SIST EN ISO 4491-3:2025

SLOVENSKI STANDARD
01-december-2025
Kovinski praški - Določanje kisika z redukcijskimi metodami - 3. del: Kisik,
reduciran z vodikom (ISO 4491-3:2025)
Metallic powders - Determination of oxygen content by reduction methods - Part 3:
Hydrogen-reducible oxygen (ISO 4491-3:2025)
Metallpulver - Bestimmung des Sauerstoffgehaltes durch Reduktionsverfahren - Teil 3:
Wasserstoffreduzierbarer Sauerstoff (ISO 4491-3:2025)
Poudres métalliques - Dosage de l'oxygène par les méthodes de réduction - Partie 3:
Oxygène réductible par l'hydrogène (ISO 4491-3:2025)
Ta slovenski standard je istoveten z: EN ISO 4491-3:2025
ICS:
77.160 Metalurgija prahov Powder metallurgy
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 4491-3
EUROPEAN STANDARD
NORME EUROPÉENNE
September 2025
EUROPÄISCHE NORM
ICS 77.160 Supersedes EN ISO 4491-3:2006
English Version
Metallic powders - Determination of oxygen content by
reduction methods - Part 3: Hydrogen-reducible oxygen
(ISO 4491-3:2025)
Poudres métalliques - Dosage de l'oxygène par les Metallpulver - Bestimmung des Sauerstoffgehaltes
méthodes de réduction - Partie 3: Oxygène réductible durch Reduktionsverfahren - Teil 3:
par l'hydrogène (ISO 4491-3:2025) Wasserstoffreduzierbarer Sauerstoff (ISO 4491-
3:2025)
This European Standard was approved by CEN on 19 September 2025.

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
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 4491-3:2025 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 4491-3:2025) has been prepared by Technical Committee ISO/TC 119 "Powder
metallurgy" in collaboration with CCMC.
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 March 2026, and conflicting national standards shall
be withdrawn at the latest by March 2026.
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 4491-3:2006.
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 4491-3:2025 has been approved by CEN as EN ISO 4491-3:2025 without any
modification.
International
Standard
ISO 4491-3
Third edition
Metallic powders — Determination
2025-09
of oxygen content by reduction
methods —
Part 3:
Hydrogen-reducible oxygen
Poudres métalliques — Dosage de l'oxygène par les méthodes de
réduction —
Partie 3: Oxygène réductible par l'hydrogène
Reference number
ISO 4491-3:2025(en) © ISO 2025

ISO 4491-3:2025(en)
© ISO 2025
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
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 4491-3:2025(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents . 2
6 Apparatus . 2
7 Sampling . 6
8 Procedure . 6
9 Calculation and expression of test results . 9
10 Test report . 9

iii
ISO 4491-3:2025(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 119, Powder metallurgy, Subcommittee SC
2, Sampling and testing methods for powders (including powders for hardmetals), in collaboration with the
European Committee for Standardization (CEN), in accordance with the Agreement on technical cooperation
between ISO and CEN (Vienna Agreement).
This third edition cancels and replaces the second edition (ISO 4491-3:1997), of which it constitutes a minor
revision.
The main changes are as follows:
— normative references in Clause 2 have been updated;
— editorial revisions and alignment with current ISO drafting directives.
A list of all parts in the ISO 4491 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 4491-3:2025(en)
Introduction
This document is intended to be used for the determination of hydrogen reducible oxygen content of metallic
powders, including powders containing carbon.
If carbon is present in the powder, some metal oxides which can otherwise have been reduced by hydrogen
are instead reduced by carbon, producing carbon monoxide or carbon dioxide. These products are not
measured by the titration with Karl Fischer reagent which is used to determine the amount of water
produced. Consequently, a lower result will be obtained for the hydrogen-reducible oxygen content.
This interference is eliminated by passing the gases emerging from the reduction furnace over a catalyst
which converts the CO and C0 formed into methane and water, in accordance with the following equations:
CO+→3HCHH+ O
24 2
CO +→42HCHH+ O
22 42
The conversion reaction is carried out at 380 °C, over a nickel catalyst.
Certain oxides can be partially reduced by carbon which otherwise would not be reduced by hydrogen. In
such cases the interpretation of results should be made with great care (see ISO 4491-1:2023, 5.1.2 d).

v
International Standard ISO 4491-3:2025(en)
Metallic powders — Determination of oxygen content by
reduction methods —
Part 3:
Hydrogen-reducible oxygen
1 Scope
This document specifies a method for the determination of the hydrogen-reducible oxygen content of
metallic powders containing mass percentage of 0,05 % to 3 % oxygen.
This document is applicable to unalloyed, partially alloyed or completely alloyed metal powders and also to
mixtures of carbides and binder metal. This document is not applicable to powders containing lubricants or
organic binders.
This document can be extended to powders containing carbon by the use of a special catalytic device. This
document is intended to be used in conjunction with ISO 760 and ISO 4491-1.
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 760, Determination of water — Karl Fischer method (General method)
ISO 4491-1, Metallic powders — Determination of oxygen content by reduction methods —
...