ASTM E1382-97(2010)

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

SIGNIFICANCE AND USE
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.
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.  
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.
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:

General Information

• Status: Historical
• Publication Date: 31-Oct-2010
• ICS: 19.120 - Particle size analysis. Sieving
• Technical Committee: E04 - Metallography
• Drafting Committee: E04.14 - Quantitative Metallography

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E1382 − 97(Reapproved 2010)
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.Anumber 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
interceptlengthsorareas,inmetallicandnonmetallicpolycrystallinematerials.Thetestmethodsmay
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
frommeasurementsofgraininterceptlengths,interceptcounts, 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
digitizingtabletorbyautomaticimageanalysisusinganimage
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
boundariescanbeclearlydelineatedbyetchingandsubsequent
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
1.7 The sections appear in the following order: ALA Grain Size 13.9.8
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 Nov. 1, 2010. Published January 2011. Originally
Examples of Proper and Improper Grain Boundary Annex
approved in 1991. Last previous edition approved in 2004 as E1382–97(2004).
Delineation A2
DOI: 10.1520/E1382-97R10.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1382 − 97 (2010)
2. Referenced Documents 3.3 Symbols:
α=the phase of interest for grain size measurement in a
2.1 ASTM Standards:
two-phase (constituent) microstructure.
E3Guide for Preparation of Metallographic Specimens
¯
A =average area of α grains in a two-phase (constituent)
α
E7Terminology Relating to Metallography
microstructure.
E112Test Methods for Determining Average Grain Size
¯
A =area fraction of α grains in a two-phase microstruc-
Aα
E407Practice for Microetching Metals and Alloys
ture.
E562Test 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
E883Guide for Reflected–Light Photomicrography
th
¯
A =mean grain area for the i field.
i
E930Test 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
E1181Test Methods for Characterizing Duplex Grain Sizes
d=diameter of test circle.
E1245Practice for Determining the Inclusion or Second-
G=ASTM grain size number.
Phase Constituent Content of Metals byAutomatic 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
th
3.1 Definitions—For definitions of terms used in these test
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 =grainboundarylengthperunittestareaforthei field.
Ai
th
3.2 Definitions of Terms Specific to This Standard: l =intercept length for the i grain.
i
th
¯
3.2.1 chord (intercept) length—the distance between two l =mean intercept length for the i field.
i
th
opposed, adjacent grain boundary intersection points on a L =length of grain boundaries in the i field.
i
th
straight test line segment that crosses the grain at any location L =true test line or scan line length for the i field.
ti
due to random placement of the test line. L =length of grain edges per unit volume.
v
M=magnification.
3.2.2 graininterceptcount—determinationofthenumberof
n=number of fields measured or the number of grid
times a test line cuts through individual grains on the plane of
placements (or the number of any measurements).
polish (tangent hits are considered as one half an interception).
N=number of grains measured or the number of grain
3.2.3 grain boundary intersection count—determination of
intercepts counted.
the number of times a test line cuts across, or is tangent to,
¯
N =mean number of grains per unit test area for nfields
A
grain boundaries (triple point intersections are considered as
measured.
1 ⁄2 intersections).
th
N =number of grains per unit area for the i field.
Ai
3.2.4 image processing—a generic term covering a variety ¯
N =meannumberof αgrainsinatwo-phasemicrostructure
α
of video techniques that are used to enhance or modify
intercepted by the test lines or scan lines.
contrast, find and enhance edges, clean images, and so forth,
N =number of α grains in a two-phase microstructure
αi
th
prior to measurement.
intercepted by the test lines or scan lines for the i field.
N =number of grains intercepted by the test lines or scan
3.2.5 skeletonization—aniterativeimageamendmentproce-
i
th th
lines for the i field; or, the number of grains counted in the i
dure in which pixels are removed from the periphery of the
field.
grainboundaries(“thinning”),orotherfeatures,unlessremoval
¯
N =mean number of grain intercepts per unit length of test
would produce a loss of connectivity, until each pixel has no
L
lines or scan lines for n fields measured.
more than two nearest neighbors (except at a junction); this is
N =number of grains intercepted per unit length of test
followed by extension of line ends until they meet other line
Li
th
lines or scan lines for the i field.
ends,toconnectmissingorpoorlydelineatedgrainboundaries.
P =numberofgrainboundariesintersectedbythetestlines
i
3.2.6 watershed segmentation—an iterative image amend-
th
or scan lines for the i field.
ment procedure in which each grain, or other features, is
¯
P =mean number of grain boundary intersections per unit
L
eroded to a single pixel, without loosing that pixel (''ultimate
length of test lines or scan lines for nfields measured.
erosion”); this is followed by dilation without touching to
P =numberofgrainboundaryintersectionsperunitlength
Li
rebuild the grain structure with a very thin line (grain bound-
th
of test lines or scan lines for the i field.
aries) separating each grain.
¯
P =point fraction of the α grains in a two-phase micro-
Pα
structure.
s =grain boundary surface area per unit volume.
v
2 ½
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
¯
s=standard deviation=[(1⁄(n−1) ∑ (X −X) ] .
i
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
¯
X=any mean value= ∑ X /n.
Standards volume information, refer to the standard’s Document Summary page on i
the ASTM website. X =any individual measurement.
i
E1382 − 97 (2010)
95% CI=95% confidence interval. 6.2 Etching techniques or etchants that produce only partial
delineation of the grain boundaries will bias test results and
% RA=percent relative accuracy.
must be avoided.
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
graininterceptsorgrainboundaryintersectionsperunitlength,
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
producedbetweenadjacentgrainswithsimilarcontrastorcolor
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
digitizingtabletimageanalyzersorautomaticimageanalyzers. 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,qualityofspecimenpreparation,clarityofthegrain
6.7 Detection of proeutectoid α grains in steels containing
boundaries (etch technique and etchant used), the number of
ferrite and pearlite (and other alloys with similar structures) by
grains measured or the measurement area, errors in detecting
automatic image analyzers can result in detection of ferrite
grainboundariesorgraininteriors,errorsduetodetectingother
within the pearlitic constituent when the interlamellar spacing
features (carbides, inclusions, twin boundaries, and so forth),
is coarse. Use of high magnifications accentuates this problem.
the representativeness of the fields measured, and program-
For such structures, use the lowest possible magnification, or
ming errors.
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
enlargements are used) will bias the test results.
6. Interferences
6.10 Vibrations, if present, can blur the image and bias test
6.1 Improper polishing techniques that leave excessively
results and must be minimized or eliminated when using
large scratches on the surface, or produce excessive deforma-
automatic image analysis.
tion or smearing of the microstructure, or produce pull-outs
and other defects, will lead to measurement errors, particularly 6.11 Dust in the microscope or camera system may produce
when automatic image analyzers are employed. spuriou
...