oSIST prEN ISO 643:2023
(Main)Steels - Micrographic determination of the apparent grain size (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)
Jekla - Mikrografsko določevanje navidezne velikosti kristalnih zrn (ISO/DIS 643:2023)
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Standards Content (Sample)
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.
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oSIST prEN ISO 643:2023
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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
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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.
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ii
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PROVIDE SUPPORTING DOCUMENTATION. © ISO 2023
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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
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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
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).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
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 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
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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:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1 Grains
3.1.1
grain
closed polygonal shape with more or less curved sides, which can be revealed on a flat section through
the sample, polished and prepared for micrographic examination
Note 1 to entry: In ISO 4885 grain is defined as “space lattice formed by atoms with regular interstices".
3.1.2
austenitic grain
crystal with a face-centred cubic crystal structure which may, or may not, contain annealing twins
3.1.3
ferritic grain
crystal with a body-centred cubic crystal structure which never contains annealing twins
Note 1 to entry: If pearlite colonies of similar dimensions to those of the ferrite grains are present, the colonies
are then counted as ferrite grains.
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oSIST prEN ISO 643:2023
ISO/DIS 643:2023(E)
3.2 General
3.2.1
index
positive, zero or possibly negative number G which is derived from the mean number m of grains (3.1.1)
2
counted in an area of 1 mm of the section of the specimen
Note 1 to entry: By definition, G = 1 where m = 16; the other indices are obtained by Formula (1).
3.2.2
intercept
N
number of grains (3.1.1) intercepted by a test line, either straight or curved
Note 1 to entry: See Figure 1.
Note 2 to entry: Straight test lines will normally end within a grain. These end segments are counted as 1/2 an
intercept. N is the average of a number of counts of the number of grains intercepted by the test line applied
randomly at various locations. N is divided by the true line length, L usually measured in millimetres, in order
T
to obtain the number of grains intercepted per unit length, N .
L
3.2.3
intersection
P
number of intersection points between grain (3.1.1) boundaries and a test line, either straight or curved
Note 1 to entry: See Figure 2.
Note 2 to entry: P is the average of a number of counts of the number of grain boundaries intersected by the test
line applied randomly at various locations. P is divided by the true line length, L usually measured in
T
millimetres, in order to obtain the number of grain boundary intersections per unit length, P .
L
4 Symbols
The symbols used are given in Table 1.
Table 1 — Symbols
Symbols Definition Value
1
a Mean area of grain in square millimetres
a =
m
A Apparent area of the test figure in square millimetres —
F
1
Mean grain diameter in millimetres d =
d
m
Diameter of the circle on the ground glass screen of the microscope or on
79,8 mm
D a photomicrograph enclosing the image of the reference surface of the
2
(area = 5 000 mm )
specimen
Linear magnification (to be noted as a reference) of the microscopic
g In principle 100
image
G Equivalent index of grain size G = log m – 3
2
g
Conversion factor from linear magnification × g to linear magnification
K
K =
×100
100
l Mean lineal intercept length, generally expressed in millimetres lN==11//P
LL
l Mean lineal intercept length for G = 0, in millimetres 0,313
0
a
The method for designating the direction conforms to ISO 3785.
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oSIST prEN ISO 643:2023
ISO/DIS 643:2023(E)
TTabablele 1 1 ((ccoonnttiinnueuedd))
Symbols Definition Value
L True length of the test line divided by the magnification, in millimetres —
T
m = 2 n
100
(magnification × 100)
Number of grains per square millimetre of specimen surface in the area
m
examined 2
m = 2 K n
g
(magnification × g)
M Number of the closest standard chart picture where g is not 100 —
Total equivalent number of grains examined on the image of diameter D
n —
g
(with a magnification × g)
n Number of grains completely inside the circle of diameter D —
1
n Number of grains intersected by the circle of diameter D —
2
Total equivalent number of grains examined on the image of diameter D
n —
100
(with magnification × 100)
Mean number of grains intercepted per unit length L —
N
N Mean number of grains intercepted per unit length of the line NN= /L
L LT
a
N Number of intercepts per millimetre in the longitudinal direction —
x
a
N Number of intercepts per millimetre in the transverse direction —
y
a
N Number of intercepts per millimetre in the perpendicular direction —
z
Mean number of counts of the number of grain boundaries intersected by
—
P
the test line applied randomly at various locations
Mean number of grain boundary intersections per unit length of
P
PP= /L
L LT
test line
g
Q Correction factor for non-standard magnification Ql=2 og
2
100
a
The method for designating the direction conforms to ISO 3785.
5 Principle
This document is applicable to grain structures that have a normal (Gaussian) size distribution. The
apparent grain size is determined by micrographic examination of appropriately prepared sections of
the specimen.
The following principal methods are available to obtain an index representing the mean value of the
grain size:
a) comparison method using standard charts (see clause 7.2);
b) planimetric method counting grains to determine the mean number of grains per unit area, (see
clause 7.3);
c) intercept method counting the number of grains or grain boundaries along a line of a known length
(see clause 7.4).
All methods give comparable results.
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oSIST prEN ISO 643:2023
ISO/DIS 643:2023(E)
NOTE Intercept, N, counts for a straight line on a single-phase grain structure where the arrows point to 6
intercepts and two line segments ending within grain (2 × 0,5 = 1 N) and N = 7.
Figure 1 — Example of intercept, N
NOTE Intersection, P, counts for a straight test line placed over a single-phase grain structure where the
arrows point to 7 intersection points and P = 7.
Figure 2 — Example of intersection, P
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oSIST prEN ISO 643:2023
ISO/DIS 643:2023(E)
6 Selection and preparation of the specimen
6.1 Test location
If the order, or the standard defining the product, does not specify the number of specimens and the
point at which they are to be taken from the product, these are left to the manufacturer, although it has
been shown that precision of grain size determination increases the higher the number of specimens
assessed. Care shall be taken to ensure that the specimens are representative of the bulk of the product
(i.e. avoid heavily deformed material such as that found at the extreme end of certain products or where
shearing has been used to remove the specimen, etc.). The specimens shall be polished in accordance
with the usual methods.
Unless otherwise stated by the product standard or by agreement with the customer, the polished
surface can be randomly selected for the specimens with equiaxial grains. The polished surface shall
be parallel to the principal axis of deformation in wrought products, for the specimens with deformed
grains.
NOTE Measurements of the grain size on a transverse plane will be biased if the grain shape is not equiaxial.
6.2 Revealing ferritic grain boundaries
The ferritic grains shall be revealed by etching with nital (ethanolic 2 % to 3 % nitric acid solution), or
with another appropriate reagent.
NOTE In this standard, all chemical compositions are indicated in mass %.
6.3 Revealing austenitic and prior-austenitic grain boundaries
6.3.1 General
In the case of steels having a single-phase or dual-phase mainly austenitic structure (delta ferrite
grains in an austenitic matrix) at ambient temperature, the grains shall be revealed by an etching
solution. For single phase austenitic stainless steels, the most commonly used chemical etchants are
glyceregia, Kalling’s reagent (No. 2) and Marble's reagent. The best electrolytic etch for single or two-
phase stainless steels is aqueous 60 % nitric acid at 1,4 V d.c. for 60 s to 120 s, as it reveals the grain
boundaries but not the twin boundaries. Aqueous 10 % oxalic acid, 6 V d.c., up to 60 s, is commonly
used but is less effective than electrolytic 60 % nitric acid.
For other steels, one or other of the methods specified below shall be used depending on the information
required.
— “Bechet-Beaujard” method by etching with aqueous saturated picric acid solution (see A.2).
— “Kohn” method by controlled oxidation (see A.3).
— “McQuaid-Ehn” method by carburization (see A.4).
— grain boundary sensitization method (see A.7).
— other methods specially agreed upon when ordering.
NOTE The first three methods are for prior-austenitic grain boundaries while the others are for austenitic
Mn or austenitic stainless, see Annex A.
If comparative tests are carried out for the different methods, it is essential to use the same heat
treatment conditions. Results may vary considerably from one method to the other.
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oSIST prEN ISO 643:2023
ISO/DIS 643:2023(E)
7 Characterization of grain size
7.1 General
7.1.1 Characterization methods
The apparent grain size can be determined by three micrographic methods: comparison method,
planimetric method and intercept method.
7.1.2 Formulae
The index is defined by Formula (1):
G
m=×82 (1)
This formula may be stated as Formula (2):
Gm=log −3 (2)
2
NOTE An alternative system of grain size definition is known as the ASTM grain size (see C.2).
7.1.3 Measurement uncertainty
In general, the comparison method allows for an accuracy of 0,5; the planimetric and intercept segment
methods allow for an accuracy of 0,1, see Bibliography [4]. For comparison between methods, the
indexes obtained are usually rounded to multiples of 0,5.
Due to the randomness of the spatial position in which each grain is cut through by the sectioning
plane and due to the measurement error, no determination of apparent grain size can be an exact
measurement. Therefore, for planimetric and intercept methods it can be of interest to calculate the
95 % confidence interval of the grain size measurement result and adjust the number of fields inspected
according to the percentage relative accuracy, % RA, of counting corresponding to the uncertainty of
±0,25 grain size units, taking into account that for a symmetric error of G the % RA of the measured
quantity is not symmetric, see Annex D.
The methods described in this standard yield representative results for specimens with a unimodal
grain size distribution. Applying them to specimens with bimodal (or more complex) size distributions
will yield an average value that likely has no meaningful relationship with the various grain populations,
but may still represent the specimen on average. ISO 14520 may be the more appropriate standard for
characterizing these specimens, see Annex E.
7.2 Comparison method
7.2.1 The image examined on the screen (or on a photomicrograph) shall be compared with a series
of standard charts presented in Annex B or overlays (eye-piece graticules designed for grain size
measurement can be used providing these are traceable to national or international standards). The
standard charts at a magnification of × 100 are numbered from 00 to 10 so that their number is equal
to the index G. Using ASTM E 112 images gives substantially the same results as using the comparison
charts of Annex B.
NOTE All standard charts in Annex B are displayed at a magnification of ×100. The different sizes of circles
2 2
are used between 00 to 2,5 (circle of 2 mm ) and 3,0 to 10 (circle of 0,5 mm ).
7.2.2 The standard chart with the grain size closest to that of the examined fields of the specimen can
then be determined. A minimum of three randomly selected fields shall be assessed on each specimen.
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oSIST prEN ISO 643:2023
ISO/DIS 643:2023(E)
7.2.3 Where the magnification g of the image on the screen or photomicrograph is not ×100, the
index G shall be equal to the number M of the closest standard chart, modified as a function of the ratio
of the magnifications, as given by Formula (3):
g
GM=+2log (3)
2
100
7.2.4 Table 2 gives the relationship between the indices for the usual magnifications.
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oSIST prEN ISO 643:2023
ISO/DIS 643:2023(E)
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© ISO 2023 – All rights reserved
Table 2 — Relationship between indices for the usual magnifications
Standard chart no. M 1 1,5 2 2,5 3 3,5 4 4,5 5 5,5 6 6,5 7 7,5 8 8,5 9 9,5 10
Magnification of
the image a
Q Grain size
g
25 −4 −3 −2,5 −2 −1,5 −1 −0,5 0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5 5,5 6
50 −2 −1 −0,5 0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5 5,5 6 6,5 7 7,5 8
100 0 1 1,5 2 2,5 3 3,5 4 4,5 5 5,5 6 6,5 7 7,5 8 8,5 9 9,5 10
200 +2 3 3,5 4 4,5 5 5,5 6 6,5 7 7,5 8 8,5 9 9,5 10 10,5 11 11,5 12
400 +4 5 5,5 6 6,5 7 7,5 8 8,5 9 9,5 10 10,5 11 11,5 12 12,5 13 13,5 14
500 +4,5 5,5 6 6,5 7 7,5 8 8,5 9 9,5 10 10,5 11 11,5 12 12,5 13 13,5 14 14,5
800 +6 7 7,5 8 8,5 9 9,5 10 10,5 11 11,5 12 12,5 13 13,5 14 14,5 15 15,5 16
1 000 +6,5 7,5 8 8,5 9 9,5 10 10,5 11 11,5 12 12,5 13 13,5 14 14,5 15 15,5 16 16,5
a
The values for g = 500 and g = 1 000 are rounded to the nearest multiple of 0,5.
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oSIST prEN ISO 643:2023
ISO/DIS 643:2023(E)
7.2.5 For the comparison method, if the difference between the maximum index and the minimum
index determined is less than 3, compute the test result as the arithmetic mean of the found indices.
If the indices are calculated using Formula (4), the arithmetic mean is to be calculated after the
modification for non-standard magnification. If this condition is not fulfilled, perform an additional
series of at least 6 determinations of the grain size. If the difference between the maximum index and
the minimum index determined in this new series is less than 3, then compute the test result as the
arithmetic mean of the first and second series of determinations altogether. If this latter condition is
not fulfilled, note the spread and a comment on the findings in the final report. For a more elaborate
discussion on specimens of non-unimodal distribution, see Annex E.
The calculated arithmetic mean of indices shall be rounded to the nearest multiple of 0,5.
7.3 Planimetric method
2
7.3.1 Historically a circle measuring 79,8 mm in diameter (A = 5 000 mm ), see Figure 3, was
F
drawn or superimposed over a micrograph or a live image on a ground glass projection screen. The
magnification was then adjusted so that the circular area contained at least 50 grains in order to
minimize the counting error associated with a circular test pattern. The following procedure and
formulae are magnification neutral.
NOTE The circle referenced an apparent size specifically at ×100 magnification as perceived by an operator
at a microscope using ×10 oculars and ×10 objecti
...
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