ASTM E1382-97(2015)
(Test Method)Standard Test Methods for Determining Average Grain Size Using Semiautomatic and Automatic Image Analysis
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 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 and health practices and determine the applicability of regulatory limitations prior to use.
1.7 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...
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Designation: E1382 − 97 (Reapproved 2015)
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
Scope 1
1.1 These test methods are used to determine grain size
Referenced Documents 2
from measurements of grain intercept lengths, intercept counts, Terminology 3
Definitions 3.1
intersection counts, grain boundary length, and grain areas.
Definitions of Terms Specific to This Standard 3.2
Symbols 3.3
1.2 These measurements are made with a semiautomatic
Summary of Test Method 4
digitizing tablet or by automatic image analysis using an image
Significance and Use 5
of the grain structure produced by a microscope.
Interferences 6
Apparatus 7
1.3 These test methods are applicable to any type of grain
Sampling 8
structure or grain size distribution as long as the grain Test Specimens 9
Specimen Preparation 10
boundaries can be clearly delineated by etching and subsequent
Calibration 11
image processing, if necessary.
Procedure:
Semiautomatic Digitizing Tablet 12
1.4 These test methods are applicable to measurement of
Intercept Lengths 12.3
other grain-like microstructures, such as cell structures.
Intercept and Intersection Counts 12.4
Grain Counts 12.5
1.5 This standard deals only with the recommended test
Grain Areas 12.6
methods and nothing in it should be construed as defining or ALA Grain Size 12.6.1
Two-Phase Grain Structures 12.7
establishing limits of acceptability or fitness for purpose of the
Procedure:
materials tested.
Automatic Image Analysis 13
Grain Boundary Length 13.5
1.6 This standard does not purport to address all of the
Intersection Counts 13.6
safety concerns, if any, associated with its use. It is the
Mean Chord (Intercept) Length/Field 13.7.2
responsibility of the user of this standard to establish appro- Individual Chord (Intercept) Lengths 13.7.4
Grain Counts 13.8
priate safety and health practices and determine the applica-
Mean Grain Area/Field 13.9
bility of regulatory limitations prior to use.
Individual Grain Areas 13.9.4
ALA Grain Size 13.9.8
1.7 The sections appear in the following order:
Two-Phase Grain Structures 13.10
Calculation of Results 14
Test Report 15
These test methods are under the jurisdiction of ASTM Committee E04 on
Precision and Bias 16
Metallography and are the direct responsibility of Subcommittee E04.14 on
Grain Size of Non-Equiaxed Grain Structure Annex
Quantitative Metallography.
Specimens A1
Current edition approved Oct. 1, 2015. Published February 2016. Originally
Examples of Proper and Improper Grain Boundary Annex
approved in 1991. Last previous edition approved in 2010 as E1382 – 97(2010).
Delineation A2
DOI: 10.1520/E1382-97R15.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1382 − 97 (2015)
¯
2. Referenced Documents A = average area of α grains in a two-phase (constituent)
α
2 microstructure.
2.1 ASTM Standards:
¯
A = area fraction of α grains in a two-phase microstruc-
Aα
E3 Guide for Preparation of Metallographic Specimens
ture.
E7 Terminology Relating to Metallography
th
A = total area of grains in the i field.
gi
E112 Test Methods for Determining Average Grain Size
th th
A = true area of the i grain; or, the test area of the i field.
E407 Practice for Microetching Metals and Alloys i
th
¯
A = mean grain area for the i field.
E562 Test Method for Determining Volume Fraction by i
A = area of the largest observed grain.
Systematic Manual Point Count
max
th
A = true test area for the i field.
E883 Guide for Reflected–Light Photomicrography
ti
E930 Test Methods for Estimating the Largest Grain Ob- d = diameter of test circle.
served in a Metallographic Section (ALA Grain Size) G = ASTM grain size number.
¯
E1181 Test Methods for Characterizing Duplex Grain Sizes
l = mean lineal intercept length.
¯
E1245 Practice for Determining the Inclusion or Second- l = mean lineal intercept length of the α phase in a
α
Phase Constituent Content of Metals by Automatic Image
two-phase microstructure for n fields measured.
Analysis ¯
l = mean lineal intercept length of the α phase in a
αi
th
two-phase microstructure for the i field.
3. Terminology
L = test line or scan line length.
3.1 Definitions—For definitions of terms used in these test
¯
L = mean grain boundary length per unit test area.
A
th
methods, (feature-specific measurement, field measurement,
L = grain boundary length per unit test area for the i field.
Ai
flicker method, grain size, gray level, and threshold setting), th
l = intercept length for the i grain.
i
see Terminology E7. th
¯
l = mean intercept length for the i field.
i
th
3.2 Definitions of Terms Specific to This Standard:
L = length of grain boundaries in the i field.
i
th
3.2.1 chord (intercept) length—the distance between two
L = true test line or scan line length for the i field.
ti
opposed, adjacent grain boundary intersection points on a
L = length of grain edges per unit volume.
v
straight test line segment that crosses the grain at any location
M = magnification.
due to random placement of the test line.
n = number of fields measured or the number of grid
3.2.2 grain intercept count—determination of the number of placements (or the number of any measurements).
times a test line cuts through individual grains on the plane of
N = number of grains measured or the number of grain
polish (tangent hits are considered as one half an interception). intercepts counted.
¯
N = mean number of grains per unit test area for nfields
3.2.3 grain boundary intersection count—determination of A
measured.
the number of times a test line cuts across, or is tangent to,
th
N = number of grains per unit area for the i field.
grain boundaries (triple point intersections are considered as
Ai
1 ¯
N = mean number of α grains in a two-phase microstructure
1 ⁄2 intersections).
α
intercepted by the test lines or scan lines.
3.2.4 image processing—a generic term covering a variety
N = number of α grains in a two-phase microstructure
αi
of video techniques that are used to enhance or modify
th
intercepted by the test lines or scan lines for the i field.
contrast, find and enhance edges, clean images, and so forth,
N = number of grains intercepted by the test lines or scan
prior to measurement. i
th th
lines for the i field; or, the number of grains counted in the i
3.2.5 skeletonization—an iterative image amendment proce-
field.
dure in which pixels are removed from the periphery of the
¯
N = mean number of grain intercepts per unit length of test
L
grain boundaries (“thinning”), or other features, unless removal
lines or scan lines for n fields measured.
would produce a loss of connectivity, until each pixel has no
N = number of grains intercepted per unit length of test
Li
more than two nearest neighbors (except at a junction); this is
th
lines or scan lines for the i field.
followed by extension of line ends until they meet other line
P = number of grain boundaries intersected by the test lines
i
ends, to connect missing or poorly delineated grain boundaries.
th
or scan lines for the i field.
3.2.6 watershed segmentation—an iterative image amend-
¯
P = mean number of grain boundary intersections per unit
L
ment procedure in which each grain, or other features, is
length of test lines or scan lines for nfields measured.
eroded to a single pixel, without loosing that pixel (''ultimate
P = number of grain boundary intersections per unit length
Li
erosion”); this is followed by dilation without touching to
th
of test lines or scan lines for the i field.
rebuild the grain structure with a very thin line (grain bound-
¯
P = point fraction of the α grains in a two-phase micro-
Pα
aries) separating each grain.
structure.
3.3 Symbols: α = the phase of interest for grain size mea-
s = grain boundary surface area per unit volume.
v
2 ½
surement in a two-phase (constituent) microstructure.
¯
s = standard deviation = [(1 ⁄(n − 1) ∑ (X − X) ] .
i
¯
X = any mean value = ∑ X /n.
i
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
X = any individual measurement.
i
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
95 % CI = 95 % confidence interval.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. % RA = percent relative accuracy.
E1382 − 97 (2015)
4. Summary of Test Methods 6.3 Etching techniques or etchants that reveal annealing
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
accomplished by measuring intercept lengths or areas for a
using these methods should be carefully examined before (or
large number of grains and grouping the results in histogram
after) measurements are made and manually edited, if neces-
fashion; i.e., frequency of occurrence vs. class limit ranges. A sary.
large number of measurements over several fields are required
6.4 Image processing techniques employed to complete
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
be created in the former case, and grain boundaries may not be
5.1 These test methods cover procedures for determining
produced between adjacent grains with similar contrast or color
the mean grain size, and the distribution of grain intercept
in the latter case.
lengths or grain areas, for polycrystalline metals and nonme-
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
be removed from the field before measurements are made.
5.2 The measurements are performed using semiautomatic
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
bias certain measurements, particularly grain intercept lengths
5.3 The precision and relative accuracy of the test results
and grain areas, performed by automatic image analysis and
depend on the representativeness of the specimen or
also measurements made with a digitizing tablet.
specimens, quality of specimen preparation, clarity of the grain
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
use semiautomatic devices.
5.4 Results from these test methods may be used to qualify
6.8 Dust, pieces of tissue paper, oil or water stains, or other
material for shipment in accordance with guidelines agreed
foreign debris on the surface to be examined will bias the
upon between purchaser and manufacturer, to compare differ-
measurement results.
ent manufacturing processes or process variations, or to pro-
vide data for structure-property-behavior studies.
6.9 If photographic images are measured using a digitizing
tablet, uncertainties in the magnification (particularly when
6. Interferences
enlargements are used) will bias the test results.
6.1 Improper polishing techniques that leave excessively
6.10 Vibrations, if present, can blur the image and bias test
large scratches on the surface, or produce excessive deforma-
results and must be minimized or eliminated when using
tion or smearing of the microstructure, or produce pull-outs
automatic image analysis.
and other
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E1382 − 97 (Reapproved 2010) E1382 − 97 (Reapproved 2015)
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
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 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 and health practices and determine the applicability of regulatory
limitations prior to use.
1.7 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
These test methods are under the jurisdiction of ASTM Committee E04 on Metallography and are the direct responsibility of Subcommittee E04.14 on Quantitative
Metallography.
Current edition approved Nov. 1, 2010Oct. 1, 2015. Published January 2011February 2016. Originally approved in 1991. Last previous edition approved in 20042010 as
E1382 – 97(2004).(2010). DOI: 10.1520/E1382-97R10.10.1520/E1382-97R15.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1382 − 97 (2015)
Section Section
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 Annex
Specimens A1
Examples of Proper and Improper Grain Boundary Annex
Delineation A2
2. Referenced Documents
2.1 ASTM Standards:
E3 Guide for Preparation of Metallographic Specimens
E7 Terminology Relating to Metallography
E112 Test Methods for Determining Average Grain Size
E407 Practice for Microetching Metals and Alloys
E562 Test Method for Determining Volume Fraction by Systematic Manual Point Count
E883 Guide for Reflected–Light Photomicrography
E930 Test Methods for Estimating the Largest Grain Observed in a Metallographic Section (ALA Grain Size)
E1181 Test Methods for Characterizing Duplex Grain Sizes
E1245 Practice for Determining the Inclusion or Second-Phase Constituent Content of Metals by Automatic Image Analysis
3. Terminology
3.1 Definitions—For definitions of terms used in these test methods, (feature-specific measurement, field measurement, flicker
method, grain size, gray level, and threshold setting), see Terminology E7.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 chord (intercept) length—the distance between two opposed, adjacent grain boundary intersection points on a straight test
line segment that crosses the grain at any location due to random placement of the test line.
3.2.2 grain intercept count—determination of the number of times a test line cuts through individual grains on the plane of
polish (tangent hits are considered as one half an interception).
3.2.3 grain boundary intersection count—determination of the number of times a test line cuts across, or is tangent to, grain
boundaries (triple point intersections are considered as 1 ⁄2 intersections).
3.2.4 image processing—a generic term covering a variety of video techniques that are used to enhance or modify contrast, find
and enhance edges, clean images, and so forth, prior to measurement.
3.2.5 skeletonization—an iterative image amendment procedure in which pixels are removed from the periphery of the grain
boundaries (“thinning”), or other features, unless removal would produce a loss of connectivity, until each pixel has no more than
two nearest neighbors (except at a junction); this is followed by extension of line ends until they meet other line ends, to connect
missing or poorly delineated grain boundaries.
3.2.6 watershed segmentation—an iterative image amendment procedure in which each grain, or other features, is eroded to a
single pixel, without loosing that pixel (''ultimate erosion”); this is followed by dilation without touching to rebuild the grain
structure with a very thin line (grain boundaries) separating each grain.
3.3 Symbols: α = the phase of interest for grain size measurement in a two-phase (constituent) microstructure.
A¯ = average area of α grains in a two-phase (constituent) microstructure.
α
A¯ = area fraction of α grains in a two-phase microstructure.
Aα
th
A = total area of grains in the i field.
gi
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
E1382 − 97 (2015)
th th
A = true area of the i grain; or, the test area of the i field.
i
th
A¯ = mean grain area for the i field.
i
A = area of the largest observed grain.
max
th
A = true test area for the i field.
ti
d = diameter of test circle.
G = ASTM grain size number.
l¯ = mean lineal intercept length.
l¯ = mean lineal intercept length of the α phase in a two-phase microstructure for n fields measured.
α
th
l¯ = mean lineal intercept length of the α phase in a two-phase microstructure for the i field.
αi
L = test line or scan line length.
L¯ = mean grain boundary length per unit test area.
A
th
L = grain boundary length per unit test area for the i field.
Ai
th
l = intercept length for the i grain.
i
th
l¯ = mean intercept length for the i field.
i
th
L = length of grain boundaries in the i field.
i
th
L = true test line or scan line length for the i field.
ti
L = length of grain edges per unit volume.
v
M = magnification.
n = number of fields measured or the number of grid placements (or the number of any measurements).
N = number of grains measured or the number of grain intercepts counted.
N¯ = mean number of grains per unit test area for nfields measured.
A
th
N = number of grains per unit area for the i field.
Ai
N¯ = mean number of α grains in a two-phase microstructure intercepted by the test lines or scan lines.
α
th
N = number of α grains in a two-phase microstructure intercepted by the test lines or scan lines for the i field.
αi
th th
N = number of grains intercepted by the test lines or scan lines for the i field; or, the number of grains counted in the i field.
i
N¯ = mean number of grain intercepts per unit length of test lines or scan lines for n fields measured.
L
th
N = number of grains intercepted per unit length of test lines or scan lines for the i field.
Li
th
P = number of grain boundaries intersected by the test lines or scan lines for the i field.
i
P¯ = mean number of grain boundary intersections per unit length of test lines or scan lines for nfields measured.
L
th
P = number of grain boundary intersections per unit length of test lines or scan lines for the i field.
Li
P¯ = point fraction of the α grains in a two-phase microstructure.
Pα
s = grain boundary surface area per unit volume.
v
2 ½
s = standard deviation = [(1 ⁄(n − 1) ∑ (X − X¯) ] .
i
X¯ = any mean value = ∑ X /n.
i
X = any individual measurement.
i
95 % CI = 95 % confidence interval.
% RA = percent relative accuracy.
4. Summary of Test Methods
4.1 Determination of the mean grain size is based on measurement of the number of grains per unit area, the length of grain
boundaries in unit area, grain areas, the number of grain intercepts or grain boundary intersections per unit length, or grain intercept
lengths. These measurements are made for a large number of grains, or all of the grains in a given area, within a microscopical
field and then repeated on additional fields to obtain an adequate number of measurements to achieve the desired degree of
statistical precision.
4.2 The distribution of grain intercept lengths or areas is accomplished by measuring intercept lengths or areas for a large
number of grains and grouping the results in histogram fashion; i.e., frequency of occurrence vs. class limit ranges. A large number
of measurements over several fields are required to obtain an adequate description of the distribution.
5. 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
E1382 − 97 (2015)
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.
6. Interferences
6.1 Improper polishing techniques that leave excessively large scratches on the surface, or produce excessive deformation or
smearing of the microstructure, or produce pull-outs and other defects, will lead to measurement errors, particularly when
automatic image analyzers are employed.
6.2 Etching techniques or etchants that produce only partial delineation of the grain boundaries will bias test results and must
be avoided.
6.3 Etching techniques or etchants that reveal annealing twins in certain face-centered cubic metals and alloys usually should
be avoided if the grain size is to be measured by automatic image analyzers. The presence of twin boundaries can be tolerated when
semiautomatic digitizing tablets are utilized but measurement errors are more likely to occur. Etching techniques and etchants that
do not delineate twin boundaries are preferred for these specimens. Discrimination of grain boundaries but not twin boundaries
using image amendment techniques may be possible with some automatic image analyzers. Such techniques may be employed if
the operator can demonstrate their reliability. Each field evaluated using these methods should be carefully examined before (or
after) measurements are made and manually edited, if necessary.
6.4 Image processing techniques employed to complete missing or incompletely developed grain boundaries, or to create grain
boundaries in grain-contrast/color etched specimens, must be used with caution as false boundaries may be created in the former
case, and grain boundaries may not be produced between adjacent grains with similar contrast or color in the latter case.
6.5 Inclusions, carbides, nitrides, and other similar constituents within grains may be detected as grain boundaries when
automatic image analyzers are utilized. These features should be removed from the field before measurements are made.
6.6 Orientation-sensitive etchants should be avoided as some boundaries are deeply etched, others are properly etched, while
some are barely revealed or not revealed at all. Excessively deep etching with such etchants to bring out the fainter boundaries
should not be done because deep etching creates excessive relief (deviation from planar conditions) and will bias certain
measurements, particularly grain intercept lengths and grain areas, performed by automatic image analysis and also measurements
made with a digitizing tablet.
6.7 Detection of proeutectoid α grains in steels containing ferrite and pearlite (and other alloys with similar structures) by
automatic image analyzers can result in detection of ferrite within the pearlitic constituent when the interlamellar spacing is coarse.
Use of high magnifications accentuates this
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