EN ISO 4885:2026
(Main)Ferrous materials - Heat treatments - Vocabulary (ISO 4885:2026)
General Information
- Abstract
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.
- Status
- Published
- Publication Date
- 04-Aug-2026
- Technical Committee
- ECISS/TC 100 - General issues
- Drafting Committee
- ECISS/TC 100/WG 1 - Vocabulary
- Current Stage
- 6060 - Definitive text made available (DAV) - Publishing
- Start Date
- 05-Aug-2026
- Completion Date
- 05-Aug-2026
Overview
EN ISO 4885:2026 - Ferrous Materials – Heat Treatments – Vocabulary is an international standard developed by CEN, aligning with ISO 4885:2026. This document provides comprehensive definitions for key terms used in the heat treatment of ferrous materials, including steels and cast irons. It promotes a unified technical language essential for communication within the metallurgy and heat treatment industries worldwide.
The standard encompasses terminology related to all main processes, treatment methods, structures, and phenomena observed in heat-treated ferrous materials. Additionally, Annex A offers an alphabetical list of defined terms, accompanied by their equivalents in French, German, Russian, Chinese, and Japanese, supporting international exchange and harmonization.
Key Topics
The vocabulary defined in EN ISO 4885:2026 covers a broad scope including:
- General heat treatment terms: Definitions for fundamental processes such as heating, cooling, soaking, and thermal cycling.
- Process-specific terminology: Vocabulary for annealing, normalizing, quenching, tempering, ageing, and thermochemical treatments.
- Cooling and heating methods: Terms like accelerated cooling, controlled rolling, vacuum heat treatment, and high energy beam heat treatment.
- Structural and phase transformations: Descriptions of microstructural changes such as austenitizing, martensite formation, bainite transformation, and eutectoid reactions.
- Atmospheric conditions: Definitions for controlled atmospheres, furnace atmospheres, protective atmospheres, and related gas mixtures (e.g., endogas, exogas).
- Characteristics and measurement: Key terms for cooling rates, critical diameters, equilibrium diagrams, and transformation diagrams (including TTT, CCT, and TTA diagrams).
- Defect terminology: Identifies and names typical defects that may arise in heat treated ferrous materials.
Table 1 in the standard provides a valuable overview of the various iron-carbon (Fe-C) phase relationships, essential for understanding the effects of heat treatment conditions.
Applications
EN ISO 4885:2026 is a critical reference for:
- Metallurgical and heat treatment industry professionals: Ensures precise use and understanding of technical terminology in manufacturing processes, quality control, and research.
- Technical documentation and standardization: Facilitates the creation of specifications, procedures, quality manuals, and safety instructions that require unambiguous communication.
- International trade and cross-border projects: Reduces misinterpretation of terms in specifications and contractual documents by providing multilingual equivalents and globally recognized definitions.
- Education and training: Assists instructors and learners in metallurgy, material science, and engineering programs by standardizing the vocabulary related to heat treatment.
- Regulatory and compliance documentation: Supports conformance with national and international requirements by aligning with globally accepted terms.
Related Standards
Organizations adopting EN ISO 4885:2026 should also be aware of these relevant international standards:
- ISO 18203: Steel - Determination of the thickness of surface-hardened layers.
- ISO 4948-1, ISO 4948-2: Classification of unalloyed and alloyed steels for nomenclature and designation.
- Other standards within the 25.200 (Heat Treatment) and 77.140.01 (Iron and Steel Products) ICS groups: These provide further technical details for processes and product requirements.
Practical Value
Adopting EN ISO 4885:2026 ensures standardized communication regarding heat treatment of ferrous materials, which:
- Reduces the risk of errors in interpreting processing instructions or quality requirements.
- Streamlines procurement, quality assurance, and manufacturing documentation across international supply chains.
- Enhances efficiency in training, technical writing, and regulatory compliance.
- Supports fair and transparent trade of iron and steel products by providing a clear, harmonized vocabulary.
For professionals and organizations involved in the field of ferrous metallurgy, EN ISO 4885:2026 establishes a foundational language to support innovation, quality, and global collaboration in heat treatment processes.
Relations
- Effective Date
- 06-Sep-2023
- Effective Date
- 12-Aug-2026
- Effective Date
- 12-Aug-2026
- Effective Date
- 12-Aug-2026
- Effective Date
- 12-Aug-2026
- Referred By
EN 10132:2021 - Cold rolled narrow steel strip for heat treatment - Technical delivery conditions - Effective Date
- 12-Aug-2026
- Effective Date
- 12-Aug-2026
- Referred By
CEN ISO/TR 14745:2015 - Welding - Post-weld heat treatment parameters for steels (ISO/TR 14745:2015) - Effective Date
- 12-Aug-2026
- Effective Date
- 12-Aug-2026
- Effective Date
- 12-Aug-2026
- Effective Date
- 12-Aug-2026
- Effective Date
- 12-Aug-2026
- Effective Date
- 12-Aug-2026
- Effective Date
- 12-Aug-2026
- Effective Date
- 12-Aug-2026
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Frequently Asked Questions
EN ISO 4885:2026 is a standard published by the European Committee for Standardization (CEN). Its full title is "Ferrous materials - Heat treatments - Vocabulary (ISO 4885:2026)". This standard covers: 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.
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.
EN ISO 4885:2026 is classified under the following ICS (International Classification for Standards) categories: 01.040.25 - Manufacturing engineering (Vocabularies); 01.040.77 - Metallurgy (Vocabularies); 25.200 - Heat treatment; 77.140.01 - Iron and steel products in general. The ICS classification helps identify the subject area and facilitates finding related standards.
EN ISO 4885:2026 has the following relationships with other standards: It is inter standard links to EN ISO 4885:2018, EN 10225-3:2019+A1:2023, EN 10216-1:2002, EN 10225-3:2019, EN 10217-2:2002, EN 10132:2021, EN 10216-2:2002+A2:2007, CEN ISO/TR 14745:2015, EN 10085:2001, EN 10263-1:2017, EN 10277:2018, EN 10217-6:2002, EN 10216-5:2013, EN 4632-003:2010, EN 10270-1:2011+A1:2017. Understanding these relationships helps ensure you are using the most current and applicable version of the standard.
EN ISO 4885:2026 is available in PDF format for immediate download after purchase. The document can be added to your cart and obtained through the secure checkout process. Digital delivery ensures instant access to the complete standard document.
Standards Content (Sample)
SLOVENSKI STANDARD
01-oktober-2026
Železove zlitine - Toplotna obdelava - Slovar (ISO 4885:2026)
Ferrous materials - Heat treatments - Vocabulary (ISO 4885:2026)
Eisenwerkstoffe - Wärmebehandlung - Begriffe (ISO 4885:2026)
Matériaux ferreux - Traitements thermiques - Vocabulaire (ISO 4885:2026)
Ta slovenski standard je istoveten z: EN ISO 4885:2026
ICS:
01.040.77 Metalurgija (Slovarji) Metallurgy (Vocabularies)
25.200 Toplotna obdelava Heat treatment
77.140.01 Železni in jekleni izdelki na Iron and steel products in
splošno general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EN ISO 4885
EUROPEAN STANDARD
NORME EUROPÉENNE
August 2026
EUROPÄISCHE NORM
ICS 01.040.25; 01.040.77; 25.200; 77.140.01 Supersedes EN ISO 4885:2018
English Version
Ferrous materials - Heat treatments - Vocabulary (ISO
4885:2026)
Matériaux ferreux - Traitements thermiques - Eisenwerkstoffe - Wärmebehandlung - Begriffe (ISO
Vocabulaire (ISO 4885:2026) 4885:2026)
This European Standard was approved by CEN on 25 July 2026.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2026 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 4885:2026 E
worldwide for CEN national Members.
Contents Page
European foreword . 3
European foreword
This document (EN ISO 4885:2026) has been prepared by Technical Committee ISO/TC 17 "Steel" in
collaboration with Technical Committee CEN/TC 459/SC 12 “General issues” the secretariat of which is
held by BSI.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by February 2027, and conflicting national standards
shall be withdrawn at the latest by February 2027.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 4885:2018.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 4885:2026 has been approved by CEN as EN ISO 4885:2026 without any modification.
International
Standard
ISO 4885
Fourth edition
Ferrous materials — Heat
2026-07
treatments — Vocabulary
Matériaux ferreux — Traitements thermiques — Vocabulaire
Reference number
ISO 4885:2026(en) © ISO 2026
ISO 4885:2026(en)
© ISO 2026
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
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Email: copyright@iso.org
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Published in Switzerland
ii
ISO 4885:2026(en)
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
ISO 4885:2026(en)
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.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
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
International Standard ISO 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)
ISO 4885:2026(en)
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,
carburization or decarburization
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 prevent oxidation and decarburization, or allow
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
(3.3.21).
ISO 4885:2026(en)
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.
ISO 4885:2026(en)
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
ISO 4885:2026(en)
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.
ISO 4885:2026(en)
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 (3.3.21) can be single phase [as in gas quenching (3.3.7)] or dual
phase [as in water quenching with water and vapor film (3.3.29) 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.
ISO 4885:2026(en)
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 (3.3.22)
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
ISO 4885:2026(en)
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
andtempering (3.4.3).
ISO 4885:2026(en)
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 (3.3.21).
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
(3.4.7) 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 (3.4.7) but excluding direct
quenching and quenching and tempering.
Note 3 to entry: In some publications, TMR is also considered as a process of TMCP.
ISO 4885:2026(en)
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.
ISO 4885:2026(en)
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.
ISO 4885:2026(en)
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 (3.3.21) 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.
ISO 4885:2026(en)
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 graphitiz
...