prEN ISO 4491-3

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

FINAL DRAFT
International
Standard
ISO/FDIS 4491-3
ISO/TC 119/SC 2
Metallic powders — Determination
Secretariat: SIS
of oxygen content by reduction
Voting begins on:
methods —
Part 3:
Voting terminates on:
Hydrogen-reducible oxygen
Poudres métalliques — Dosage de l'oxygène par les méthodes de
réduction —
Partie 3: Oxygène réductible par l'hydrogène
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/CEN PARALLEL PROCESSING LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
ISO/FDIS 4491-3:2025(en) © ISO 2025

FINAL DRAFT
ISO/FDIS 4491-3:2025(en)
International
Standard
ISO/FDIS 4491-3
ISO/TC 119/SC 2
Metallic powders — Determination
Secretariat: SIS
of oxygen content by reduction
Voting begins on:
methods —
Part 3:
Voting terminates on:
Hydrogen-reducible oxygen
Poudres métalliques — Dosage de l'oxygène par les méthodes de
réduction —
Partie 3: Oxygène réductible par l'hydrogène
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-
ISO/CEN PARALLEL PROCESSING
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland Reference number
ISO/FDIS 4491-3:2025(en) © ISO 2025

ii
ISO/FDIS 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 . 7
8 Procedure . 7
9 Calculation and expression of test results . 9
10 Test report . 10

iii
ISO/FDIS 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 ISO 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/FDIS 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
FINAL DRAFT International Standard ISO/FDIS 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 — Part 1: General
guidelines
3 Terms and definitions
No terms and definitions are listed in this document.
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/
4 Principle
Pre-treatment of a test portion by drying at low temperature (170 °C) in dry nitrogen or argon.
Reduction in a stream of pure dry hydrogen at a given temperature. Absorption in methanol of the water
formed by reaction of oxides with hydrogen. Titration with Karl Fischer reagent, the end-point being
determined either visually by the colour change or electrometrically with two electrodes (deadstop end-
point). ISO 760 and ISO 4491-1 shall be used in conjunction with this document.
For powders containing carbon, conversion of the carbon monoxide and carbon dioxide formed to methane
and water at 380 °C a nickel catalyst.

ISO/FDIS 4491-3:2025(en)
5 Reagents
During the analysis, use only reagents of recognized analytical grade and only distilled water or water of
equivalent purity.
WARNING — Karl Fischer reagent contains four toxic compounds: iodine, sulfur dioxide, pyridine
and methanol. It is important to avoid direct contact and especially inhalation. Following accidental
spillage, rinse with plenty of water.
5.1 Methanol, anhydrous.
5.2 Karl Fischer reagent, equivalent to 1 mg of oxygen per millilitre. Determine the titre of the Karl
Fischer reagent by one of the following methods:
a) Add to the titration flask 20 mg to 30 mg of water, weighed to the nearest 0,1 mg
b) Add 100 mg to 200 mg, weighed to the nearest 0,1 mg of sodium tartrate dihydrate (certified material
containing theoretically a mass percentage of 15,66 % of water, corresponding to a mass percentage of
13,92 % of oxygen), previously ground to fine powder and dried at 105 °C ± 5 °C to constant mass
c) Use the method described in Clause 8, taking 100 mg to 200 mg of pure sodium tartrate dihydrate,
weighed to the nearest 0,1 mg, as the test portion, but limiting the procedure to the drying step at 170 °C
and the subsequent titration.
See ISO 760 for detailed procedures of standardization.
5.3 Hydrogen, having a maximum oxygen content mass percentage of 0,005 % and a dew point not
exceeding -45 °C.
5.4 Nitrogen or argon, having a maximum oxygen content mass p
...