carburigènes peut modifier la limite supérieure de la
teneur en carbone.
Note 2 à l'article: La désignation des aciers non alliés aptes au traitement thermique (3.1.35) et des aciers alliés est
[3] [4]
définie par l’ISO 4948-1 et l’ISO 4948-2 .
3.1.62
cycle thermique
évolution de la température en fonction du temps au cours d’un traitement thermique (3.1.35)
3.1.63
procédé de traitement thermomécanique contrôlé
TMCP
procédé de formage à chaud (3.1.44) dans lequel la déformation finale est réalisée dans une certaine gamme
de température, suivie d’un refroidissement à l’air ou d’un refroidissement accéléré
Note 1 à l'article: Ce traitement conduit à un matériau possédant certaines propriétés qui ne peuvent être obtenues
ou reproduites par un traitement thermique (3.1.35) seul. Le procédé de traitement thermomécanique contrôlé peut
comprendre un revenu (3.4.8) incluant un auto-revenu (3.4.1) mais excluant une trempe directe (3.3.5), une trempe et
un revenu (3.4.8).
Note 2 à l'article: Le procédé de traitement thermomécanique contrôlé a pour objectif de produire une structure à
grains fins, dure et à haute résistance qui ne peut pas être obtenue ou reproduite par un traitement thermique (3.1.35)
seul, et d’améliorer les aptitudes au soudage et au formage d’un produit en acier.
3.1.64
laminage thermomécanique
TMR
procédé de laminage dans lequel la déformation finale est effectuée dans une certaine gamme de
température conduisant à un matériau dans un état présentant certaines caractéristiques qui ne peuvent
pas être obtenues ou reproduites par un traitement thermique seul
Note 1 à l'article: Un chauffage ultérieur au-delà de 580 °C peut réduire les valeurs de résistance. Si une température
supérieure à 580 °C est nécessaire, il convient d'en informer le fournisseur.
Note 2 à l'article: Le laminage thermomécanique conduisant à l'état de livraison TMCP peut inclure des procédés à
vitesse de refroidissement accélérée, avec ou sans revenu (3.4.8), y compris auto-revenu (3.4.1), mais à l'exclusion de la
trempe directe et de la trempe suivie d'un revenu.

Note 3 à l'article: Dans certaines publications, le laminage thermomécanique est également considéré comme un
procédé de traitement thermomécanique contrôlé.
3.1.65
traitement thermomécanique
traitement mixte combinant déformation plastique et traitement thermique pour améliorer les propriétés
mécaniques d’un matériau ferreux
Note 1 à l'article: Le traitement thermomécanique comprend le formage à chaud (3.1.44), le laminage contrôlé (3.1.10),
etc.
3.1.66
chauffage à cœur
mode de chauffage qui permet à l’ensemble de la pièce d’atteindre une température uniforme
3.1.67
diagramme de transformation
représentation de la transformation de l’austénite (3.8.4) de matériaux ferreux en fonction du temps et de la
température pour une composition d’acier donnée
Note 1 à l'article: Un jeu de courbes peut être représenté dans une échelle semi-logarithmique en fonction du temps
en coordonnées logarithmiques qui définissent, pour chaque niveau de température, la transformation de phase de
l’austénite au début et la transformation en d’autres phases (3.8.27) à la fin.
Note 2 à l'article: À la fin de la transformation, les pourcentages des constituants de la microstructure et la dureté
peuvent être déterminés.
Note 3 à l'article: Il faut distinguer les diagrammes de transformation en lien avec la période de chauffage et de
maintien à température, appelés diagrammes des temps et températures d’austénitisation (diagrammes TTA) (3.1.67.1)
et les diagrammes en lien avec la période de refroidissement, appelés diagrammes de transformation isotherme
(diagramme TTT) (3.1.67.4).
3.1.67.1
diagramme des temps et températures d’austénitisation
diagramme TTA
diagramme représentant l’austénitisation de la structure initiale d’un matériau ferreux en fonction du temps
et de la température pour une composition donnée de l’acier et une microstructure initiale
Note 1 à l'article: Il faut distinguer les diagrammes d’austénitisation isotherme (3.1.67.2) des diagramme des temps et
températures d’austénitisation.
Note 2 à l'article: Un jeu de courbes peut être représenté dans une échelle semi-logarithmique en fonction du temps/de
la température en coordonnées logarithmiques qui définissent, pour chaque niveau de température, la transformation
de phase de la ferrite (3.8.11), de la perlite (3.8.26) et des carbures au début et la transformation en austénite (3.8.4) à
la fin.
3.1.67.2
diagramme d’austénitisation isotherme
diagramme IA
diagramme représentant des transformations d’une microstructure initiale en austénite à une température
donnée en fonction du temps
Note 1 à l'article: Pour une température donnée, le graphique se lit de gauche à droite en suivant la ligne de température
horizontale pour déterminer le temps requis pour la transformation de chaque composant de la microstructure au
début et la microstructure austénitique obtenue à la fin.
Note 2 à l'article: Les différences dans la microstructure initiale peuvent modifier le diagramme.

3.1.67.3
diagramme d’austénitisation continu
diagramme représentant des transformations d’une microstructure initiale en austénite à une vitesse de
chauffage donnée en fonction du temps
Note 1 à l'article: Un jeu de courbes pour différentes vitesses de chauffage peut être représenté dans une échelle semi-
logarithmique en fonction du temps/de la température en coordonnées logarithmiques.
Note 2 à l'article: Pour une vitesse de chauffage donnée sur la courbe, le temps et la température au début et à la fin du
changement de chaque composant de la structure initiale et de la structure austénitique peuvent être obtenus.
Note 3 à l'article: Les différences dans la microstructure initiale peuvent modifier le diagramme.
3.1.67.4
diagramme des temps et températures de transformation
diagramme TTT
diagramme de transformation isotherme
diagramme IT
diagramme représentant des transformations isothermes de l’austénite métastable (3.8.39)
Note 1 à l'article: Les diagrammes TTT peuvent être utilisés pour déterminer la fraction volumique de chaque phase
(3.8.27) et sa dureté après la transformation.
3.1.67.5
diagramme de transformation en refroidissement continu
diagramme CCT
diagramme représentant des transformations de l’austénite (3.8.4) dans des conditions de refroidissement
continu
Note 1 à l'article: Sur la ligne correspondante à 500 °C, le paramètre de refroidissement λ, qui correspond au temps
mis pour passer de 800 °C à 500 °C en secondes divisé par 100 ou directement en secondes, peut être déterminé.
3.1.68
point de transformation
température de transformation d’une microstructure à une autre
Note 1 à l'article: Le terme doit être complété par une indication du type de la microstructure, par exemple point de
transformation de l’étape martensitique, de l’étape perlitique, etc.
3.1.69
intervalle critique
intervalle de température à l’intérieur duquel un produit ferreux subit un changement de phase (3.8.27)
3.1.70
température de transformation
point critique
température à laquelle se produit un changement de phase (3.8.27) et, par extension, température à
laquelle commence ou s’achève une telle transformation lorsque cette dernière s’étage sur un intervalle de
températures
Note 1 à l'article: Pour les aciers, les principales températures de transformation suivantes peuvent être distinguées:
— A , température d’équilibre définissant la limite inférieure d’existence de l’austénite (3.8.4);
— A , température d’équilibre définissant la limite supérieure d’existence de la ferrite (3.8.11);
— A , température d’équilibre définissant la limite supérieure d’existence de la cémentite (3.8.8) dans un acier
cm
hypereutectoïde (3.1.45);
— M , température à laquelle l’austénite commence à se transformer en martensite (3.8.22) au cours du refroidissement;
s
— M , température à laquelle s’achève la transformation pratiquement totale de l’austénite en martensite au cours du
f
refroidissement;
— M , température à laquelle une fraction volumique de x % d’austénite sont transformés en martensite au cours du
x
refroidissement.
3.1.71
refroidissement ultra-rapide
mode de refroidissement principalement réalisé au cours du procédé de trempe des plaques minces, dans le
but d’affiner la microstructure de l’acier et d’améliorer les propriétés mécaniques par un refroidissement à
l’eau sous haute pression à une vitesse nettement supérieure à celle du refroidissement à l’eau
3.1.72
traitement sous vide
traitement thermique réalisé dans un environnement sous vide à une pression inférieure à 0,1 MPa
−1 −3
Note 1 à l'article: La pression est en général de 1 × 10 Pa - 1 × 10 Pa)
3.1.73
écrouissage
renforcement d’un matériau ferreux par déformation
Note 1 à l'article: Ce renforcement apparaît à la suite de mouvements des dislocations et de la génération de dislocations
dans la structure cristalline du matériau ferreux.
Note 2 à l'article: Une structure écrouie peut être éliminée par recristallisation.
3.2 Termes relatifs au recuit et à la normalisation
3.2.1
recuit
traitement thermique (3.1.35) comportant un chauffage (3.1.37) et un maintien à température (3.1.57)
appropriée, suivis d’un refroidissement (3.1.11) réalisé dans des conditions telles, qu’après retour à la
température ambiante, le matériau ferreux soit dans un état structural plus proche de l’état d’équilibre
Note 1 à l'article: Cette définition étant très générale, il est recommandé d’utiliser une formulation précisant le but
du traitement. Voir par exemple recuit blanc (3.2.4), recuit complet (3.2.8), recuit d’adoucissement (3.2.21), recuit
intercritique (3.2.13), recuit isotherme (3.2.14) et recuit subcritique.
3.2.2
bainitisation
austénitisation (3.1.2) et trempe (3.3.19) jusqu’à une température au-dessus de Ms et maintien à température
isotherme pour assurer la transformation de l’austénite (3.8.4) en bainite (3.8.5) haute ou basse
Note 1 à l'article: La bainitisation peut entraîner la formation de bainites haute et basse, alors que la trempe étagée
bainitique engendre généralement de la bainite basse.
3.2.3
déshydrogénation
recuit de déshydrogénation
recuit (3.2.1) à une température inférieure à A pendant une certain temps de mise à température permettant
la libération de l’hydrogène absorbé dans un matériau ferreux sans modifier sa structure
Note 1 à l'article: Le temps de mise à température dépend de la taille du matériau ferreux et de la teneur en hydrogène.
Note 2 à l'article: Pour les aciers durcis par trempe ou cémentés, l’hydrogène est habituellement éliminé à une
température de revenu comprise entre 230 °C et 300 °C, avec quelques heures de maint
...