ISO/FDIS 14250
(Main)Steel — Metallographic characterization of duplex grain size and distributions
- Abstract
This International Standard specifies a micrographic method of determining the duplex grain size of rolled or forged steel products using standard diagrams or by the point count procedure.
- Status
- Not Published
- Current Stage
- 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
- Start Date
- 24-Aug-2026
- Completion Date
- 24-Aug-2026
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ISO/FDIS 14250 - Steel — Metallographic characterization of duplex grain size and distributions
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ISO/FDIS 14250 is an ISO standard for metallographic characterization of duplex grain size in rolled or forged steel products. It specifies a micrographic method for determining duplex grain size and the area fraction of the different grain-size regions, using standard diagrams or the point count procedure. It is intended for people who need to identify, measure, and report non-uniform grain-size distributions in steel.
What does ISO/FDIS 14250 specify?
ISO/FDIS 14250 specifies a micrographic method for determining duplex grain size, including area fraction, in rolled or forged steel products. It also gives detailed methods for the different kinds of duplex grain size so that the result can be described in a consistent way.
The document is organized into clauses for scope, normative references, terms and abbreviations, principle, apparatus, sampling and preparation, procedure, and test report. It has two annexes: one normative annex for area-fraction charts and one informative annex for a grain-size-distribution classification procedure.
| Annex | What it covers |
|---|---|
| Annex A | Chart for estimation of area fractions |
| Annex B | Classification procedure for grain size distributions |
What are the key requirements of ISO/FDIS 14250?
ISO/FDIS 14250 sets out how to recognize duplex grain size, how to measure the size of the different grain populations, and how to report the result. In practice, that means the operator must decide whether the structure is random or topological, measure the relevant grain-size regions with the appropriate method, and record the area fractions and grain-size indices in a fixed format.
Sampling and specimen preparation
ISO/FDIS 14250 requires evaluation of the entire specimen surface when the goal is to characterize deviations from a single log-normal grain-size distribution or patterns of variation. The examined surface is taken along the longitudinal direction in a plane parallel to the direction of maximum deformation, except for bars and tubes, where the surface is perpendicular to that direction.
The specimen must be polished and etched long enough to make all, or nearly all, grain boundaries visible. For the user, this matters because poor preparation or the wrong section plane can hide duplex features or distort the measured distribution.
Recognizing duplex grain size
ISO/FDIS 14250 divides duplex grain size into two main classes: random duplex grain size and topological duplex grain size. Random duplex grain size includes ALA, WR, and BM conditions; topological duplex grain size includes CS, NL, and BD conditions.
That classification is practical because each type is measured and reported differently. For example, ALA focuses on isolated coarse grains, while BD and CS describe grain-size changes linked to position in the product cross-section.
Estimating area fractions
ISO/FDIS 14250 gives several ways to estimate the area fraction occupied by a distinct grain-size region. The comparison procedure uses the charts in Annex A, the point count procedure follows ISO 9042, the planimetric procedure uses outlined areas on images, and a direct measurement procedure applies only to topological duplex specimens with surface layers of differing grain size.
For random duplex grain size, the comparison procedure uses at least five randomly selected areas; for topological duplex grain size, it is applied to the entire specimen area. This matters in practice because the sampling pattern affects how well the measured area fraction represents the full product.
Determining grain size
ISO/FDIS 14250 uses the methods of ISO 643 to determine apparent grain size (AGS) for the relevant grain populations. For ALA grains, the standard links the ALA grain size index to the largest grain on the inspection surface and allows diameter, planimetric, image analysis, and test grid methods, with the test grid method as the referee procedure in a dispute.
For other duplex cases, the standard directs the user to rate the grain sizes in representative fields and, where needed, to distinguish the grain populations separately. In practice, this gives a consistent way to compare the matrix grains with the abnormal or distinct grain-size regions.
Reporting the result
ISO/FDIS 14250 requires the report to identify the steel grade, specimen orientation, duplex type, method used, percentage in surface, and grain size. It also gives standard report formats for ALA, WR, BM, CS, NL, and BD conditions.
This is important because the report is not just a micrograph interpretation - it is a structured result that can be compared between laboratories, product batches, and suppliers.
What terms does ISO/FDIS 14250 define?
ISO/FDIS 14250 defines duplex grain size as a grain-size condition where the distribution of intercept lengths, diameters, or areas departs from a single lognormal distribution. That definition is the basis for deciding whether a steel product falls into the document’s scope.
Equivalent diameter is the diameter of a circle with the same area as the grain. The standard uses this idea when rating grain size from grain shape measurements.
Random duplex grain size means two or more significantly different grain sizes that are distributed randomly. This is the category used when the coarse and fine grains are mixed without a fixed pattern.
Topological duplex grain size means two or more significantly different grain sizes that follow a non-random, definable pattern. This covers cases such as surface-to-core variation, necklaces, and banding.
ALA means as large as and is used for isolated coarse grains. AGS means apparent grain size, the grain-size rating taken from ISO 643 for the relevant region.
BM means bimodal, CS means cross-section, NL means necklace, and BD means banding. These symbols are used in the report format so the duplex type can be identified quickly and unambiguously.
Who uses ISO/FDIS 14250?
ISO/FDIS 14250 is used by metallography and materials-testing laboratories, steel producers, and quality teams that need to describe non-uniform grain structures in rolled or forged steel. It is also relevant to inspectors and technical buyers who review test reports and need a common vocabulary for duplex grain-size conditions.
The standard is useful when a product specification, internal control plan, or investigation needs a repeatable way to document grain-size variation across a specimen. In practice, it supports comparison between samples, suppliers, and heat-treatment or forming conditions.
What changed in ISO/FDIS 14250 from the previous edition?
ISO/FDIS 14250 is the second edition and cancels and replaces ISO 14250:2000. The foreword states that it has been technically revised.
The main changes listed are:
- added terms and definitions, the principle, and the procedure clauses, with subsequent clauses renumbered
- clarified the method for determining grain size using ISO 643
- modified all figures
- clarified the planimetric procedure for estimating area fraction
- clarified the determination of isolated coarse grain size
- clarified the determination of apparent grain size other than ALA grains
- clarified the characterization of duplex grain size and distributions
- modified the area-fraction charts in Annex A
- added the grain-size-distribution classification procedure in Annex B
Which standards are used with ISO/FDIS 14250?
ISO/FDIS 14250 cites ISO 643 and ISO 9042 as normative references.
ISO 643, Steels - Micrographic determination of the apparent grain size, provides the grain-size rating methods used for the matrix grains and for other distinct grain populations. ISO/FDIS 14250 relies on it for rating chart, planimetric, intercept, and related approaches.
ISO 9042, Steels - Point counting method for statistically estimating the volume fraction of a constituent with a point grid, provides the point-count framework used to estimate area fraction in duplex grain-size evaluation. In practice, it supports the grid-based counting method and the way the result is recorded.
What does the ISO/FDIS 14250 document contain?
ISO/FDIS 14250 contains the procedure for identifying duplex grain size, the apparatus needed for comparison charts and point counting, and the sampling and preparation rules for micrographic examination. It also includes procedures for recognizing the main duplex classes, estimating area fractions, determining ALA grain size, and rating apparent grain size for the different grain-size populations.
The document includes a table of abbreviated terms, a table linking ALA grain size to equivalent diameter and area, and a set of figures showing the main duplex conditions and the grid-based ALA procedure. Annex A provides the comparison chart for area-fraction estimation, and Annex B gives the classification procedure for grain-size distributions.
Clause 9 gives the report content and standard report formats, so users can document results in a consistent way. That makes the standard useful both for lab work and for formal test reporting across the steel supply chain.
Relations
- Revises
ISO 14250:2000 - Steel — Metallographic characterization of duplex grain size and distributions - Effective Date
- 23-Dec-2023
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ISO/FDIS 14250 - Steel — Metallographic characterization of duplex grain size and distributions
REDLINE ISO/FDIS 14250 - Steel — Metallographic characterization of duplex grain size and distributions
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Frequently Asked Questions
ISO/FDIS 14250 is a draft published by the International Organization for Standardization (ISO). Its full title is "Steel — Metallographic characterization of duplex grain size and distributions". This standard covers: This International Standard specifies a micrographic method of determining the duplex grain size of rolled or forged steel products using standard diagrams or by the point count procedure.
This International Standard specifies a micrographic method of determining the duplex grain size of rolled or forged steel products using standard diagrams or by the point count procedure.
ISO/FDIS 14250 is classified under the following ICS (International Classification for Standards) categories: 77.080.20 - Steels. The ICS classification helps identify the subject area and facilitates finding related standards.
ISO/FDIS 14250 has the following relationships with other standards: It is inter standard links to ISO 14250:2000. Understanding these relationships helps ensure you are using the most current and applicable version of the standard.
ISO/FDIS 14250 is available in PDF format for immediate download after purchase. The document can be added to your cart and obtained through the secure checkout process. Digital delivery ensures instant access to the complete standard document.
Standards Content (Sample)
FINAL DRAFT
International
Standard
ISO/TC 17/SC 7
Steel — Metallographic
Secretariat: AFNOR
characterization of duplex grain
Voting begins on:
size and distributions
2026-08-24
Aciers — Caractérisation métallographique de la grosseur et de
Voting terminates on:
la distribution de grain duplex
2026-10-19
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
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
FINAL DRAFT
International
Standard
ISO/TC 17/SC 7
Steel — Metallographic
Secretariat: AFNOR
characterization of duplex grain
Voting begins on:
size and distributions
Aciers — Caractérisation métallographique de la grosseur et de
Voting terminates on:
la distribution de grain duplex
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 2026
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
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 2
5 Principle . 2
6 Apparatus . 3
6.1 General .3
6.2 Comparison procedure for estimation of area fractions .3
6.3 Point count procedure for estimation of area fractions .3
6.4 Determination of grain size .3
7 Sampling and preparation of test specimens . 3
8 Procedure . 3
8.1 Recognizing and classifying duplex grain size .3
8.1.1 Random duplex grain size .3
8.1.2 Topological duplex grain size .4
8.2 Estimation of area fractions .7
8.2.1 Comparison procedure .7
8.2.2 Point count procedure .7
8.2.3 Planimetric procedure .8
8.2.4 Direct measurement procedure .8
8.3 Determination of grain size .8
8.3.1 Determination of isolated coarse grain size .8
8.3.2 Apparent grain size other than ALA grains .10
8.4 Characterization of duplex grain size and distributions .11
8.4.1 Random duplex grain size .11
8.4.2 Topological duplex grain size . 12
9 Test report .12
Annex A (normative) Chart for estimation of area fractions .13
Annex B (informative) Classification procedure for grain size distributions .15
iii
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).
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 17, Steel, Subcommittee SC 7, Methods of testing
(other than mechanical tests and chemical analysis).
This second edition cancels and replaces the first edition (ISO 14250:2000), which has been technically
revised.
The main changes are as follows:
— adding terms and definitions (Clause 3), principles (Clause 5) and procedure (Clause 8), and renumbering
the subsequent clauses;
— clarifying the specific method for determining grain size using ISO 643;
— modifying all of the figures;
— clarifying the planimetric procedure of estimation of area fraction;
— clarifying the determination of isolated coarse grain size;
— clarifying the determination of apparent grain size other than ALA grains;
— clarifying the characterization of duplex grain size and distributions;
— modifying the charts for estimation of area fractions in Annex A;
— adding the classification procedure for grain size distributions in Annex B.
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
FINAL DRAFT International Standard ISO/FDIS 14250:2026(en)
Steel — Metallographic characterization of duplex grain size
and distributions
1 Scope
This document specifies a micrographic method of determining the duplex grain size including the area
fraction, of rolled or forged steel products.
Additionally, this document provides detailed description methods for each specific type of duplex grain
size.
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 643, Steels — Micrographic determination of the apparent grain size
ISO 9042, Steels — Point counting method for statistically estimating the volume fraction of a constituent with
a point grid
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:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
duplex grain size
condition existent when the distribution of grain intercept lengths, diameters or areas deviates from a single
lognormal distribution
Note 1 to entry: Various types of duplex grain sizes are described in 8.1.
3.2
equivalent diameter
diameter of a circle with an area equivalent to that of the grain
Note 1 to entry: The area is calculated as the geometric mean of the long axis (the maximum chord length) and the
short axis (the maximum chord length perpendicular to the long axis), obtained by multiplying the two axes and
taking the square root of the product.
3.3
random duplex grain size
grains of two or more significantly different sizes that are randomly distributed
Note 1 to entry: See 5.1 for further explanations.
3.4
topological duplex grain size
grains of two or more significantly different sizes that vary in a non-random, definable pattern
Note 1 to entry: See 5.1 for further explanations.
4 Abbreviated terms
The abbreviated terms used are given in Table 1
Table 1 — Abbreviated terms
Terms Definition
ALA As large as
AGS Apparent grain size
BD Banding
BM Bi Modal
CS Cross section
DG Duplex grain
L Longitudinal
NL Necklace
T Transverse
WR Wide range
G ALA grain size
ALA
G AGS grain size
5 Principle
5.1 Duplex grain size is classified into two main categories: random duplex grain size and topological
duplex grain size, each with specified subcategories. Random duplex grain size includes: Individual coarse
grains (ALA), Wide range grains (WR) and Bimodal grains (BM). Topological duplex grain size includes:
Cross-section variations of grains (CS), Necklace grains (NL) and Grains in bands (BD). This pattern may be
related to the shape of the product being examined or the factors influencing grain formation. The document
specifies methods for analysing the distribution type, rating the grain size, and estimating the area fractions
occupied by each distinct grain size type. See Figure B.1 in Annex B for the classification procedure for grain
size distribution.
5.2 This document outlines methods for identifying the presence of duplex grain size and characterizing
the features of specific types of duplex grain sizes. It includes procedures for estimating the area fractions
occupied by distinct grain sizes. The document establishes test methods for determining ALA grain size and
provides guidelines for applying ISO 643 to determine grain size in specific designated areas. Additionally,
it offers methods for reporting detailed and distinctive information for each type of duplex grain size.
Furthermore, the test methods provide a statistical procedure for determining the actual distribution of all
grain sizes present in a duplex grain size specimen.
5.3 The method may be applied to specimens or products containing grains of two or more significantly
different sizes, but distributes at random or in topologically varying patterns.
5.4 The total specimen surface shall be evaluated when the test method describes deviations from a
single, log-normal distribution of grain sizes and characterizes pattern of variations in grain size.
6 Apparatus
6.1 General
The apparatus used shall depend on the nature of the test method as described in 6.2 to 6.4.
6.2 Comparison procedure for estimation of area fractions
This procedure shall require the use of comparison charts presented in Annex A, Figure A.1 to improve the
accuracy of visual estimates of area fractions occupied by a distinct grain size. These comparison charts
show different area percentages of light grains among dark grains.
6.3 Point count procedure for estimation of area fractions
This procedure shall require the use of a test grid on a transparent overlay, or on a reticle, as specified in
ISO 9042.
6.4 Determination of grain size
The devices specified in ISO 643 shall be used. For specimens exhibiting different grain size distributions,
the test methods outlined in ISO 643 — such as the rating chart method, planimetric method, or intercept
method — shall be employed to rate the distinct grain sizes. Additionally, the intercept length method
described in ISO 643:2024, Annex E, may also be utilized for this purpose. When rating individual ALA
grains, the assessment shall be based on the equivalent diameter or the area of the maximum grain.
7 Sampling and preparation of test specimens
In order to characterize patterns of duplex grain size the entire cross section of the specimen from the
product shall be evaluated. The examined surface shall be along the longitudinal direction in a plane parallel
to the direction of maximum product deformation except in the case of bars and tubes where the examined
surface shall be perpendicular to the direction of the maximum deformation. The number of test specimens
and their location shall be specified in the relevant product standard. When it is not the case, they are left at
the producer's discretion.
A flat surface of the test specimen shall be polished for micrographic examination and shall be etched for an
adequate period of time by means of the appropriate etching. The etch shall be such that all, or nearly all, of
the grain boundaries are visible.
8 Procedure
8.1 Recognizing and classifying duplex grain size
8.1.1 Random duplex grain size
8.1.1.1 General
A random duplex grain sizes is defined as any of the following.
8.1.1.2 Random coarse grains(ALA)
This is the presence of randomly distributed individual coarse grains, differing in size by three or more ISO
grain size numbers from the average size of the bal
...
ISO/TC 17/SC 7/WG 7
Secretariat: AFNOR
Date: 2026-07-1608-10
Steel — Metallographic characterization of duplex grain size and
distributions
Aciers — Caractérisation métallographique de la grosseur et de la distribution de grain duplex
FDIS stage
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
EmailE-mail: copyright@iso.org
Website: www.iso.orgwww.iso.org
Published in Switzerland
ii
Contents
Foreword . iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 2
5 Principle . 2
6 Apparatus . 3
6.1 General. 3
6.2 Comparison procedure for estimation of area fractions . 3
6.3 Point count procedure for estimation of area fractions . 3
6.4 Determination of grain size. 3
7 Sampling and preparation of test specimens . 3
8 Procedure . 3
8.1 Recognizing and classifying duplex grain size . 3
8.2 Estimation of area fractions . 11
8.3 Determination of grain size. 12
8.4 Characterization of duplex grain size and distributions . 16
9 Test report . 17
Annex A (normative) Chart for estimation of area fractions . 19
Annex B (informative) Classification procedure for grain size distributions . 23
iii
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).
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 17, Steel, Subcommittee SC 7, Methods of testing
(other than mechanical tests and chemical analysis).
This second edition cancels and replaces the first edition (ISO 14250:2000), which has been technically
revised.
The main changes are as follows:
— — adding terms and definitions (Clause 3(Clause 3),), principles (Clause 5(Clause 5)) and procedure
(Clause 8(Clause 8),), and renumbering the subsequent clauses;
— — clarifying the specific method for determining grain size using ISO 643;
— — modifying all of the figures;
— — clarifying the planimetric procedure of estimation of area fraction;
— — clarifying the determination of isolated coarse grain size;
— — clarifying the determination of apparent grain size other than ALA grains;
— — clarifying the characterization of duplex grain size and distributions;
— — modifying the charts for estimation of area fractions in Annex AAnnex A;;
— — adding the classification procedure for grain size distributions in Annex BAnnex B.
iv
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.
v
Steel — Metallographic characterization of duplex grain size and
distributions
1 Scope
This document specifies a micrographic method of determining the duplex grain size including the area
fraction, of rolled or forged steel products.
Additionally, this document provides detailed description methods for each specific type of duplex grain size.
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 643, Steels — Micrographic determination of the apparent grain size
ISO 9042, Steels — Point counting method for statistically estimating the volume fraction of a constituent with
a point grid
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:
— — ISO Online browsing platform: available at https://www.iso.org/obp
— — IEC Electropedia: available at https://www.electropedia.org/
3.1 3.1
duplex grain size
condition existent when the distribution of grain intercept lengths, diameters or areas deviates from a single
lognormal distribution
Note 1 to entry: Various types of duplex grain sizes are described in 8.18.1.
3.2 3.2
equivalent diameter
diameter of a circle with an area equivalent to that of the grain
Note 1 to entry: The area is calculated as the geometric mean of the long axis (the maximum chord length) and the short
axis (the maximum chord length perpendicular to the long axis), obtained by multiplying the two axes and taking the
square root of the product.
3.3 3.3
random duplex grain size
grains of two or more significantly different sizes that are randomly distributed
Note 1 to entry: See 5.15.1 for further explanations.
3.4 3.4
topological duplex grain size
grains of two or more significantly different sizes that vary in a non-random, definable pattern
Note 1 to entry: See 5.15.1 for further explanations.
4 Abbreviated terms
The abbreviated terms used are given in Table 1Table 1
Table 1 — Abbreviated terms
Terms Definition
ALA As large as
AGS Apparent grain size
BD Banding
BM Bi Modal
CS Cross section
DG Duplex grain
L Longitudinal
NL Necklace
T Transverse
WR Wide range
G ALA grain size
ALA
G AGS grain size
5 Principle
5.1 5.1 Duplex grain size is classified into two main categories: random duplex grain size and
topological duplex grain size, each with specified subcategories. Random duplex grain size includes: Individual
coarse grains (ALA), Wide range grains (WR) and Bimodal grains (BM). Topological duplex grain size includes:
Cross-section variations of grains (CS), Necklace grains (NL) and Grains in bands (BD). This pattern may be
related to the shape of the product being examined or the factors influencing grain formation. The document
specifies methods for analysing the distribution type, rating the grain size, and estimating the area fractions
occupied by each distinct grain size type. See Figure B.1Figure B.1 in Annex BAnnex B for the
classification procedure for grain size distribution.
5.2 5.2 This document outlines methods for identifying the presence of duplex grain size and
characterizing the features of specific types of duplex grain sizes. It includes procedures for estimating the
area fractions occupied by distinct grain sizes. The document establishes test methods for determining ALA
grain size and provides guidelines for applying ISO 643 to determine grain size in specific designated areas.
Additionally, it offers methods for reporting detailed and distinctive information for each type of duplex grain
size. Furthermore, the test methods provide a statistical procedure for determining the actual distribution of
all grain sizes present in a duplex grain size specimen.
5.3 5.3 The method may be applied to specimens or products containing grains of two or more
significantly different sizes, but distributes at random or in topologically varying patterns.
5.4 5.4 The total specimen surface shall be evaluated when the test method describes deviations from
a single, log-normal distribution of grain sizes and characterizes pattern of variations in grain size.
6 Apparatus
6.1 General
The apparatus used shall depend on the nature of the test method as described in 6.26.2 to 6.46.4.
6.2 Comparison procedure for estimation of area fractions
This procedure shall require the use of comparison charts presented in Annex AAnnex A, Figure A.1, Figure A.1
to improve the accuracy of visual estimates of area fractions occupied by a distinct grain size. These
comparison charts show different area percentages of light grains among dark grains.
6.3 Point count procedure for estimation of area fractions
This procedure shall require the use of a test grid on a transparent overlay, or on a reticle, as specified in ISO
9042.
6.4 Determination of grain size
The devices specified in ISO 643 shall be used. For specimens exhibiting different grain size distributions, the
test methods outlined in ISO 643 — such as the rating chart method, planimetric method, or intercept method
— shall be employed to rate the distinct grain sizes. Additionally, the intercept length method described in ISO
643:2024, Annex E, may also be utilized for this purpose. When rating individual ALA grains, the assessment
shall be based on the equivalent diameter or the area of the maximum grain.
7 Sampling and preparation of test specimens
In order to characterize patterns of duplex grain size the entire cross section of the specimen from the product
shall be evaluated. The examined surface shall be along the longitudinal direction in a plane parallel to the
direction of maximum product deformation except in the case of bars and tubes where the examined surface
shall be perpendicular to the direction of the maximum deformation. The number of test specimens and their
location shall be specified in the relevant product standard. When it is not the case, they are left at the
producer's discretion.
A flat surface of the test specimen shall be polished for micrographic examination and shall be etched for an
adequate period of time by means of the appropriate etching. The etch shall be such that all, or nearly all, of
the grain boundaries are visible.
8 Procedure
8.1 Recognizing and classifying duplex grain size
8.1.1 Random duplex grain size
8.1.1.1 General
A random duplex graimgrain sizes is defined as any of the following.
8.1.1.2 Random coarse grains(ALA)
This is the presence of randomly distributed individual coarse grains, differing in size by three or more ISO
grain size numbers from the average size of the balance of the grains.
These individual coarse grains shall comprise 5 % or less of the area of the specimens. If they comprise more
than 5 % of that area, treat the specimen as described in 8.1.1.48.1.1.4.
An example of a photomicrograph of the ALA condition appears in Figure 1Figure 1.
8.1.1.3 Wide range grains
This is the presence of an unusually wide range of grain sizes, randomly distributed, with the largest size
differing from the smallest size by five or more ISO size numbers.
An example of a photomicrograph of the wide-range condition appears in Figure 2Figure 2.
8.1.1.4 8.1.1.4 Bimodal grains
This is the presence of two distinct grain sizes, randomly distributed such that the sizes differ by more than
four ISO grain size numbers, and such that the two sizes together comprise 75 % or more of the total area of
the specimen.
Two examples of photomicrographs of the bimodal condition appear in Figure 3Figure 3.
8.1.2 Topological duplex grain size
8.1.2.1 General
A topological duplex grain size is defined as any of the following.
8.1.2.2 Cross-section variations of grains
This is the presence of a systematic variation in grain size across the section of the product, such that the
average grain size differs from one area to another by three or more ISO grain size numbers; or the presence
of different grains sizes in specific areas of a product cross-section (e.g.,. coarse grains resulting from
germinative grain growth at areas of critical strains), such that the grain size in those specific areas differs
from the grains size in the bulk of the cross-section by three or more ISO grain size numbers.
An example of a photomicrograph of the cross-section condition appears in Figure 4Figure 4.
8.1.2.3 Necklace grains
This is the presence of individual coarse grains, each surrounded by rings of finer grains, the coarse and fine
grains differing in size by three or more ISO grain size numbers.
Two examples of photomicrographs of the necklace condition appear in Figure 5Figure 5.
8.1.2.4 Grains in bands
This is the presence of bands of distinct grain sizes, such that the sizes differ by three or more ISO grain size
numbers.
Two examples of photomicrographs of the banding condition appear in Figure 6Figure 6.
A mixture of different grain size types is illustrated in Figure 7Figure 7.
Figure 1 — ALA condition
Figure 2 — WR condi
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