ISO 24251-1
(Main)Prevention of hydrogen assisted brittle fracture of high-strength steel components — Part 1: Fundamentals and measures
Prevention of hydrogen assisted brittle fracture of high-strength steel components — Part 1: Fundamentals and measures
This document gives guidelines for prevention of hydrogen assisted brittle fracture resulting from the manufacturing process (internal hydrogen embrittlement (IHE)). This document is applicable for parts or components made of high strength steels. It also advises on the relationship between material selection, manufacture including heat treatment, and coating.
Prévention de la fragilisation par l'hydrogène des pièces en acier à haute résistance — Partie 1: Principes fondamentaux et mesures
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FINAL DRAFT
International
Standard
ISO/FDIS 24251-1
ISO/TC 107/SC 3
Prevention of hydrogen assisted
Secretariat: KATS
brittle fracture of high-strength
Voting begins on:
steel components —
2025-04-25
Part 1:
Voting terminates on:
2025-06-20
Fundamentals and measures
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MADE IN NATIONAL REGULATIONS.
Reference number
ISO/FDIS 24251-1:2025(en) © ISO 2025
FINAL DRAFT
ISO/FDIS 24251-1:2025(en)
International
Standard
ISO/FDIS 24251-1
ISO/TC 107/SC 3
Prevention of hydrogen assisted
Secretariat: KATS
brittle fracture of high-strength
Voting begins on:
steel components —
Part 1:
Voting terminates on:
Fundamentals and measures
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 2025
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-
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: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland Reference number
ISO/FDIS 24251-1:2025(en) © ISO 2025
ii
ISO/FDIS 24251-1:2025(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 4
5 Fundamentals . 5
5.1 General description of hydrogen embrittlement .5
5.2 Conditions for hydrogen embrittlement failure .5
5.2.1 General .5
5.2.2 Material susceptibility .6
5.2.3 Tensile stress .7
5.2.4 Sources of atomic hydrogen .7
5.3 Mechanism of hydrogen embrittlement of high strength steel .8
5.4 Fundamentals of metallic coatings regarding hydrogen uptake and diffusion .9
5.4.1 General aspects of metallic electroplated protection layers .9
5.4.2 Hydrogen generation during coating process .9
5.4.3 Corrosion protection mechanisms by metallic layers .9
6 Preventive measures with regard to hydrogen embrittlement .12
6.1 General . 12
6.2 Part design and manufacturing. 13
6.3 Material related measures and heat treatment . 13
6.4 Reduction of residual tensile stress (stress relief) .14
6.5 Measures related to coating processes .14
6.5.1 General .14
6.5.2 Pre-treatment — Cleaning processes . 15
6.5.3 Electroplating coating processes. 15
6.5.4 Stripping of coatings . 15
6.5.5 Corrective actions – Baking .16
6.6 Prevention of environmental hydrogen uptake .17
6.6.1 General .17
6.6.2 Environmentally appropriate design .17
Annex A (informative) Electroplating processes .18
Annex B (informative) Principles of electrochemical corrosion.20
Bibliography .23
iii
ISO/FDIS 24251-1:2025(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 107, Metallic and other inorganic coatings,
Subcommittee SC 3, Electrodeposited coatings and related finishes.
A list of all parts in the ISO 24251 series can be found on the ISO website.
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
ISO/FDIS 24251-1:2025(en)
Introduction
High strength steel parts or components are broadly characterized by tensile strengths (Rm) above
1 000 MPa. They are often used in critical applications, such as in bridges, engines and aircraft, where a
failure can have catastrophic consequences. Preventing failures and managing the risk of hydrogen
embrittlement (HE) is a fundamental consideration that implicates the entire supply chain, including steel
mills, part manufacturers, coaters, application engineers, designers and end users.
HE has been studied for decades, yet the complex nature of HE phenomena and the many variables make it
hard to predict HE failures. Research is typically conducted under conditions that are either simplified or
idealized or both, and the findings cannot be effectively prescribed in industry standards and practices.
Circumstances are further complicated by specifications or standards that are sometimes either inadequate
or unnecessarily alarmist or both. Inconsistencies and even contradictions in industry standards have led to
much confusion and many preventable HE failures. The fact that HE is very often mistakenly determined to
be the root cause of failure as opposed to a mechanism of failure reflects the confusion.
v
FINAL DRAFT International Standard ISO/FDIS 24251-1:2025(en)
Prevention of hydrogen assisted brittle fracture of high-
strength steel components —
Part 1:
Fundamentals and measures
1 Scope
This document provides guidance on the prevention of hydrogen assisted brittle fracture, known as
hydrogen embrittlement (HE), that results from the manufacturing process or operating conditions.
This document is applicable to components or parts made of high strength steels.
This document provides guidance on the relationship between material selection, manufacturing (including
heat treatment) and coating.
NOTE 1 For hot-dip galvanizing components, see ISO 14713-2.
NOTE 2 This document does not consider applications under pressurised hydrogen.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 2080, Metallic and other inorganic coatings — Surface treatment, metallic and other inorganic coatings —
Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 2080 and the following apply.
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
hardness
resistance of a metal to plastic deformation, usually by indentation or penetration by a solid object (at the
surface or in the core)
3.2
work hardening
increase of mechanical strength and hardness (3.1) when a metal is plastically d
...
ISO/FDIS 24251-1:2024(en)
ISO /TC 107/SC 3/WG 3
Secretariat: KATS
Date: 2024-03-192025-04-11
2024-07-30
Prevention of hydrogen assisted brittle fracture of high-strength
steel components —
Part 1:
Fundamentals and measures
FDIS stage
ISO/FDIS 24251-1:2025(en)
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
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
Fax: +41 22 749 09 47
EmailE-mail: copyright@iso.org
Website: www.iso.orgwww.iso.org
Published in Switzerland
ii © ISO 2024 2025 – All rights reserved
ii
ISO/DIS FDIS 24251-1:20242025(en)
Contents
Foreword . v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 5
5 Fundamentals . 5
5.1 General description of hydrogen embrittlement . 5
5.2 Conditions for hydrogen embrittlement failure . 6
5.3 Mechanism of hydrogen embrittlement of high strength steel . 10
5.4 Fundamentals of metallic coatings regarding hydrogen uptake and diffusion . 11
6 Preventive measures with regard to hydrogen embrittlement . 16
6.1 General . 16
6.2 Part design and manufacturing . 17
6.3 Material related measures and heat treatment . 17
6.4 Reduction of residual tensile stress (stress relief) . 18
6.5 Measures related to coating processes . 18
6.6 Prevention of environmental hydrogen uptake . 21
Annex A (informative) Electroplating processes . 23
Annex B (informative) Principles of electrochemical corrosion . 25
Bibliography . 29
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 5
5 Fundamentals . 6
5.1 General description of hydrogen embrittlement . 6
5.2 Conditions for hydrogen embrittlement failure . 6
5.2.1 General . 6
5.2.2 Material susceptibility . 7
5.2.3 Tensile stress . 7
5.2.4 Sources of atomic hydrogen . 8
5.3 Mechanism of hydrogen embrittlement of high strength steel . 9
5.4 Fundamentals of metallic coatings with regard to hydrogen uptake and diffusion . 10
5.4.1 General aspects of metallic electroplated protection layers . 10
5.4.2 Hydrogen generation during coating process . 10
5.4.3 Corrosion protection mechanisms by metallic layers . 10
5.4.4 Hydrogen formation by corrosion . 12
6 Preventive measures with regard to hydrogen embrittlement . 13
6.1 General . 13
iii
ISO/FDIS 24251-1:2025(en)
6.2 Part Design and Manufacturing . 13
6.3 Material related measures and heat treatment . 14
6.4 Reduction of residual tensile stress (stress relief) . 14
6.5 Measures related to coating processes . 15
6.5.1 General . 15
6.5.2 Pre-treatment – Cleaning processes . 15
6.5.3 Electroplating coating processes . 16
6.5.4 Stripping of coatings . 16
6.5.5 Corrective actions – Baking . 17
6.6 Prevention of environmental hydrogen uptake . 18
6.6.1 General . 18
6.6.2 Environmentally appropriate design . 18
7 Test categories . 18
Annex A (informativ) Electroplating processes . 19
A.1 General . 19
A.2 Exemplary characteristics of electroplating processes . 19
A.2.1 Example 1 - Mild acid zinc . 19
A.2.2 Example 2 - Alkaline zinc (cyanide free) . 19
Annex B (informativ) Principles of electrochemical corrosion . 21
Bibliography . 24
iv © ISO 2024 2025 – All rights reserved
iv
ISO/DIS FDIS 24251-1:20242025(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.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.htmlwww.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 107, Metallic and other inorganic coatings,
Subcommittee SC 3, Electrodeposited coatings and related finishes.
A list of all parts in the ISO 24251 series can be found on the ISO website.
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.htmlwww.iso.org/members.html.
v
ISO/FDIS 24251-1:2025(en)
Introduction
High strength steel parts or components are broadly characterized by tensile strengths (Rm) above 1 000 MPa
and. They are often used in critical applications, such as in bridges, engines, and aircraft, where a failure can
have catastrophic consequences. Preventing failures and managing the risk of hydrogen embrittlement (HE)
is a fundamental consideration implicatingthat implicates the entire supply chain, including: the steel mill,
themills, part manufacturer, the coater, themanufacturers, coaters, application engineer, the designer, all the
way to the engineers, designers and end user. Hydrogen embrittlementusers.
HE has been studied for decades, yet the complex nature of HE phenomena and the many variables make the
occurrence ofit hard to predict HE failures unpredictable. Research is typically conducted under conditions
that are either under simplified or idealized conditions, or both that , and the findings cannot be effectively
translated into know-how prescribed in industry standards and practices. Circumstances are further
complicated by specifications or standards that are sometimes either inadequate or unnecessarily alarmist,
or both. Inconsistencies and even contradictions in industry standards have led to much confusion and many
preventable HE failures. The fact that HE is very often mistakenly determined to be the root cause of failure
as opposed to a mechanism of failure reflects the
...
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