SIST EN ISO 4885:2018

Ferrous materials - Heat treatments - Vocabulary (ISO 4885:2018)

This document 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.

Eisenwerkstoffe - Wärmebehandlung - Begriffe (ISO 4885:2018)

Dieses Dokument legt die wichtigsten Begriffe für die Wärmebehandlung von Eisenwerkstoffen fest.
ANMERKUNG   Der Begriff „Eisenwerkstoffe“ umfasst Erzeugnisse und Werkstücke aus Stahl und Gusseisen.
Anhang A enthält eine alphabetische Auflistung der Begriffe, die in diesem Dokument definiert sind sowie ihre Entsprechungen in Französisch, Deutsch, Chinesisch und Japanisch.
Tabelle 1 zeigt die verschiedenen Eisen Kohlenstoff (Fe-C)-Phasen.

Matériaux ferreux - Traitements thermiques - Vocabulaire (ISO 4885:2018)

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).

Železove zlitine - Toplotna obdelava - Slovar (ISO 4885:2018)

Ta dokument določa pomembne izraze, ki se uporabljajo pri toplotni obdelavi železovih materialov.
OPOMBA: Izraz »železovi materiali« vključuje proizvode in obdelovance iz jekla in litega železa.
V dodatku A so po abecednem redu navedeni izrazi, opredeljeni v tem dokumentu, ter njihove francoske, nemške, kitajske in japonske ustreznice.
V preglednici 1 so prikazane različne faze železovega karbonata (Fe-C).

General Information

• Status: Published
• Public Enquiry End Date: 23-Jan-2018
• Publication Date: 18-Apr-2018
• ICS: 01.040.77 - Metallurgy (Vocabularies)
• ICS: 25.200 - Heat treatment
• ICS: 77.080.01 - Ferrous metals in general
• Technical Committee: IFEK - Ferrous metals
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 12-Apr-2018
• Due Date: 17-Jun-2018
• Completion Date: 19-Apr-2018
• Ref Project: EN ISO 4885:2018 - Ferrous materials - Heat treatments - Vocabulary (ISO 4885:2018)

Relations

• Replaces: SIST EN ISO 4885:2017 - Ferrous products - Heat treatments - Vocabulary (ISO 4885:2017)
• Effective Date: 11-Apr-2018
• Replaces: SIST EN ISO 4885:2017 - Ferrous products - Heat treatments - Vocabulary (ISO 4885:2017)
• Effective Date: 08-Jun-2022

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN ISO 4885:2018
01-junij-2018
1DGRPHãþD
SIST EN ISO 4885:2017
Železove zlitine - Toplotna obdelava - Slovar (ISO 4885:2018)
Ferrous materials - Heat treatments - Vocabulary (ISO 4885:2018)
Matériaux ferreux - Traitements thermiques - Vocabulaire (ISO 4885:2018)
Ta slovenski standard je istoveten z: EN ISO 4885:2018
ICS:
01.040.77 Metalurgija (Slovarji) Metallurgy (Vocabularies)
25.200 Toplotna obdelava Heat treatment
77.080.01 Železne kovine na splošno Ferrous metals in general
SIST EN ISO 4885:2018 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 4885:2018
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SIST EN ISO 4885:2018
EN ISO 4885
EUROPEAN STANDARD
NORME EUROPÉENNE
April 2018
EUROPÄISCHE NORM
ICS 01.040.25; 01.040.77; 25.200; 77.140.01 Supersedes EN ISO 4885:2017
English Version
Ferrous materials - Heat treatments - Vocabulary (ISO
4885:2018)

Matériaux ferreux - Traitements thermiques - Eisenwerkstoffe - Wärmebehandlung - Begriffe (ISO

Vocabulaire (ISO 4885:2018) 4885:2018)
This European Standard was approved by CEN on 2 April 2018.

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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,

Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey 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

© 2018 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 4885:2018 E

worldwide for CEN national Members.
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SIST EN ISO 4885:2018
EN ISO 4885:2018 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

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SIST EN ISO 4885:2018
EN ISO 4885:2018 (E)
European foreword

This document (EN ISO 4885:2018) has been prepared by Technical Committee ISO/TC 17 "Steel" in

collaboration with Technical Committee ECISS/TC 100 “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 October 2018, and conflicting national standards shall

be withdrawn at the latest by October 2018.

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 4885:2017.

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, Former Yugoslav Republic of Macedonia,

France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,

Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and the United Kingdom.
Endorsement notice

The text of ISO 4885:2018 has been approved by CEN as EN ISO 4885:2018 without any modification.

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SIST EN ISO 4885:2018
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SIST EN ISO 4885:2018
INTERNATIONAL ISO
STANDARD 4885
Third edition
2018-02
Ferrous materials — Heat treatments
— Vocabulary
Matériaux ferreux — Traitements thermiques — Vocabulaire
Reference number
ISO 4885:2018(E)
ISO 2018
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SIST EN ISO 4885:2018
ISO 4885:2018(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2018

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
CP 401 • Ch. de Blandonnet 8
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Tel. [phone]
Fax [phone]
[e-mail]
www.iso.org
Published in Switzerland
ii © ISO 2018 – All rights reserved
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SIST EN ISO 4885:2018
ISO 4885:2018(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

Annex A (informative) Equivalent terms .......................................................................................................................................................31

Bibliography .............................................................................................................................................................................................................................41

© ISO 2018 – All rights reserved iii
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SIST EN ISO 4885:2018
ISO 4885:2018(E)
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 documents 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).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation on 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 the following

URL: www .iso .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 17, Steel.

This third edition cancels and replaces the second edition (ISO 4885:2017), of which it constitutes a

minor revision with a corrected Figure 1 d).
iv © ISO 2018 – All rights reserved
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SIST EN ISO 4885:2018
INTERNATIONAL STANDARD ISO 4885:2018(E)
Ferrous materials — Heat treatments — Vocabulary
1 Scope

This document 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.
2 Normative references
There are no normative references in this document.
3 Terms and definitions

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at https:// www .iso .org/ obp
3.1
acicular structure
structure which appears in the form of needles in a micrograph
3.2
activity

effective concentration of species under non-ideal (e.g. concentrated) conditions; for heat treatment

(3.108), this means the effective concentration of carbon or nitrogen (or both) in heat treatment media

and in ferrous materials

Note 1 to entry: Ratio of the vapour pressure of a gas (usually carbon or nitrogen) in a given state (e.g. in austenite

(3.12) of specific carbon/nitrogen concentration) to the vapour pressure of the pure gas, as a reference state, at

the same temperature.
3.3
ageing

change in the properties of steels depending on time and temperature after hot working or heat

treatment (3.108) or after cold-working operation, due to the migration of interstitial elements

Note 1 to entry: The ageing phenomenon can lead to higher strength and lower ductility.

Note 2 to entry: The ageing effect can be accelerated either by cold forming and/or subsequent heating (3.109) to

moderate temperatures (e.g. 250 °C) and soaking (e.g. for 1 h).
3.4
air-hardening steel
DEPRECATED: self-hardening steel

steel, the hardenability (3.103) of which is such that cooling (3.45) in air produces a martensitic structure

in objects of considerable size
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SIST EN ISO 4885:2018
ISO 4885:2018(E)
3.5
alpha iron
stable state of pure iron at temperatures below 911 °C

Note 1 to entry: The crystalline structure of an alpha iron is body-centred cubic.

Note 2 to entry: Alpha iron is ferromagnetic at temperatures below 768 °C (the Curie point).

3.6
alpha mixed crystal

iron with body-centred cubic lattice structure with alloying elements in interstitial or substitutional

solution
Note 1 to entry: The material science for alpha mixed crystal is ferritic.
Note 2 to entry: Alpha mixed crystal is ferromagnetic.
3.7
aluminizing
DEPRECATED: calorizing
surface treatment into and on a workpiece (3.201) relating to aluminium
3.8
annealing

heat treatment (3.108) consisting of heating (3.109) and soaking (3.185) at a suitable temperature

followed by cooling (3.45) under conditions such that, after return to ambient temperature, the metal

will be in a structural 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 bright annealing (3.29), full annealing (3.89), softening/soft annealing (3.186), inter-critical

annealing (3.122), isothermal annealing (3.127) and subcritical annealing.
3.9
ausferrite

fine-grained mixture of ferrite (3.85) and stabilized austenite (3.12) which should lead to high hardness

and ductility of austempered ductile cast iron (ADI)
3.10
ausforming

thermomechanical treatment (3.208) of a workpiece which consists of plastically deforming the

metastable austenite (3.12) before subjecting it to the martensitic and/or bainitic transformation

3.11
austempering

isothermal heat treatment for producing bainitic (see 3.17 and 3.18) or ausferritic (see 3.9) structure of

a workpiece

Note 1 to entry: The final cooling (3.45) to ambient temperature is not at a specific rate.

3.12
austenite
solid solution of one or more elements in gamma iron (3.91)
Note 1 to entry: See also Table 1.
3.13
austenitic steel
steel where the structure consists of austenite (3.12) at ambient temperature

Note 1 to entry: Cast austenitic steels can contain up to about 20 % of ferrite (3.85).

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SIST EN ISO 4885:2018
ISO 4885:2018(E)
3.14
austenitizing

heating (3.109) a workpiece to austenitizing temperature (3.15) and holding at this, so that the

microstructure is predominantly austenitic (3.12)

Note 1 to entry: The minimum temperature required depends on the speed of heating and the steel composition.

The length of the hold period will depend on the heating conditions used.
3.15
austenitizing temperature
temperature at which the workpiece is maintained during austenitization (3.14)
3.16
auto-tempering
self-tempering

tempering (3.203) undergone by martensite (3.137) during quenching (3.168) or subsequent cooling (3.45)

3.17
bainite

microstructure resulting from the transformation of austenite (3.12) at temperatures above martensite

(3.137) start temperature (M ) and outside the pearlite (3.155) range consisting of ferrite laths and

carbides which are dispersed either inside the ferrite laths (lower bainite) or between the ferrite laths

(upper bainite)
Note 1 to entry: See also Table 1.
3.18
bainitizing

austenitizing (3.14) and quenching (3.168) to a temperature above M and isothermal soaking to ensure

a transformation of the austenite (3.12) to bainite (3.17)
3.19
bake hardening steel

steel with the ability to gain an increase of yield strength after a plastic pre-strain and a subsequent

heat treatment (3.108) in the usual industrial paint processes (in the region of 170 °C for 20 min)

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) and a good dent resistance.

3.20
baking

heat treatment (3.108) permitting the release of hydrogen absorbed in a ferrous product without

modifying its structure

Note 1 to entry: The treatment is generally carried out following electrolytic plating or pickling, or a welding

operation.
3.21
banded structure

lines of constituents in the microstructure caused by segregation (3.179) during solidification

3.22
blacking

operation carried out in an oxidizing medium at a temperature such that the polished surface of a

workpiece becomes covered with a thin, continuous, adherent film of dark-coloured oxide (see 3.151)

3.23
black nitriding
nitriding (3.143) followed by oxidation (3.150) of the steel surface

Note 1 to entry: After nitrocarburizing (3.144), blacking (3.22) will improve the corrosion resistance and the

surface properties.
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SIST EN ISO 4885:2018
ISO 4885:2018(E)
3.24
blank nitriding
blank nitrocarburizing

simulation treatment which consists of reproducing the thermal cycle of nitriding (3.143)/

nitrocarburizing (3.144) without the nitriding/nitrocarburizing medium

Note 1 to entry: This treatment makes it possible to assess the metallurgical consequences of the thermal cycle of

nitriding/nitrocarburizing.
3.25
batch annealing
box annealing

process in which strip is annealed in tight coil form, within a protective atmosphere, for a predetermined

time-temperature cycle
3.26
blueing

treatment carried out in an oxidizing medium (see 3.152) at a temperature such that the bright surface

of a workpiece becomes covered with a thin, continuous, adherent film of blue-coloured oxide

Note 1 to entry: If the blueing is carried out in superheated water vapour, it is also called steam treatment.

3.27
boost-diffuse carburizing

carburizing (3.36) carried out in two or more successive stages and/or different temperatures with

different carbon potentials
3.28
boriding

thermochemical treatment (3.207) of a workpiece to enrich the surface of a workpiece with boron

Note 1 to entry: The medium in which boriding takes place should be specified, e.g. pack boriding, paste

boriding, etc.
3.29
bright annealing

annealing (3.8) in a medium preventing the oxidation (3.150) of the surface and keeps the original

surface quality
3.30
burning

irreversible change in the structure and properties brought about by the onset of melting at the grain

boundaries and surface
3.31
carbon activity

effective concentration of carbon under non-ideal (e.g. concentrated) conditions; for heat treatment

(3.108), this means the effective concentration of carbon in heat treatment media and in ferrous

materials
3.32
carbon mass transfer coefficient

coefficient of the mass of carbon transfer from the carburizing medium into steel (per unit surface area

and time)

Note 1 to entry: Also defined as the mass of carbon transferred from the carburizing medium into the steel,

per unit surface area per second, for a unit difference between the carbon potential and actual surface carbon

content.
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SIST EN ISO 4885:2018
ISO 4885:2018(E)
3.33
carbon level

carbon content in percent of mass in an austenitized probe of pure iron at a given temperature in the

equilibrium with the carburizing medium

Note 1 to entry: The “carbon level” has been defined for practical use, because the carbon potential of steels

cannot be measured directly in carburizing media; see Reference [13].
3.34
carbon profile
carbon content depending on the distance from the surface
3.35
carbonitriding

thermochemical treatment (3.207) to enrich the surface layer with carbon and nitrogen

Note 1 to entry: The elements are in solid solution in the austenite (3.12), usually the carbonitrided workpiece

undergoes quench hardening (3.167) (immediately or later).
Note 2 to entry: Carbonitriding is a carburizing (3.36) process.

Note 3 to entry: The medium in which carbonitriding takes place should be specified, e.g. gas, salt bath, etc.

3.36
carburizing
DEPRECATED: cementation

thermochemical treatment (3.207) which is applied to a workpiece in the austenitic state, to obtain a

surface enrichment in carbon, which is in solid solution in the austenite (3.12)

Note 1 to entry: The carburized workpiece undergoes quench hardening (3.167) (immediately or later).

Note 2 to entry: The medium in which carburizing takes place should be specified, e.g. gas, pack, etc.

3.37
case hardening

treatment consisting of carburizing (3.36) or carbonitriding (3.35) followed by quench hardening (3.167)

Note 1 to entry: See Figure 1.
a) Direct-hardening treatment
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SIST EN ISO 4885:2018
ISO 4885:2018(E)
b) Single-quench hardening treatment
c) Quench-hardening treatment with isothermal transformation
d) Double-quench hardening treatment
Key
1 carburizing, carbonitriding 6 cooling
2 quenching 7 quench-hardening treatment
3 tempering 8 isothermal transformation
4 Ac core 9 Ac surface after carburizing
3 3
5 Ac surface

Figure 1 — Schematic representation of the possible thermal cycles of various case-hardening

treatments
3.38
cast iron

alloy of iron, carbon and silicon where the carbon content is approximately more than 2 %

3.39
cementite
iron carbide with the formula Fe C
Note 1 to entry: See Table 1.
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SIST EN ISO 4885:2018
ISO 4885:2018(E)
Table 1 — Iron-carbon (Fe-C) phases
Phase Crystal structure Properties Typical hardness
Ferrite, α bcc soft, tough, magnetic 60 HBW to 90 HBW
Austenite, γ fcc fair strength, non-magnetic 150 HBW (1,5 % C)
Cementite, Fe C rombic hard, brittle chemical composition 820 HBW
Pearlite with coarse α + Fe C, lamellar combination of tough ferrite 200 HBW
lamellas (0,4 μm) and hard cementite
Pearlite with fine α + Fe C, lamellar harder than pearlite with 400 HBW
lamellas (0,1 μm) coarse lamellas
Spheroidite α + globular Fe C soft 120 HBW to 230 HBW,
depending on
carbon and alloy content
Upper bainite precipitations of properties such as pearlite with 400 HBW
Fe C on surface fine lamellas
of α
Lower bainite precipitations of strength near martensite, but 600 HBW
Fe C inside of α tougher than tempered martensite
Martensite, α’, bcc, slightly hard, brittle 250 HV to 950 HV,
non-tempered tetragonic depending on carbon
content
Martensite, α’, bcc, slightly softer and tougher than 250 HV to 650 HV,
tempered tetragonic non-tempered martensite depending on carbon
content and tempering
temperature
3.40
chromizing
surface treatment into and on a workpiece (3.201) relating to chromium

Note 1 to entry: The surface layer can consist of practically pure chromium (on low-carbon steels) or of chromium

carbide (on high-carbon steels).
3.41
compound layer
DEPRECATED: white layer

surface layer formed during thermochemical treatment (3.207) and made up of the chemical compounds

formed by the element(s) introduced during the treatment and certain elements from the base metal

EXAMPLE The surface layer may consist of the layer of nitrides formed during nitriding (3.143), the layer

of borides formed during boriding (3.28), the layer of chromium carbide formed during the chromizing (3.40) of

high-carbon steel.

Note 1 to entry: In English, the term “white layer” is improperly used to designate this layer on nitrided and

nitrocarburized ferrous products.
3.42
continuous annealing

process in which strip is annealed by moving continuously through an oven within a protective

atmosphere
3.43
continuous-cooling transformation diagram
CCT diagram
see 3.210.2
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SIST EN ISO 4885:2018
ISO 4885:2018(E)
3.44
controlled rolling

rolling process where rolling temperature and reduction are controlled to achieve enhanced mechanical

properties, e.g. normalizing rolling, thermomechanical rolling

Note 1 to entry: Controlled rolling is used for fine-grain ferritic steels (3.86) and for dual-phase steel for obtaining

fine-grain structure.
3.45
cooling

reduction of (or operation to reduce) the temperature of a hot workpiece, either continuous,

discontinuous, gradual or interrupted

Note 1 to entry: The medium in which cooling takes place should be specified, e.g. in furnace, air, oil, water. See

also quenching (3.168).
3.46
cooling condition

condition(s) (temperature and kind of cooling medium, relative movements, agitation, etc.) under which

the cooling (3.45) of the workpiece takes place
3.47
cooling function

reduction of the temperature as a function of time of a determined point of a workpiece

Note 1 to entry: This function could be shown as a graph or written in a mathematical form.

3.48
cooling rate
variation in temperature as a function of time during cooling (3.45)
Note 1 to entry: A distinction is made between
— an instantaneous rate corresponding to a specified temperature, and
— an average rate over a defined interval of temperature or time.
3.49
cooling time

interval of time separating two characteristic temperatures of the cooling function (3.47)

Note 1 to entry: It is always necessary to specify precisely what the temperatures are.

3.50
core refining

process to get a fine grain and a homogenous microstructure in the core, often done by hardening of

carburized workpieces
Note 1 to entry: See Figures 1 b), c) and d).
3.51
critical cooling course

cooling procedure 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

(3.48) in general or at given temperatures or times.
3.52
critical cooling rate
cooling rate (3.48) corresponding to the critical cooling course (3.51)
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SIST EN ISO 4885:2018
ISO 4885:2018(E)
3.53
critical diameter

diameter (d) of a cylinder with a length ≥3 d, having a structure of 50 % by volume of martensite (3.137)

after quench hardening (3.167) with defined conditions at its centre
3.54
decarburization
depletion of carbon from the surface layer of a workpiece

Note 1 to entry: This depletion can be either partial (partial decarburization) or nominally complete (complete

decarburization). The sum of the two types of decarburization (partial and complete) is termed total

decarburization; see ISO 3887.
3.55
decarburizing

thermochemical treatment (3.207) intended to produce decarburization (3.54) of a workpiece

3.56
decomposition of austenite
austenite transformation

decomposition into ferrite (3.85) and pearlite (3.155) or ferrite and cementite (3.39) with decreasing

temperature
3.57
delta iron
stable state of pure iron between 1 392 °C and its melting point

Note 1 to entry: The crystalline structure of a delta iron is body-centred cubic, identical to that of the alpha

iron (3.5).
Note 2 to entry: Delta iron is paramagnetic.
3.58
depth of carburizing
carburizing depth

distance between the surface of a workpiece and a specified limit characterizing the thickness of the

layer enriched in carbon, which means effective case depth
3.59
depth of decarburization
decarburization depth

distance between the surface of a workpiece and a limit characterizing the thickness of the layer

depleted in carbon

Note 1 to entry: This limit varies according to the type of decarburization (3.54) and can be defined by reference

to a structural state, a level of hardness or the carbon content of the unaltered base metal (see ISO 3887), or any

other specified carbon content.
3.60
depth of hardening

distance between the surface of a workpiece and a limit characterizing the penetration of quench

hardening (3.167)

Note 1 to entry: This limit can be defined starting from a structural state or a level of hardness.

3.61
depth of nitriding
nitriding depth

distance between the surface of a workpiece and a specified limit characterizing the thickness of the

layer enriched in nitrogen
© ISO 2018 – All rights reserved 9
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SIST EN ISO 4885:2018
ISO 4885:2018(E)
3.62
destabilization of retained austenite

phenomenon occurring during tempering which allows the retained austenite (3.175) to undergo

martensitic transformation within a temperature range where it would not previously have been

transformed spontaneously
3.63
diffusion
movement of atoms to new places in ferrous materials
3.64
diffusion annealing

heat treatment (3.108)/annealing (3.8) of ferrous products or workpieces to reduce segregation (3.179)

and promote homogeneity by diffusion (3.63)

Note 1 to entry: To reduce segregation of metallic elements in steel making and in bar rolling a process with

temperatures between 1 000 °C and 1 300 °C is required.

Note 2 to entry: Reducing segregations of non-metallic alloying elements (such as carbon or sulfur) in workpieces

usually would be done at a temperature below 1 000 °C.
3.65
diffusion treatment

heat treatment (3.108) to reduce a very high concentration of elements in the surface layer such as

carbon or nitrogen after carburizing (3.36) or nitriding (3.143)

Note 1 to entry: See also malleablizing (3.133), which is also a diffusion treatment.

3.66
diffusion zone

surface layer formed by a thermochemical treatment (3.207) characterized by enrichment of elements

such as carbon or nitrogen

Note 1 to entry: The enriched elements such as carbon or nitrogen are in solid solution and/or precipitates such

as carbides or nitrides.

Note 2 to entry: The concentration of the enriched elements decreases from surface to the core of a workpiece.

3.67
direct-quench hardening

quench hardening (3.167) of carburized workpieces immediately after carburizing (3.36) or

carbonitriding (3.35)

Note 1 to entry: The direct-quench hardening should be started directly after carburizing or at a lower

temperature, adjusted to the surface carbon content.

Note 2 to entry: Direct hardening from hot forging or hot rolling replaces separate austenitizing (3.14) and

quenching (3.168).
Note 3 to entry: See Figure 1 a).
3.68
direct quenching

quenching (3.168) carried out immediately following hot rolling, hot forging or after a thermochemical

treatment (3.207) or solution annealing (3.188) of stainless
...