ASTM E1382-97(2023)
(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 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
Relations
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 service@astm.org. 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 shipmen
...
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