ASTM E1382-97(2023)

Standard Test Methods for Determining Average Grain Size Using Semiautomatic and Automatic Image Analysis

SIGNIFICANCE AND USE
5.1 These test methods cover procedures for determining the mean grain size, and the distribution of grain intercept lengths or grain areas, for polycrystalline metals and nonmetallic materials with equiaxed or deformed grain shapes, with uniform or duplex grain size distributions, and for single phase or multiphase grain structures.  
5.2 The measurements are performed using semiautomatic digitizing tablet image analyzers or automatic image analyzers. These devices relieve much of the tedium associated with manual measurements, thus permitting collection of a larger amount of data and more extensive sampling which will produce better statistical definition of the grain size than by manual methods.  
5.3 The precision and relative accuracy of the test results depend on the representativeness of the specimen or specimens, quality of specimen preparation, clarity of the grain boundaries (etch technique and etchant used), the number of grains measured or the measurement area, errors in detecting grain boundaries or grain interiors, errors due to detecting other features (carbides, inclusions, twin boundaries, and so forth), the representativeness of the fields measured, and programming errors.  
5.4 Results from these test methods may be used to qualify material for shipment in accordance with guidelines agreed upon between purchaser and manufacturer, to compare different manufacturing processes or process variations, or to provide data for structure-property-behavior studies.
SCOPE
1.1 These test methods are used to determine grain size from measurements of grain intercept lengths, intercept counts, intersection counts, grain boundary length, and grain areas.  
1.2 These measurements are made with a semiautomatic digitizing tablet or by automatic image analysis using an image of the grain structure produced by a microscope.  
1.3 These test methods are applicable to any type of grain structure or grain size distribution as long as the grain boundaries can be clearly delineated by etching and subsequent image processing, if necessary.  
1.4 These test methods are applicable to measurement of other grain-like microstructures, such as cell structures.  
1.5 This standard deals only with the recommended test methods and nothing in it should be construed as defining or establishing limits of acceptability or fitness for purpose of the materials tested.  
1.6 The sections appear in the following order:    
Section  
Section  
Scope  
1  
Referenced Documents  
2  
Terminology  
3  
Definitions  
3.1  
Definitions of Terms Specific to This Standard  
3.2  
Symbols  
3.3  
Summary of Test Method  
4  
Significance and Use  
5  
Interferences  
6  
Apparatus  
7  
Sampling  
8  
Test Specimens  
9  
Specimen Preparation  
10  
Calibration  
11  
Procedure:  
Semiautomatic Digitizing Tablet  
12  
Intercept Lengths  
12.3  
Intercept and Intersection Counts  
12.4  
Grain Counts  
12.5  
Grain Areas  
12.6  
ALA Grain Size  
12.6.1  
Two-Phase Grain Structures  
12.7  
Procedure:  
Automatic Image Analysis  
13  
Grain Boundary Length  
13.5  
Intersection Counts  
13.6  
Mean Chord (Intercept) Length/Field  
13.7.2  
Individual Chord (Intercept) Lengths  
13.7.4  
Grain Counts  
13.8  
Mean Grain Area/Field  
13.9  
Individual Grain Areas  
13.9.4  
ALA Grain Size  
13.9.8  
Two-Phase Grain Structures  
13.10  
Calculation of Results  
14  
Test Report  
15  
Precision and Bias  
16  
Grain Size of Non-Equiaxed Grain Structure Specimens  
Annex A1  
Examples of Proper and Improper Grain Boundary Delineation  
Annex A2  
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental pra...

General Information

• Status: Published
• Publication Date: 31-Mar-2023
• ICS: 13.300 - Protection against dangerous goods
• Technical Committee: E04 - Metallography
• Drafting Committee: E04.14 - Quantitative Metallography

Relations

• Refers: ASTM E883-11(2024) - Standard Guide for Reflected–Light Photomicrography
• Effective Date: 01-Apr-2024
• Refers: ASTM E407-23 - Standard Practice for Microetching Metals and Alloys
• Effective Date: 01-Nov-2023
• Refers: ASTM E562-19e1 - Standard Test Method for Determining Volume Fraction by Systematic Manual Point Count
• Effective Date: 15-Aug-2019
• Refers: ASTM E883-11(2017) - Standard Guide for Reflected–Light Photomicrography
• Effective Date: 01-Jun-2017
• Refers: ASTM E930-99(2015) - Standard Test Methods for Estimating the Largest Grain Observed in a Metallographic Section (ALA Grain Size)
• Effective Date: 01-Oct-2015
• Refers: ASTM E407-07(2015)e1 - Standard Practice for Microetching Metals and Alloys
• Effective Date: 01-Jun-2015
• Refers: ASTM E7-15 - Standard Terminology Relating to Metallography
• Effective Date: 01-Jun-2015
• Refers: ASTM E7-14 - Standard Terminology Relating to Metallography
• Effective Date: 01-Nov-2014
• Refers: ASTM E112-12 - Standard Test Methods for Determining Average Grain Size
• Effective Date: 15-Nov-2012
• Refers: ASTM E562-08e1 - Standard Test Method for Determining Volume Fraction by Systematic Manual Point Count
• Effective Date: 01-Oct-2011
• Refers: ASTM E562-11 - Standard Test Method for Determining Volume Fraction by Systematic Manual Point Count
• Effective Date: 01-Oct-2011
• Refers: ASTM E883-11 - Standard Guide for Reflected–Light Photomicrography
• Effective Date: 01-May-2011
• Refers: ASTM E112-10 - Standard Test Methods for Determining Average Grain Size
• Effective Date: 01-Nov-2010
• Refers: ASTM E7-03(2009) - Standard Terminology Relating to Metallography
• Effective Date: 01-Oct-2009
• Refers: ASTM E1245-03(2008) - Standard Practice for Determining the Inclusion or Second-Phase Constituent Content of Metals by Automatic Image Analysis
• Effective Date: 01-Oct-2008

Overview

ASTM E1382-97(2023), Standard Test Methods for Determining Average Grain Size Using Semiautomatic and Automatic Image Analysis, is a key international standard developed by ASTM International. It provides quantitative methods to determine average grain size and grain size distribution in polycrystalline materials-including metals and nonmetallic substances-by employing advanced image analysis techniques. The standard addresses both equiaxed and non-equiaxed grain structures, as well as single-phase or multiphase systems, making it highly versatile for metallographic analysis.

These methods utilize semiautomatic digitizing tablets and automatic image analyzers, allowing faster, more accurate, and statistically robust data collection compared to manual grain measurement techniques. The standard is broadly adopted across laboratories and manufacturing environments to ensure quality control, support research, and provide data for material qualification and structure-property investigations.

Key Topics

• Grain Size Measurement: ASTM E1382 prescribes procedures for determining mean grain size based on grain intercept lengths, intercept counts, intersection counts, grain areas, and grain boundary length.
• Image Analysis Methods: The standard describes both semiautomatic (digitizing tablet) and fully automatic (computerized analysis) approaches, utilizing images acquired by optical or electron microscopes.
• Applicability: Methods are valid for various material types and grain structures, including deformed, equiaxed, duplex, and multiphase materials, provided clear grain boundaries are achievable through proper etching and image processing.
• Precision and Accuracy: Addresses variables impacting measurement quality, such as specimen representativeness, etch quality, number of grains measured, and image clarity. Recognizes factors like carbides, inclusions, and twin boundaries as possible sources of interference.
• Statistical Significance: Emphasizes more extensive data sampling to enhance the statistical reliability of grain size analysis versus manual approaches.
• Procedural Guidance: Offers detailed instructions for specimen selection, preparation, etching, calibration, and data reporting to ensure consistency and reproducibility.

Applications

ASTM E1382 is widely used in industries and laboratories requiring precise grain size quantification, with practical applications including:

• Quality Control: Enabling objective qualification of materials before shipment, per purchaser-manufacturer agreements.
• Process Comparison: Assessing and comparing results from different manufacturing processes or process variations to optimize microstructures.
• Materials Research: Supporting structure-property-behavior studies vital to materials development, failure analysis, and product performance improvement.
• Educational and Training Settings: Serving as a reference for teaching advanced metallographic techniques and the practical application of image analysis.
• Metallographic Certification: Supporting compliance in laboratories following recognized standards for metallographic examination and reporting.

Note: Effective usage of ASTM E1382 requires the selection of appropriate sampling locations, meticulous specimen preparation (especially etching for grain boundary delineation), and careful calibration of analytical equipment to ensure measurement accuracy.

Related Standards

ASTM E1382 aligns closely with several other ASTM standards, supporting a comprehensive approach to metallography and quantitative microstructural analysis:

• ASTM E3 – Guide for Preparation of Metallographic Specimens
• ASTM E7 – Terminology Relating to Metallography
• ASTM E112 – Test Methods for Determining Average Grain Size
• ASTM E407 – Practice for Microetching Metals and Alloys
• ASTM E883 – Guide for Reflected-Light Photomicrography
• ASTM E562 – Test Method for Determining Volume Fraction by Systematic Manual Point Count
• ASTM E930 – Estimating the Largest Grain Observed (ALA Grain Size)
• ASTM E1181 – Characterizing Duplex Grain Sizes
• ASTM E1245 – Determining Inclusion or Second-Phase Constituent Content by Automatic Image Analysis

For laboratories and professionals engaged in microstructural characterization, reference to these related documents ensures best practices across all steps-specimen preparation, measurement, and reporting-further supporting robust and standardized grain size analysis.

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Keywords: ASTM E1382, average grain size, image analysis, metallography standard, automatic image analyzer, grain size distribution, materials quality control, microstructural analysis, polycrystalline metals, nonmetallic materials, grain boundary delineation.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E1382 − 97 (Reapproved 2023)
Standard Test Methods for
Determining Average Grain Size Using Semiautomatic and
Automatic Image Analysis
This standard is issued under the fixed designation E1382; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
These test methods may be used to determine the mean grain size, or the distribution of grain
intercept lengths or areas, in metallic and nonmetallic polycrystalline materials. The test methods may
be applied to specimens with equiaxed or elongated grain structures with either uniform or duplex
grain size distributions. Either semiautomatic or automatic image analysis devices may be utilized to
perform the measurements.
1. Scope
Section Section
Summary of Test Method 4
1.1 These test methods are used to determine grain size
Significance and Use 5
from measurements of grain intercept lengths, intercept counts, Interferences 6
Apparatus 7
intersection counts, grain boundary length, and grain areas.
Sampling 8
Test Specimens 9
1.2 These measurements are made with a semiautomatic
Specimen Preparation 10
digitizing tablet or by automatic image analysis using an image
Calibration 11
of the grain structure produced by a microscope.
Procedure:
Semiautomatic Digitizing Tablet 12
1.3 These test methods are applicable to any type of grain
Intercept Lengths 12.3
structure or grain size distribution as long as the grain Intercept and Intersection Counts 12.4
Grain Counts 12.5
boundaries can be clearly delineated by etching and subsequent
Grain Areas 12.6
image processing, if necessary.
ALA Grain Size 12.6.1
Two-Phase Grain Structures 12.7
1.4 These test methods are applicable to measurement of
Procedure:
other grain-like microstructures, such as cell structures.
Automatic Image Analysis 13
Grain Boundary Length 13.5
1.5 This standard deals only with the recommended test
Intersection Counts 13.6
methods and nothing in it should be construed as defining or Mean Chord (Intercept) Length/Field 13.7.2
Individual Chord (Intercept) Lengths 13.7.4
establishing limits of acceptability or fitness for purpose of the
Grain Counts 13.8
materials tested.
Mean Grain Area/Field 13.9
Individual Grain Areas 13.9.4
1.6 The sections appear in the following order:
ALA Grain Size 13.9.8
Two-Phase Grain Structures 13.10
Section Section
Scope 1 Calculation of Results 14
Test Report 15
Referenced Documents 2
Terminology 3 Precision and Bias 16
Grain Size of Non-Equiaxed Grain Structure Annex
Definitions 3.1
Definitions of Terms Specific to This Standard 3.2 Specimens A1
Examples of Proper and Improper Grain Boundary Annex
Symbols 3.3
Delineation A2
1.7 This standard does not purport to address all of the
These test methods are under the jurisdiction of ASTM Committee E04 on
safety concerns, if any, associated with its use. It is the
Metallography and are the direct responsibility of Subcommittee E04.14 on
responsibility of the user of this standard to establish appro-
Quantitative Metallography.
Current edition approved April 1, 2023. Published May 2023. Originally
priate safety, health, and environmental practices and deter-
approved in 1991. Last previous edition approved in 2015 as E1382 – 97(2015).
mine the applicability of regulatory limitations prior to use.
DOI: 10.1520/E1382-97R23.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1382 − 97 (2023)
1.8 This international standard was developed in accor- 3.2.6 watershed segmentation—an iterative image amend-
dance with internationally recognized principles on standard- ment procedure in which each grain, or other features, is
ization established in the Decision on Principles for the
eroded to a single pixel, without loosing that pixel (''ultimate
Development of International Standards, Guides and Recom-
erosion”); this is followed by dilation without touching to
mendations issued by the World Trade Organization Technical
rebuild the grain structure with a very thin line (grain bound-
Barriers to Trade (TBT) Committee.
aries) separating each grain.
3.3 Symbols:
2. Referenced Documents
α = the phase of interest for grain size measurement in a
2.1 ASTM Standards:
two-phase (constituent) microstructure.
E3 Guide for Preparation of Metallographic Specimens
¯
A = average area of α grains in a two-phase (constituent)
α
E7 Terminology Relating to Metallography
microstructure.
E112 Test Methods for Determining Average Grain Size
¯
A = area fraction of α grains in a two-phase microstruc-
Aα
E407 Practice for Microetching Metals and Alloys
ture.
E562 Test Method for Determining Volume Fraction by
th
A = total area of grains in the i field.
gi
Systematic Manual Point Count
th th
A = true area of the i grain; or, the test area of the i field.
i
E883 Guide for Reflected–Light Photomicrography
th
¯
A = mean grain area for the i field.
i
E930 Test Methods for Estimating the Largest Grain Ob-
A = area of the largest observed grain.
max
served in a Metallographic Section (ALA Grain Size)
th
A = true test area for the i field.
ti
E1181 Test Methods for Characterizing Duplex Grain Sizes
d = diameter of test circle.
E1245 Practice for Determining the Inclusion or Second-
G = ASTM grain size number.
Phase Constituent Content of Metals by Automatic Image
¯
l = mean lineal intercept length.
Analysis
¯
l = mean lineal intercept length of the α phase in a
α
two-phase microstructure for n fields measured.
3. Terminology
¯
l = mean lineal intercept length of the α phase in a
αi
3.1 Definitions—For definitions of terms used in these test
th
two-phase microstructure for the i field.
methods, (feature-specific measurement, field measurement,
L = test line or scan line length.
flicker method, grain size, gray level, and threshold setting),
¯
L = mean grain boundary length per unit test area.
A
see Terminology E7.
th
L = grain boundary length per unit test area for the i
Ai
3.2 Definitions of Terms Specific to This Standard:
field.
th
3.2.1 chord (intercept) length—the distance between two
l = intercept length for the i grain.
i
th
opposed, adjacent grain boundary intersection points on a ¯
l = mean intercept length for the i field.
i
th
straight test line segment that crosses the grain at any location
L = length of grain boundaries in the i field.
i
th
due to random placement of the test line.
L = true test line or scan line length for the i field.
ti
3.2.2 grain intercept count—determination of the number of L = length of grain edges per unit volume.
v
times a test line cuts through individual grains on the plane of
M = magnification.
polish (tangent hits are considered as one half an interception).
n = number of fields measured or the number of grid
placements (or the number of any measurements).
3.2.3 grain boundary intersection count—determination of
N = number of grains measured or the number of grain
the number of times a test line cuts across, or is tangent to,
intercepts counted.
grain boundaries (triple point intersections are considered as
¯
N = mean number of grains per unit test area for nfields
1 ⁄2 intersections).
A
measured.
3.2.4 image processing—a generic term covering a variety
th
N = number of grains per unit area for the i field.
Ai
of video techniques that are used to enhance or modify
¯
N = mean number of α grains in a two-phase microstruc-
α
contrast, find and enhance edges, clean images, and so forth,
ture intercepted by the test lines or scan lines
prior to measurement.
N = number of α grains in a two-phase microstructure
αi
3.2.5 skeletonization—an iterative image amendment proce-
th
intercepted by the test lines or scan lines for the i field.
dure in which pixels are removed from the periphery of the
N = number of grains intercepted by the test lines or scan
i
grain boundaries (“thinning”), or other features, unless removal
th th
lines for the i field; or, the number of grains counted in the i
would produce a loss of connectivity, until each pixel has no
field.
more than two nearest neighbors (except at a junction); this is
¯
N = mean number of grain intercepts per unit length of
L
followed by extension of line ends until they meet other line
test lines or scan lines for n fields measured.
ends, to connect missing or poorly delineated grain boundaries.
N = number of grains intercepted per unit length of test
Li
th
lines or scan lines for the i field.
P = number of grain boundaries intersected by the test
i
th
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
lines or scan lines for the i field.
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
¯
P = mean number of grain boundary intersections per unit
Standards volume information, refer to the standard’s Document Summary page on L
the ASTM website. length of test lines or scan lines for nfields measured.
E1382 − 97 (2023)
P = number of grain boundary intersections per unit 6. Interferences
Li
th
length of test lines or scan lines for the i field.
6.1 Improper polishing techniques that leave excessively
¯
P = point fraction of the α grains in a two-phase
Pα
large scratches on the surface, or produce excessive deforma-
microstructure.
tion or smearing of the microstructure, or produce pull-outs
s = grain boundary surface area per unit volume.
v
2 and other defects, will lead to measurement errors, particularly
¯ 1
s = standard deviation = [(1 ⁄(n − 1) ∑ (X − X) ] ⁄2 .
i
when automatic image analyzers are employed.
¯
X = any mean value = ∑ X /n.
i
X = any individual measurement.
6.2 Etching techniques or etchants that produce only partial
i
95 % CI = 95 % confidence interval.
delineation of the grain boundaries will bias test results and
% RA = percent relative accuracy.
must be avoided.
6.3 Etching techniques or etchants that reveal annealing
4. Summary of Test Methods
twins in certain face-centered cubic metals and alloys usually
4.1 Determination of the mean grain size is based on
should be avoided if the grain size is to be measured by
measurement of the number of grains per unit area, the length
automatic image analyzers. The presence of twin boundaries
of grain boundaries in unit area, grain areas, the number of
can be tolerated when semiautomatic digitizing tablets are
grain intercepts or grain boundary intersections per unit length,
utilized but measurement errors are more likely to occur.
or grain intercept lengths. These measurements are made for a
Etching techniques and etchants that do not delineate twin
large number of grains, or all of the grains in a given area,
boundaries are preferred for these specimens. Discrimination
within a microscopical field and then repeated on additional
of grain boundaries but not twin boundaries using image
fields to obtain an adequate number of measurements to
amendment techniques may be possible with some automatic
achieve the desired degree of statistical precision.
image analyzers. Such techniques may be employed if the
4.2 The distribution of grain intercept lengths or areas is operator can demonstrate their reliability. Each field evaluated
using these methods should be carefully examined before (or
accomplished by measuring intercept lengths or areas for a
large number of grains and grouping the results in histogram after) measurements are made and manually edited, if neces-
fashion; that is, frequency of occurrence versus class limit sary.
ranges. A large number of measurements over several fields are
6.4 Image processing techniques employed to complete
required to obtain an adequate description of the distribution.
missing or incompletely developed grain boundaries, or to
create grain boundaries in grain-contrast/color etched
5. Significance and Use
specimens, must be used with caution as false boundaries may
5.1 These test methods cover procedures for determining
be created in the former case, and grain boundaries may not be
the mean grain size, and the distribution of grain intercept
produced between adjacent grains with similar contrast or color
lengths or grain areas, for polycrystalline metals and nonme-
in the latter case.
tallic materials with equiaxed or deformed grain shapes, with
6.5 Inclusions, carbides, nitrides, and other similar constitu-
uniform or duplex grain size distributions, and for single phase
ents within grains may be detected as grain boundaries when
or multiphase grain structures.
automatic image analyzers are utilized. These features should
5.2 The measurements are performed using semiautomatic
be removed from the field before measurements are made.
digitizing tablet image analyzers or automatic image analyzers.
6.6 Orientation-sensitive etchants should be avoided as
These devices relieve much of the tedium associated with
some boundaries are deeply etched, others are properly etched,
manual measurements, thus permitting collection of a larger
while some are barely revealed or not revealed at all. Exces-
amount of data and more extensive sampling which will
sively deep etching with such etchants to bring out the fainter
produce better statistical definition of the grain size than by
boundaries should not be done because deep etching creates
manual methods.
excessive relief (deviation from planar conditions) and will
5.3 The precision and relative accuracy of the test results
bias certain measurements, particularly grain intercept lengths
depend on the representativeness of the specimen or
and grain areas, performed by automatic image analysis and
specimens, quality of specimen preparation, clarity of the grain
also measurements made with a digitizing tablet.
boundaries (etch technique and etchant used), the number of
6.7 Detection of proeutectoid α grains in steels containing
grains measured or the measurement area, errors in detecting
ferrite and pearlite (and other alloys with similar structures) by
grain boundaries or grain interiors, errors due to detecting other
automatic image analyzers can result in detection of ferrite
features (carbides, inclusions, twin boundaries, and so forth),
within the pearlitic constituent when the interlamellar spacing
the representativeness of the fields measured, and program-
is coarse. Use of high magnifications accentuates this problem.
ming errors.
For such structures, use the lowest possible magnification, or
5.4 Results from these test methods may be used to qualify
use semiautomatic devices.
material for shipment in accordance with guidelines agreed
upon between purchaser and manufacturer, to compare differ- 6.8 Dust, pieces of tissue paper, oil or water stains, or other
foreign debris on the surface to be examined will bias the
ent manufacturing processes or process variations, or to pro-
vide data for structure-property-behavior studies. measurement results.
E1382 − 97 (2023)
6.9 If photographic images are measured using a digitizing tomatic digitizing tablet. For counting grain boundary intersec-
tablet, uncertainties in the magnification (particularly when tions or grains intercepted, a circular test grid, such as
enlargements are used) will bias the test results. described in Test Methods E112, may be used. For measuring
intercept lengths, a test grid with a number of equally spaced
6.10 Vibrations, if present, can blur the image and bias test
straight, parallel lines is used.
results and must be minimized or eliminated when using
automatic image analysis. 7.3 An automatic image analyzer with a camera of adequate
sensitivity can be used to detect the grain boundaries, or grain
6.11 Dust in the microscope or camera system may produce
interiors, and make the appropriate measurements.
spurious detail in the image that may be detected as a grain
7.3.1 A programmable automatic stage to control movement
boundary, particularly on automatic image analyzers, and will
in the x and y directions without operator attention may be
bias the test results. Consequently, the imaging system must be
used, but is not mandatory. Use of a programmable stage
kept clean.
prevents bias in field selection.
6.12 Nonuniform illumination can influence feature detec-
7.4 A computer, of suitable capability, is used with either a
tion and thresholding using automatic image analyzers. Prior to
digitizing tablet or automatic image analyzer to store and
analysis, center the light source (as described in the operating
analyze the measurement data. For automatic image analysis,
instructions for the microscope) and adjust the field and
the computer also controls all of the operations except,
aperture diaphragms for best image clarity. Digital correction
perhaps, focusing (automatic focusing is optional).
methods for nonuniform illumination may be used subse-
7.5 A printer is used to output the data and relevant
quently; however, these methods should not be used in lieu of
proper microscope alignment and adjustment. identification/background information in a convenient format.
Graphical data may be produced with either a printer or plotter,
as desired.
7. Apparatus
7.6 This equipment must be housed in a location relatively
7.1 A high quality, research-type reflected light microscope
free of airborne dust, particularly for automatic image analyz-
is most commonly used to image the microstructure (images
ers. High levels of humidity must be avoided as staining of
from electron metallographic instruments may also be used). If
specimen surfaces may occur during, or before, analysis. Very
a digitizing tablet is utilized for the measurements, illumination
low levels of humidity must also be avoided as static electricity
modes other than bright field may be useful for certain
may damage electronic components. Vibrations, if excessive,
specimens. For example, for optically anisotropic materials
must be isolated, particularly for automatic image analysis.
that are difficult to etch, crossed polarized light may be
required to observe the grain structure. Such images exhibit
8. Sampling
grain contrast or color differences between grains rather than
grain boundary delineation. These images, which usually
8.1 Specimens should be selected to represent average
exhibit low light intensities, can be measured using a digitizing
conditions within a heat lot, treatment lot, or product, or to
tablet but may be more difficult to measure with automatic
assess variations anticipated across or along a product or
image analyzers.
component, depending on the nature of the material being
7.1.1 If an automatic image analyzer is employed to perform
tested and the aims of the investigation. Sampling location and
the measurements, an upright-type metallurgical microscope is
frequency should be based upon agreements between manu-
preferred over an inverted microscope due to the greater ease
facturers and users.
in observing the specimen surface with automatic stage move-
8.2 Specimens should not be taken from areas affected by
ment.
shearing, burning or other processes that will alter the grain
7.2 A semiautomatic digitizing tablet with a measurement
structure.
resolution of at least 0.1 mm can be used to measure the grain
size. A variety of approaches can be employed. The simplest is
9. Test Specimens
to fix a photograph (usually an enlargement) to the tablet
9.1 In general, if the grain structure is equiaxed, any
surface and place a suitable grid over the photograph (place-
specimen orientation is acceptable. However, the presence of
ment done without bias), tape down the corners of the grid, and
an equiaxed grain structure in a wrought specimen can only be
use the cursor, fitted with fine cross hairs, to measure the
determined by examination of a plane of polish parallel to the
appropriate features. Alternatively, the grid can be placed on an
deformation axis. Consequently, preparation of longitudinally
eyepiece reticle. The cursor is moved over the tablet surface
oriented specimens, where the plane-of-polish is parallel to the
and the microscopist can see the illuminated cross hairs in the
deformation axis or grain elongation direction, is recom-
cursor through the eyepieces over the field of view and grid
mended.
pattern. A third approach is to transfer the microstructural
image, test grid image and cursor image to a television monitor. 9.2 If the grain structure of a longitudinally oriented speci-
The microscopist moves the cursor across the tablet surface men is equiaxed, then grain size measurements on this plane, or
while watching the monitor to make the appropriate measure- any other, will be equivalent within the statistical precision of
ments. the test method. If the grain structure is not equiaxed but
7.2.1 A variety of test grids, in the form of transparent elongated, then grain size measurements on specimens with
sheets or as eyepiece reticles, may be utilized with a semiau- different orientations will vary. In this case, the grain size must
E1382 − 97 (2023)
be determined on longitudinal, transverse, and planar surfaces, normally required. Practice E407 and Ref (1) list many
or radial and transverse surfaces, depending on the product suitable etchants. A very high degree of grain boundary
shape, and averaged, as described in Annex A1, to obtain the delineation is required.
mean grain size. If directed test lines (rather than random) are
10.7 A greater range of grain structure etchant types may be
used for intercept counts on non-equiaxed grains in plate or
used for grain size measurement with a semiautomatic digitiz-
sheet type specimens, the required measurements can be made
ing tablet. Grain contrast (1) and tint etchants (1,2) are very
using only two principle test planes, rather than all three, due
effective because they generally provide full delineation of the
to the equivalence of test directions, as described in A1.4.3 and
grain structure.
A1.4.4.
10.8 For certain specimens, for example, austenitic stainless
9.3 The surface to be polished should be large enough in
steels, grain boundary delineation can be improved if the
area to permit measurement of at least five fields, preferably
specimen is subjected to a sensitization treatment which
more, at the necessary magnification. In most cases (except for
precipitates carbides at the grain boundaries.
thin sheet or wire specimens), a minimum polished surface
2 2
10.9 Specimens that contain annealing twins are difficult to
area of 160 mm
(0.25 in. ) is adequate.
measure for grain size because the twin boundaries are detected
9.4 Thin product forms can be sampled by placing one or
as well as the grain boundaries. For such specimens, semiau-
more longitudinally oriented (or transverse, if required for
tomatic digitizing tablet measurements are preferred. Certain
non-equiaxed grain structures) pieces in the mount so that the
electrolytic etching techniques, (3,4) as summarized in Ref (1)
sampling area is sufficient. Adjust the stage movement so that
will delineate the grain boundaries but not the twin boundaries
the interface between adjacent specimens is avoided, that is, is
thus permitting use of automatic image analysis.
not in the field of measurement.
10.10 Specimens that have been carburized for grain size
measurement according to the McQuaid-Ehn technique, as
10. Specimen Preparation
described in Test Methods E112, should be etched using a
10.1 Metallographic specimen preparation must be carefully
reagent that darkens the cementite preferentially, such as
controlled to produce acceptable quality surfaces for image
alkaline sodium picrate (see Practice E407, or Ref (1)) or
analysis. Guidelines and recommended practices are given in
Beraha’s sodium molybdate tint etchant. (1, 2) Any cementite
Guide E3.
not present at a grain boundary is ignored, if a digitizing tablet
10.2 The polishing procedure must remove all deformation is used, or deleted from the image prior to measurement, if
automatic image analysis is used.
and damage induced by the cutting and grinding procedure. All
scratches and smearing must be removed, although very fine
10.11 Delineation of prior-austenite grain boundaries in a
scratches from the final polishing step can usually be tolerated.
hardened alloy steel specimen is quite difficult and usually
Scratches from grinding, or from polishing with abrasives
requires considerable experimentation. The nature of the heat
larger than about 1-μm in diameter, must be removed. Exces-
treatment is usually important, particularly the tempering
sive relief, pitting or pullout must be avoided. Specimens must
temperature, if used. Subjecting the specimen to a temper
be carefully cleaned and dried after polishing.
embrittlement cycle may enhance the etch response, but this
treatment is not helpful if the amounts of P, Sn, As, and Sb are
10.3 Specimens to be rated for grain size should be in the
desired heat treated condition representative of the product, for very low. In general, coarse-grained specimens are more easily
etched for prior-austenite grain size. Reference (1) provides
example, solution annealed, annealed, as-quenched, or
quenched and tempered. Other treatment conditions, such as guidance for development of prior-austenite grain boundaries.
In general, it is difficult to reveal the prior-austenite grain
as-hot rolled, as-hot forged, or as-cold drawn, may be tested as
required but it must be recognized that the grain structure for boundaries to the level required for automatic image analysis,
unless the image can be edited successfully prior to
these conditions may not be equiaxed.
measurement, and measurements with a digitizing tablet may
10.4 Mounting of specimens is not always required depend-
be preferable.
ing on their size and shape and the available preparation
equipment; or, if hand polishing is utilized for bulk specimens 10.12 Heat treatments that precipitate a second-phase con-
stituent along the prior-austenite grain boundaries in steel
of convenient size and shape.
specimens may be useful. Again, this technique works best
10.5 The polished surface area for mounted specimens
with relatively coarse-grained steels.
should be somewhat greater than the area required for mea-
surement to avoid edge interferences. Unmounted specimens 10.13 Image signal processing techniques, such as skeleton-
ization (5,6) or watershed segmentation, (6-8) may be used to
generally should have a surface area much larger than required
for measurement to facilitate leveling, if automatic image complete missing grain boundaries or produce grain boundar-
ies in grain contrast etched specimens. However, these tech-
analysis is to be utilized, as described in 12.2.
niques must be used with caution because skeletonization can
10.6 Etching of specimens is a critical step in the prepara-
produce false grain boundaries and watershed segmentation
tion sequence. The choice of the proper etchant depends on the
composition and heat treatment condition of the specimen. For
automatic image analysis, a flat etch condition, that is, where
The boldface numbers in parentheses refer to the list of references at the end of
the grain boundaries appear dark against a light matrix, is this standard.
E1382 − 97 (2023)
may not produce grain boundaries between two adjacent grains 11.8 When a video camera is employed, follow the manu-
with similar color or gray level. Light pen, mouse, or trackball facturer’s recommendation in adjusting the microscope light
editing of images to complete missing grain boundaries before source and setting the correct level of illumination for the
measurement is an acceptable technique, although slow. particular camera used.
11.9 For automatic image analysis measurements, use the
10.14 Photomicrographs may be prepared, as described in
Guide E883, for measurement with a digitizing tablet. If flicker method of switching back-and-forth between the live
enlargements are used, the magnification must be determined video image and the detected image of either the grain
to a precision of 61 % maximum before measurements are boundaries or grain interiors to establish the correct setting of
made. A sufficient number of fields, selected blindly without the gray-level threshold controls, as described in 13.3.
bias, must be photographed at the required magnification to
12. Procedure: Semiautomatic Digitizing Tablet
ensure adequate statistical precision.
12.1 When photomicrographs are used for measurements,
10.15 Annex A2 shows micrographs of a variety of metals
choose the magnification so that at least fifty grains, preferably
and alloys exhibiting properly and improperly etched grain
more, are present, unless the grain structure is extremely
structures with comments concerning their suitability for
coarse. Avoid an excessively high number of grains per
subsequent analysis using either a semiautomatic digitizing
photograph as counting accuracy may be impaired. To mini-
tablet or an automatic image analyzer.
mize operator fatigue, and to ensure measurement accuracy, the
10.16 Annex A1 describes methods for determining the
smallest grain on the photomicrograph should be about 5 mm
grain size of specimens with nonequiaxed grain shapes, as well
in diameter. Take the micrographs at random, that is, without
as procedures for defining the grain anisotropy index (degree of
bias in the field selection, and prepare a sufficient number, at
grain elongation).
least five, to obtain adequate statistical precision. Fix each
micrograph to the tablet surface, for example using masking
11. Calibration and Standardization
tape, to prevent movement during analysis. Drop the measure-
ment grid onto the photograph to prevent placement bias. Tape
11.1 Use a stage micrometer to determine the true linear
the grid corners to the micrograph or tablet surface to prevent
magnification for each objective and eyepiece combination to
be used. movement during measurement.
12.2 When a microscope is used to produce the image of the
11.2 Determine the magnification of photomicrographs by
grain structure for subsequent measurement, using either a
photographing the stage micrometer image and dividing the
semiautomatic or automatic image analyzer, place the speci-
magnified length of the micrometer scale by the true length.
men on the microscope stage so that its surface is perpendicular
11.3 If enlargements are made from photographic negatives,
to the optic axis. With an inverted-type microscope, simply
set up the enlarger using the negative of the micrometer scale
place the specimen face down on the stage plate and hold it in
and determine the magnification of the enlarged micrograph in
place with the stage clamps. With an upright-type microscope,
the same manner as described in paragraph 11.2. Then, make
place the specimen on a slide and level the surface using clay
enlargements of the grain structure images using the same
or plasticene between the specimen and slide. To avoid
enlarger setting. Alternatively, determine the degree of enlarge-
problems with adherent tissue paper, follow the alternate
ment by comparing the size of features on the enlargement to
leveling procedure described in Practice E1245 (Procedure
their size on the contact print. Repeat this process for a number
section).
of features in the image. Determine the average enlargement
12.2.1 The microscope light source should be checked for
factor of the measured features and multiply this value by the
correct alignment and the illumination intensity should be
magnification of the contact print.
adjusted to the level required by the television camera.
11.4 If a video monitor is used with a semiautomatic
12.2.2 When a live microscopical image is used, either with
digitizing tablet, determine the video monitor magnification for
a digitizing tablet, or an automatic image analyzer, field
each objective and projection eyepiece/camera multiplying
selection should be done blindly without bias. Never attempt to
factor combination using a stage micrometer scale.
choose“ typical” or “worst” fields (except for the ALA method,
see 12.6.1) as bias will be introduced. For manual stage
11.5 If an automatic image analyzer is used, determine the
movement, move the x- and y-stage controls without looking at
size of the test area or magnification bar using a stage
the image. If a programmable stage is available, set the stage
micrometer scale for each objective and projection eyepiece/
controls to sample the image in a systematic manner. Measure-
camera multiplying factor combination (consult the manufac-
ment fields should not be overlapped.
turer’s instruction book for the calibration procedure specific to
12.2.3 To obtain a reasonable degree of measurement
the instrument used).
precision, it is not necessary to sample a large number of fields.
11.6 Use a ruler with a millimetre scale to determine the
Generally, from five to twenty fields are adequate (see the
actual length of straight test lines or the diameter of test circles
comments about the number of fields or measurements re-
used as grids.
quired for each type of measurement described in the following
11.7 Use a stage micrometer to measure the length of sections).
straight test lines or the diameter of test circles on eyepiece 12.2.4 Adjust the magnification of the system so that at least
reticles. 50 grains, preferably more (unless the grain structure is
E1382 − 97 (2023)
extremely coarse), are observed through the eyepieces or on boundary surface area per unit volume, S . Hence, because
V
the television monitor. If an excessively high number of grains these methods are based upon two different geometrical char-
are present in the image, measurement precision will be acteristics of the grain structure, minor grain size differences
impaired. For accurate measurement of intercept lengths or may result when the planar grain size is determined using
grain areas, the smallest grains should be at least 5 mm in methods based on L vs. S .
V V
diameter on the television monitor (9) (for a typical 305
12.3 Intercept Length Method:
mm–330 mm (12 in.–13 in.) diameter monitor).
12.3.1 When a digitizing tablet is used to measure grain
NOTE 1—For automatic image analyzers with a pixel density substan- intercept lengths using a template consisting of parallel straight
tially greater than the commonly used 512 × 512 array, grains somewhat
test lines, as described in 12.3.2, measure only the lengths of
smaller than 5 mm in diameter (on the monitor screen) may be measured
the test lines that intersect grains (that is, measure the chord
with reasonable precision. The operator must determine the minimum
distances between successively intersected grain boundaries).
apparent size grain that can be measured with a deviation of no more than
Generally, each test line will begin and end within a grain and
10 % of the diameter or 20 % of the area using test circles or squares of
known size (see Ref. (9) for an example of this procedure).
these partial chords are not measured (see Table 1).
12.3.2 The test grid, consisting of a number of parallel,
12.2.5 When a semiautomatic digitizing tablet is used with
a live microscope image and an eyepiece test grid reticle, select straight test lines with a spacing greater than the apparent mean
grain diameter, should be randomly superimposed over the
the appropriate reticle for measurement and adjust the magni-
fication so that about 50 grains are visible, unless the grain size photographic or live image, without bias, at two or more
orientations to average any anisotropy that may be present. If
is extremely coarse. Counting accuracy will be impaired if the
number of grains visible is excessively high (smaller apparent the grain structure is clearly elongated, four different orienta-
tions with respect to the longitudinal direction, for example, 0°,
size in the field of view).
12.2.6 The grain size measurement methods described in 45°, 90° and 135°, should be used as described in the Appendix
in Test Methods E1181. This procedure should be repeated on
the following paragraphs are those known to produce accurate
each of at least five photomicrographs or live microscope
results with reasonable precision and minimal bias. There may
images, each randomly selected, until at least 500 grain
be other possible methods, or other equivalent procedures, that
intercept lengths (chords) are measured. If the degree of grain
can be used to measure grain size. The operator should evaluate
elongation (grain anisotropy) is of interest, use grid line
the precision and accuracy of such methods on specimens
orientations of 0° and 90° with respect to the deformation
carefully evaluated by one or more of the recommended
direction of the specimen. The degree of grain elongation, or
methods before utilizing an alternate method or procedure. It
anisotropy, is the ratio of the average intercept lengths parallel
should be recognized that slight differences in grain size ratings
to the deformation direction (0°) to the average intercept length
may be obtained using different methods because different
perpendicular to the deformation direction (90°). Annex A1
aspects of the grain structure are being assessed. Also, minor
provides information concerning the measurement of grain size
deviations from equiaxed conditions may accentuate these
and grain anisotropy for non-equiaxed grain structures.
differences. Methods based on the average grain area or the
¯
number of grains per unit area are directly related to the total
12.3.3 The average intercept length, l, is calculated from the
length of grain edges per unit volume, L . Methods based on number of measured values, N, of l using true length units (μm
V i
the mean intercept length or the number of grain boundary
or mm) by dividing the apparent length on the photomicro-
intersections per unit length are directly related to the grain graph or microscope image by the magnification, M.
TABLE 1 Summary of Counting/Measuring Restrictions for Semiautomatic and Automatic Image Analysis Methods
Method Paragraph Measurement Restrictions
Semiautomatic Image Analysis Methods
Intercept Lengths 12.3 l Measure only whole intercept lengths, ignore intercepts that end within a grain.
i
Intercept & Intersection 12.4 P , N No restrictions except for the diameter of a circular test grid; the number of grains
Li Li
Counts per field.
Grain Count 12.5 N Count only whole grains within a known test area.
Ai
Grain Area 12.6.1 Ai Measure areas of whole grains only.
ALA method 12.6.2 A Measure entire area of the largest observed grain section.
max
Two-Phase Methods 12.7.1 l Measure only whole intercept lengths, ignore intercepts that end within a grain.
αi
Two-Phase Methods 12.7.2 A , P No restrictions.
Aα Pα
N
α
Automatic Image Analysis Methods
Grain Boundary Length/ 13.5.1 L No restrictions as long as the field contains a large number of grains.
Ai
Area
Intersection Counts 13.6.1 P No restrictions as long as the field contains a large number of grains.
Li
¯
Intercept Lengths 13.7.1 l , l Measure only whole intercept (chord) lengths, delete grains intersecting the test
i i
area border.
Grain Count 13.8.1 N Count only whole grains within a known test area.
Ai
¯
Grain Areas 13.9.1 A , A Only whole grains should be in the test area.
i i
ALA Method 13.9.9 A Measure the entire area of the largest observed grain section.
max
¯ ¯
Two-Phase Methods 13.10 l ,A Measure only whole intercept (chord) lengths or whole grain areas.
α α
E1382 − 97 (2023)
12.3.4 A histogram of the intercept lengths may be con- counts at the ends of the test lines, this practice is not
structed to determine or illustrate the uniformity of the grain recommended unless half intercepts or intersections can be
intercept lengths and to detect and analyze duplex grain size tallied separately. For such work, follow the counting rules
conditions. The analytical method is described in Test Methods described in Test Methods E112.
E1181, Appendix X2. 12.4.5 With a circular test grid, end counting problems are
eliminated. When counting grain boundary intersections,
12.3.5 Calculate the standard deviation, s, of the individual
which is usually easier, a tangential intersection with a grain
intercept measurements. Most digitizing tables have software
boundary is counted as one intersection. Each grain boundary
programs established for such computations. If the histogram
cut by the test line is also counted as one intersection. Count an
reveals a duplex condition, calculate s for the intercepts within
intersection of the junction of three grains, a “triple point”, as
each region of the distribution curve. To do this, sort the
1 ⁄2 intersections. If the cursor can be programmed to record
intercept lengths in ascending order, separate the data into the
¯
two individual distributions, and compute l and s for the each triple point intersection as 1 ⁄2, count these separately. If
this cannot be done, count every other triple point intersection
intercept lengths in each distribution. Such a computation is
easy to perform if the data can be read into a spreadsheet type twice. If the test line should intersect a junction between four
grains, which occurs rarely, count this intersection twice, that
computer program.
is, as 2 intersections.
12.4 Intercept and Intersection Count Methods:
12.4.6 For each test circle (or concentric circles) placement,
12.4.1 A digitizing table can be used to count the number of
determine P or N by dividing the number of intersections,
Li Li
grain boundary intersections, P , or the number of grains
i
P , or the number of intercepts, N , by the true test line length,
i i
intercepted, N , (the former is preferred) by a circular test grid
i
that is, the true circle circumference, L :
ti
in the same manner as described for manual measurements of
P
i
P and N in Test Methods E112.
P 5 (1)
Li
L
ti
12.4.2 The test grid or reticle should be a circle, or three
circles as described in Test Methods E112. Although any size
or,
circle can be used, as long as the circle is larger than the largest
N
i
grain in the field, relatively small circles are not recommended
N 5 (2)
Li
L
ti
as the efficiency of the analysis is impaired. In general, the
same recommendations as in Test Methods E112 apply, that is, where:
use a test circle or three concentric circles with a total line
πd
L 5 (3)
length of 500 mm. The average number of intercepts or
ti
M
intersections should be about 100, with a minimum of 70 and
for a single circle of diameter d; or,
a maximum of 150 (unless the grain size is too coarse). This
ideal range may not always be achievable depending upon the
πd 1 πd 1 πd
~ ! ~ ! ~ !
1 2 3
L 5 (4)
available magnification steps, and values outside this range ti
M
may be used in such cases (the number of fields measured
for three concentric circles of diameter d , d , and d and
1 2 3
should be changed to achieve the counting total described in
magnification M.
12.4.3). When using an eyepiece reticle, use of a single test
¯ ¯
12.4.7 Next, calculate the mean values P or N , for N fields
L L
circle, of diameter significantly larger than the largest grain, is
measured, or n grid placements.
recommended to minimize operator fatigue. In this case, the
¯
12.4.8 Then, determine the mean lineal intercept length, l:
average number of intercepts or intersections should be at least
25 per circle. 1 1
¯
l 5 5 (5)
12.4.3 Repeat the analysis until at least 500 grain boundary ¯ ¯
P N
L L
intersections or grain interceptions have been counted on five
¯
where l is in μm or mm.
or more randomly selected fields or photomicrographs. If five
12.4.9 Calculate the standard deviation, s, of the individual
photomicrographs are used and one placement per photograph
measurements of P or N .
Li Li
is insufficient to produce at least 500 counts, repeat the
measurements using different regions of the same photomicro-
12.5 Grain Count (Planimetric) Method:
graphs. For example, if the number of counts for the first grid
12.5.1 Grain size may also be determined by the Jeffries
placement on micrograph one is significantly below 100, drop
planimetric procedure using a digitizing tablet and several
the grid on a second region of the micrograph and repeat the
procedures may be used. However, as with manual application
measurement until about 100 counts are obtained per micro-
of the Jeffries method
...