ASTM E1245-03(2023)

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: E1245 − 03 (Reapproved 2023)
Standard Practice for
Determining the Inclusion or Second-Phase Constituent
Content of Metals by Automatic Image Analysis
This standard is issued under the fixed designation E1245; 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
This practice may be used to produce stereological measurements that describe the amount, number,
size, and spacing of the indigenous inclusions (sulfides and oxides) in steels. The method may also be
applied to assess inclusions in other metals or to assess any discrete second-phase constituent in any
material.
1. Scope 1.6 This international standard was developed in accor-
dance with internationally recognized principles on standard-
1.1 This practice describes a procedure for obtaining stereo-
ization established in the Decision on Principles for the
logical measurements that describe basic characteristics of the
Development of International Standards, Guides and Recom-
morphology of indigenous inclusions in steels and other metals
mendations issued by the World Trade Organization Technical
using automatic image analysis. The practice can be applied to
Barriers to Trade (TBT) Committee.
provide such data for any discrete second phase.
NOTE 1—Stereological measurement methods are used in this practice 2. Referenced Documents
to assess the average characteristics of inclusions or other second-phase
2.1 ASTM Standards:
particles on a longitudinal plane-of-polish. This information, by itself,
E3 Guide for Preparation of Metallographic Specimens
does not produce a three-dimensional description of these constituents in
space as deformation processes cause rotation and alignment of these
E7 Terminology Relating to Metallography
constituents in a preferred manner. Development of such information
E45 Test Methods for Determining the Inclusion Content of
requires measurements on three orthogonal planes and is beyond the scope
Steel
of this practice.
E768 Guide for Preparing and Evaluating Specimens for
1.2 This practice specifically addresses the problem of
Automatic Inclusion Assessment of Steel
producing stereological data when the features of the constitu-
ents to be measured make attainment of statistically reliable
3. Terminology
data difficult.
3.1 Definitions:
1.3 This practice deals only with the recommended test
3.1.1 For definitions of terms used in this practice, see
methods and nothing in it should be construed as defining or Terminology E7.
establishing limits of acceptability.
3.2 Symbols:
1.4 The values stated in SI units are to be regarded as 2
¯
A = the average area of inclusions or particles, μm .
standard. No other units of measurement are included in this
A = the area fraction of the inclusion or constituent.
A
standard.
A = the area of the detected feature.
i
1.5 This standard does not purport to address all of the A = the measurement area (field area, mm ).
T
H = the total projected length in the hot-working
safety concerns, if any, associated with its use. It is the
T
direction of the inclusion or constituent in the
responsibility of the user of this standard to establish appro-
field, μm.
priate safety, health, and environmental practices and deter-
¯
L = the average length in the hot-working direction
mine the applicability of regulatory limitations prior to use.
of the inclusion or constituent, μm.
This practice is under the jurisdiction of ASTM Committee E04 on Metallog-
raphy and is the direct responsibility of Subcommittee E04.14 on Quantitative
Metallography. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved April 1, 2023. Published April 2023. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1988. Last previous edition approved in 2016 as E1245 – 03(2016). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/E1245-03R23. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1245 − 03 (2023)
example, ultrasonics, must be used to locate their presence.
L = the true length of scan lines, pixel lines, or grid
T
The exact nature of the exogenous material can then be
lines (number of lines times the length of the
determined by sectioning into the suspect region followed by
lines divided by the magnification), mm.
serial, step-wise grinding to expose the exogenous matter for
n = the number of fields measured.
identification and individual measurement. Direct size mea-
N = the number of inclusions or constituents of a
A
given type per unit area, mm . surement rather than application of stereological methods is
N = the number of inclusions or constituent particles employed.
i
or the number of feature interceptions, in the
5.3 Because the characteristics of the indigenous inclusion
field.
population vary within a given lot of material due to the
N = the number of interceptions of inclusions or
L
influence of compositional fluctuations, solidification condi-
constituent particles per unit length (mm) of scan
tions and processing, the lot must be sampled statistically to
lines, pixel lines, or grid lines.
assess its inclusion content. The largest lot sampled is the heat
PP = the number of detected picture points.
i
lot but smaller lots, for example, the product of an ingot, within
PP = the total number of picture points in the field
T
the heat may be sampled as a separate lot. The sampling of a
area.
given lot must be adequate for the lot size and characteristics.
s = the standard deviation.
t = a multiplier related to the number of fields 5.4 The practice is suitable for assessment of the indigenous
examined and used in conjunction with the
inclusions in any steel (or other metal) product regardless of its
standard deviation of the measurements to deter- size or shape as long as enough different fields can be measured
mine the 95 % CI
to obtain reasonable statistical confidence in the data. Because
V = the volume fraction.
the specifics of the manufacture of the product do influence the
V
¯
X = the mean of a measurement.
morphological characteristics of the inclusions, the report
X = an individual measurement.
i should state the relevant manufacturing details, that is, data
λ = the mean free path (μm) of the inclusion or
regarding the deformation history of the product.
constituent type perpendicular to the hot-
5.5 To compare the inclusion measurement results from
working direction.
different lots of the same or similar types of steels, or other
∑X = the sum of all of a particular measurement over
metals, a standard sampling scheme should be adopted such as
n fields.
described in Test Methods E45.
∑X = the sum of all of the squares of a particular
measurement over n fields.
5.6 The test measurement procedures are based on the
95 % CI = the 95 % confidence interval.
statistically exact mathematical relationships of stereology for
% RA = the relative accuracy, %.
planar surfaces through a three-dimensional object examined
using reflected light (see Note 1).
4. Summary of Practice
5.7 The orientation of the sectioning plane relative to the
4.1 The indigenous inclusions or second-phase constituents
hot-working axis of the product will influence test results. In
in steels and other metals are viewed with a light microscope
general, a longitudinally oriented test specimen surface is
or a scanning electron microscope using a suitably prepared
employed in order to assess the degree of elongation of the
metallographic specimen. The image is detected using a
malleable (that is, deformable) inclusions.
television-type scanner tube (solid-state or tube camera) and
5.8 Oxide inclusion measurements for cast metals, or for
displayed on a high resolution video monitor. Inclusions are
wrought sections that are not fully consolidated, may be biased
detected and discriminated based on their gray-level intensity
by partial or complete detection of fine porosity or mi-
differences compared to each other and the unetched matrix.
croshrinkage cavities and are not recommended. Sulfides can
Measurements are made based on the nature of the discrimi-
be discriminated from such voids in most instances and such
nated picture point elements in the image. These measure-
measurements may be performed.
ments are made on each field of view selected. Statistical
evaluation of the measurement data is based on the field-to-
5.9 Results of such measurements may be used to qualify
field or feature-to-feature variability of the measurements.
material for shipment according to agreed upon guidelines
between purchaser and manufacturer, for comparison of differ-
5. Significance and Use
ent manufacturing processes or process variations, or to pro-
5.1 This practice is used to assess the indigenous inclusions
vide data for structure-property-behavior studies.
or second-phase constituents of metals using basic stereologi-
6. Interferences
cal procedures performed by automatic image analyzers.
6.1 Voids in the metal due to solidification, limited hot
5.2 This practice is not suitable for assessing the exogenous
ductility, or improper hot working practices may be detected as
inclusions in steels and other metals. Because of the sporadic,
oxides because their gray level range is similar to that of
unpredictable nature of the distribution of exogenous
oxides.
inclusions, other methods involving complete inspection, for
3 4
Vander Voort, G. F., “Image Analysis,” Vol 10, 9th ed., Metals Handbook: Underwood, E. E., Quantitative Stereology, Addison-Wesley Publishing Co.,
Materials Characterization, ASM, Metals Park, OH, 1986, pp. 309–322. Reading, MA, 1970.
E1245 − 03 (2023)
6.2 Exogenous inclusions, if present on the plane-of-polish, 8. Sampling
will be detected as oxides and will bias the measurements of
8.1 In general, sampling procedures for heat lots or for
the indigenous oxides. Procedures for handling this situation
product lots representing material from a portion of a heat lot
are given in 12.5.9.
are the same as described in Test Methods E45 (Microscopical
Methods) or as defined by agreements between manufacturers
6.3 Improper polishing techniques that leave excessively
and users.
large scratches on the surface, or create voids in or around
inclusions, or remove part or all of the inclusions, or dissolve
8.2 Characterization of the inclusions in a given heat lot, or
water-soluble inclusions, or create excessive relief will bias the
a subunit of the heat lot, improves as the number of specimens
measurement results.
tested increases. Testing of billet samples from the extreme top
and bottom of the ingots (after discards are taken) will define
6.4 Dust, pieces of tissue paper, oil or water stains, or other
worst conditions of oxides and sulfides. Specimens taken from
foreign debris on the surface to be examined will bias the
interior billet locations will be more representative of the bulk
measurement results.
of the material. Additionally, the inclusion content will vary
6.5 If the programming of the movement of the automatic
with the ingot pouring sequence and sampling should test at
stage is improper so that the specimen moves out from under
least the first, middle and last ingot teemed. The same trends
the objective causing detection of the mount or air (unmounted
are observed in continuously cast steels. Sampling schemes
specimen), measurements will be biased.
must be guided by sound engineering judgment, the specific
processing parameters, and producer-purchaser agreements.
6.6 Vibrations must be eliminated if they cause motion in
the image.
9. Test Specimens
6.7 Dust in the microscope or camera system may produce
9.1 In general, test specimen orientation within the test lot is
spurious indications that may be detected as inclusions.
the same as described in Test Methods E45 (Microscopical
Consequently, the imaging system must be kept clean.
Methods). The plane-of-polish should be parallel to the hot-
working axis and, most commonly, taken at the quarter-
7. Apparatus
thickness location. Other test locations may also be sampled,
for example, subsurface and center locations, as desired or
7.1 A reflected light microscope equipped with bright-field
objectives of suitable magnifications is used to image the required.
microstructure. The use of upright-type microscope allows for
9.2 The surface to be polished should be large enough in
easier stage control when selecting field areas; however, the
area to permit measurement of at least 100 fields at the
specimens will require leveling which can create artifacts, such
necessary magnification. Larger surface areas are beneficial
as scratches, dust remnants and staining, on the polished
whenever the product form permits. A minimum polished
surface (see 12.2.1). The use of inverted microscopes usually
surface area of 160 mm is preferred.
result in a more consistent focus between fields, thereby,
9.3 Thin product forms can be sampled by placing a number
requiring less focussing between fields and a more rapid
of longitudinally oriented pieces in the mount so that the
completion of the procedure. A scanning electron microscope
sampling area is sufficient.
also may be used to image the structure.
9.4 Guide E768 lists two accepted methods for preparing
7.2 A programmable automatic stage to control movement
steel samples for the examination of inclusion content using
in the x and y directions without operator attention is recom-
image analysis. The standard also lists a procedure to test the
mended (but not mandatory) to prevent bias in field selection
quality of the preparation using differential interference con-
and to minimize operator fatigue.
trast (DIC).
7.3 An automatic focus device may also be employed if
10. Specimen Preparation
found to be reliable. Such devices may be unreliable when
testing steels or metals with very low inclusion contents.
10.1 Metallographic specimen preparation must be carefully
controlled to produce acceptable quality surfaces for image
7.4 An automatic image analyzer with a camera of adequate
analysis. Guidelines and recommended practices are given in
sensitivity is employed to detect the inclusions, perform
Guides E3, E768, and Test Methods E45.
discrimination, and make measurements.
10.2 The polishing procedure must not alter the true appear-
7.5 A computer is used to store and analyze the measure-
ance of the inclusions on the plane-of-polish by producing
ment data.
excessive relief, pitting, cracking or pullout. Minor fine
7.6 A printer is used to output the data and relevant
scratches, such as from a 1 μm diamond abrasive, do not
identification/background information in a convenient format.
usually interfere with inclusion detection but heavier scratches
are to be avoided. Proper cleaning of the specimen is necessary.
7.7 This equipment must be housed in a location relatively
Use of automatic grinding and polishing devices is recom-
free of airborne dust. High humidity must be avoided as
mended.
staining may occur; very low humidity must also be avoided as
static electricity may damage electronic components. 10.3 Establishment of polishing practices should be guided
Vibrations, if excessive, must be isolated. by Guide E768.
E1245 − 03 (2023)
10.4 Inclusion retention is generally easier to accomplish if surface area substantially greater than required for
specimens are hardened. If inclusion retention is inadequate measurement, the ring form can rest on the outer edges of the
with annealed, normalized, or low hardness as-rolled specimen during leveling and thus not affect the measurement
specimens, they should be subjected to a standard heat treat- area. Some upright-type microscopes can be equipped with an
ment (hardening) cycle, appropriate for the grade. Because autoleveling stage for mounted specimens.
inclusion retention and cracking at carbides may be a problem
12.1.2 For an image analyzer that uses the TV-raster lines to
for certain steels in the as-quenched condition, tempering is
make intercept counts, align the specimen on the stage so that
recommended; generally, a low tempering temperature, for
the longitudinal direction is parallel to the y direction of the
example, 200 °C–260 °C, is adequate.
stage and the inclusions are oriented vertically on the monitor
screen. For a software-based system, the longitudinal direction
10.5 Mounting of specimens is not always required depend-
of the specimen may be oriented parallel to either the xor y axis
ing on their size and shape and the available equipment; or, if
of the stage.
hand polishing is utilized for bulk specimens of convenient size
12.1.3 The microscope light source should be checked for
and shape.
correct alignment and the illumination intensity should be
10.6 The polished surface area for mounted specimens
adjusted to the level required by the television scanner tube.
should be somewhat greater than the area required for mea-
12.1.4 Adjust the magnification of the system to provide
surement to avoid edge interferences. Unmounted specimens
adequate resolution of the inclusions with the largest possible
generally should have a surface area much greater than
field size. Choice of the optimum magnification is a compro-
required for measurement to facilitate leveling using the
mise between resolution and field-to-field measurement vari-
procedure described in 12.1.1.
ability. Higher magnification objectives have higher numerical
10.7 Etching of specimens is not desired for inclusion
aperture ratings and provide improved resolution. However, as
assessment.
magnification increases, the field-to-field measurement vari-
ability increases, which increases the standard deviation of the
11. Calibration and Standardization
measurement. Also, as the magnification increases, the field
11.1 Use a stage micrometer to determine the size of the
area decreases. For example, if the magnification is doubled,
frame to calibrate the image analyzer and to determine the
four times as many fields must be measured to cover the same
overall magnification of the system for each objective.
test area. In general, the lower the inclusion content, the higher
the required magnification, and vice-versa. Intermediate mag-
11.2 Follow the manufacturer’s recommendations in adjust-
nification objectives (for example, 32×, 40×, 50×, 60×, and
ing the microscope light source and setting the correct level of
80×) provide the best combination of resolution and field area.
illumination for the television pick-up camera.
Avoid use of lower magnification objectives that will not
11.3 The flicker method of switching back and forth be-
permit detection of the smaller inclusions. Use the same
tween the inclusion image and the detected image is recom-
objective for all measurements of specimens within a lot. It is
mended to establish the correct setting of the gray-level
recommended that the same objective be used for all measure-
threshold controls as described in 12.2.1. Inspection of the gray
ments of specimens with the same level of inclusion content,
level histogram of the microstructure can be used to define the
for example, 32× to 50× objectives for grades with large
gray level range and threshold settings for the inclusion or
amounts of inclusions, such as free-machining grades, and 50×
constituent types (see 12.2.1). These settings are verified by the
to 80× objectives for vacuum degassed, ladle-refined, or
flicker method.
double-melt grades.
12.1.5 Select the optimum magnification and adjust the light
12. Procedure
source for best resolution. If necessary, enable the shading
12.1 Setting Up the Microscope:
correction adjustment for chosen objective.
12.1.1 Place the specimen on the microscope stage so that
12.2 Setting the Densitometer:
the specimen surface is perpendicular to the optic axis. With an
inverted-type microscope, simply place the polished face down 12.2.1 Gray-level threshold settings are selected to permit
on the stage plate and hold it in place with the stage clamps. independent detection of sulfides and oxides, or a specific
With an upright-type microscope, place the specimen on a slide discrete second phase, using the “flicker method” of switching
and level the surface using clay or plasticene between the back and forth between the inclusion image and the thresh-
specimen and slide. If tissue paper is placed between the olded image. The threshold limits are set for the oxides and the
specimen surface and the ram of the leveling press, small sulfides so that the inclusions are detected without enlargement
pieces of tissue paper may adhere to the surface during of the larger inclusions. In some instances, the threshold
flattening and produce artifacts that affect measurements. In settings may require a minor compromise between detection of
some cases, adherent tissue paper can be blown off the the smallest inclusions and over-detection of the largest inclu-
specimen surface. An alternative leveling procedure to avoid sions. The chosen threshold settings should be tried on inclu-
this problem is to place an aluminum or stainless steel ring sions in a number of fields before beginning the analysis. The
form of appropriate diameter, that has been flattened slightly in threshold range for oxides is close to the black end of the
a vise to an oval shape, between the specimen and the ram. If reflectance scale while the range for sulfides is somewhat
the specimen was mounted, the ring form will rest only on the higher. An alternate approach to establish the threshold settings
surface of the mount. If the specimen is unmounted but with a is to develop a gray-level reflectance histogram of the inclusion
E1245 − 03 (2023)
or constituent types present, as well as the matrix (usu
...