FprEN ISO 643

SLOVENSKI STANDARD
oSIST prEN ISO 643:2023
01-september-2023
Nadomešča:
SIST EN ISO 643:2020
Jekla - Mikrografsko določevanje navidezne velikosti kristalnih zrn (ISO/DIS
643:2023)
Steels - Micrographic determination of the apparent grain size (ISO/DIS 643:2023)
Stahl - Mikrophotographische Bestimmung der erkennbaren Korngröße (ISO/DIS
643:2023)
Aciers - Détermination micrographique de la grosseur de grain apparente (ISO/DIS
643:2023)
Ta slovenski standard je istoveten z: prEN ISO 643
ICS:
77.040.99 Druge metode za Other methods of testing of
preskušanje kovin metals
77.080.20 Jekla Steels
oSIST prEN ISO 643:2023 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

oSIST prEN ISO 643:2023
oSIST prEN ISO 643:2023
DRAFT INTERNATIONAL STANDARD
ISO/DIS 643
ISO/TC 17/SC 7 Secretariat: AFNOR
Voting begins on: Voting terminates on:
2023-07-17 2023-10-09
Steels — Micrographic determination of the apparent grain
size
Aciers — Détermination micrographique de la grosseur de grain apparente
ICS: 77.040.99
This document is circulated as received from the committee secretariat.
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NATIONAL REGULATIONS.
ISO/DIS 643:2023(E)
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oSIST prEN ISO 643:2023
ISO/DIS 643:2023(E)
DRAFT INTERNATIONAL STANDARD
ISO/DIS 643
ISO/TC 17/SC 7 Secretariat: AFNOR
Voting begins on: Voting terminates on:

Steels — Micrographic determination of the apparent grain
size
Aciers — Détermination micrographique de la grosseur de grain apparente
ICS: 77.040.99
This document is circulated as received from the committee secretariat.
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
© ISO 2023
ISO/CEN PARALLEL PROCESSING
THEREFORE SUBJECT TO CHANGE AND MAY
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NOT BE REFERRED TO AS AN INTERNATIONAL
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NATIONAL REGULATIONS.
Website: www.iso.org ISO/DIS 643:2023(E)
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ii
PROVIDE SUPPORTING DOCUMENTATION. © ISO 2023

oSIST prEN ISO 643:2023
ISO/DIS 643:2023(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 Grains . 1
3.2 General . 2
4 Symbols . 2
5 Principle . 3
6 Selection and preparation of the specimen. 5
6.1 Test location . 5
6.2 Revealing ferritic grain boundaries . 5
6.3 Revealing austenitic and prior-austenitic grain boundaries . 5
6.3.1 General . 5
7 Characterization of grain size .6
7.1 General . 6
7.1.1 Characterization methods . 6
7.1.2 Formulae . 6
7.1.3 Measurement uncertainty . 6
7.2 Comparison method . 6
7.3 Planimetric method . 9
7.4 Intercept method . 13
7.4.1 General .13
7.4.2 Linear intercept method . 14
7.4.3 Circular intercept method . 15
7.4.4 Assessment of results .15
7.5 Other methods . 16
8 Test report .17
Annex A (informative) Methods for revealing austenitic or prior-austenitic grain
boundaries in steels .18
Annex B (normative) Determination of grain size with standard comparison charts .23
Annex C (normative) Evaluation method .45
Annex D (informative) Calculation of grain size and confidence interval .47
Annex E (informative) Grains of different size indices .50
Bibliography .56
iii
oSIST prEN ISO 643:2023
ISO/DIS 643:2023(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
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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
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www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 17, Steel, Subcommittee SC 7, Methods of
testing (other than mechanical tests and chemical analysis).
This fifth edition cancels and replaces the fourth edition (ISO 643:2019), which has been technically
revised.
The main changes are as follows:
— the test temperature of McQuaid-Ehn method has been increased to 950 °C (see 6.3.4);
— subclause 7.1.2 has been modified with reference to new Annex B and amended Table 2;
— Annex B from the third edition (ISO 643:2012) has been reinstated, now with new ISO grain size
charts instead of ASTM charts;
— the old Annex B (evaluation method) has been renumbered as Annex C. New Formulas (C.8) and
(C.9) and amended Table C.1 have been introduced.
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
oSIST prEN ISO 643:2023
DRAFT INTERNATIONAL STANDARD ISO/DIS 643:2023(E)
Steels — Micrographic determination of the apparent grain
size
WARNING — This document calls for the use of substances and/or procedures that may
be injurious to health if adequate safety measures are not taken. This document does not
address any health hazards, safety or environmental matters associated with its use. It is
the responsibility of the user of this document to establish appropriate health, safety and
environmentally acceptable practices.
1 Scope
This document specifies a micrographic method of determining apparent ferritic or austenitic grain
size in steels. It describes the methods of revealing grain boundaries and of estimating the mean grain
size of specimens with unimodal size distribution. Although grains are three-dimensional in shape,
the metallographic sectioning plane can cut through a grain at any point from a grain corner, to the
maximum diameter of the grain, thus producing a range of apparent grain sizes on the two-dimensional
plane, even in a sample with a perfectly consistent grain size.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
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