ASTM E1245-95

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Designation: E 1245 – 95
AMERICAN SOCIETY FOR TESTING AND MATERIALS
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Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
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 E 1245; 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 (e) 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 E 3 Methods of Preparation of Metallographic Specimens
E 7 Terminology Relating to Metallography
1.1 This practice describes a procedure for obtaining stereo-
E 45 Test Methods for Determining the Inclusion Content
logical measurements that describe basic characteristics of the
of Steel
morphology of indigenous inclusions in steels and other metals
E 768 Practice for Preparing and Evaluating Specimens for
using automatic image analysis. The practice can be applied to
Automatic Inclusion Assessment of Steel
provide such data for any discrete second phase.
NOTE 1—Stereological measurement methods are used in this practice 3. Terminology
to assess the average characteristics of inclusions or other second-phase
3.1 Definitions:
particles on a longitudinal plane-of-polish. This information, by itself,
3.1.1 For definitions of terms used in this practice, see
does not produce a three-dimensional description of these constituents in
Terminology E 7.
space as deformation processes cause rotation and alignment of these
3.2 Definitions of Terms Specific to This Standard:
constituents in a preferred manner. Development of such information
requires measurements on three orthogonal planes and is beyond the scope
3.2.1 detected feature—the oxide, sulfide, or other second-
of this practice.
phase constituent of interest that is isolated for measurement by
adjustment of the threshold setting to its particular range of
1.2 This practice specifically addresses the problem of
gray level.
producing stereological data when the features of the constitu-
3.2.2 exogenous inclusions—those inclusions that arise
ents to be measured make attainment of statistically reliable
from entrapment of foreign matter within the ingot and are
data difficult.
distributed in a nonuniform, unpredictable manner.
1.3 This practice deals only with the recommended test
3.2.3 feature-specific measurements—individual measure-
methods and nothing in it should be construed as defining or
ment of each detected feature in the field of view.
establishing limits of acceptability.
3.2.4 field measurements—simultaneous measurement of all
1.4 The measured values are stated in SI units, which are to
detected features in the field of view.
be regarded as standard. Equivalent inch-pound values are in
3.2.5 flicker method—the procedure of alternating between
parentheses and may be approximate.
the live video image and the detected image while altering the
1.5 This standard does not purport to address all of the
gray-level threshold range to establish the optimum discrimi-
safety concerns, if any, associated with its use. It is the
nation and detection of the inclusions.
responsibility of the user of this standard to establish appro-
3.2.6 gray level—the range of neutral colors between white
priate safety and health practices and determine the applica-
and black on the monitor screen that corresponds to the feature
bility of regulatory limitations prior to use.
to be detected.
2. Referenced Documents
3.2.7 indigenous inclusions—those inclusions that arise
from the natural precipitation of insoluble nonmetallic phases
2.1 ASTM Standards:
during or after solidification (sulfides) or from combination
with the residual oxygen content before or during solidification
This practice is under the jurisdiction of ASTM Committee E-4 on Metallog-
raphy and is the direct responsibility of Subcommittee E04.14 on Quantitative
Metallography.
Current edition approved Jan. 15, 1995. Published March 1995. Originally
published as E 1245 – 88. Last previous edition E 1245 – 89. Annual Book of ASTM Standards, Vol 03.01.
E 1245
(oxides) and are distributed throughout the ingot in a relatively differences compared to each other and the unetched matrix.
predictable manner. Measurements are made based on the nature of the discrimi-
nated picture point elements in the image. These measure-
3.2.8 lot—a unit of material processed at one time and
subjected to similar processing variables. ments are made on each field of view selected. Statistical
evaluation of the measurement data is based on the field-to-
3.2.9 morphology—the shape and size of a microstructural
field or feature-to-feature variability of the measurements.
phase or constituent.
3.2.10 stereological methods—the procedures used to char-
5. Significance and Use
acterize three-dimensional microstructural features based on
5.1 This practice is used to assess the indigenous inclusions
measurements made on two-dimensional sectioning planes.
or second-phase constituents of metals using basic stereologi-
3.2.11 threshold setting—isolation of a range of gray level
cal procedures performed by automatic image analyzers.
values exhibited by one constituent in the microscope field.
5.2 This practice is not suitable for assessing the exogenous
3.3 Symbols:Symbols:
inclusions in steels and other metals. Because of the sporadic,
unpredictable nature of the distribution of exogenous inclu-
¯
A 5 the average area of inclusions or particles, μm . sions, other methods involving complete inspection, for ex-
A 5 the area fraction of the inclusion or constituent.
ample, ultrasonics, must be used to locate their presence. The
A
A 5 the area of the detected feature.
exact nature of the exogenous material can then be determined
i
A 5 the measurement area (field area, mm ).
T by sectioning into the suspect region followed by serial,
H 5 the total projected length in the hot-working
T
step-wise grinding to expose the exogenous matter for identi-
direction of the inclusion or constituent in the
fication and individual measurement. Direct size measurement
field, μm.
rather than application of stereological methods is employed.
¯
L 5 the average length in the hot-working direction
5.3 Because the characteristics of the indigenous inclusion
of the inclusion or constituent, μm.
population vary within a given lot of material due to the
L 5 the true length of scan lines, pixel lines, or grid
T
influence of compositional fluctuations, solidification condi-
lines (number of lines times the length of the
tions and processing, the lot must be sampled statistically to
lines divided by the magnification), mm.
assess its inclusion content. The largest lot sampled is the heat
n 5 the number of fields measured.
lot but smaller lots, for example, the product of an ingot, within
N 5 the number of inclusions or constituents of a
A
the heat may be sampled as a separate lot. The sampling of a
given type per unit area, mm .
given lot must be adequate for the lot size and characteristics.
N 5 the number of inclusions or constituent par-
i
5.4 The practice is suitable for assessment of the indigenous
ticles or the number of feature interceptions, in
inclusions in any steel (or other metal) product regardless of its
the field.
size or shape as long as enough different fields can be measured
N 5 the number of interceptions of inclusions or
L
to obtain reasonable statistical confidence in the data. Because
constituent particles per unit length (mm) of
the specifics of the manufacture of the product do influence the
scan lines, pixel lines, or grid lines.
morphological characteristics of the inclusions, the report
PP 5 the number of detected picture points.
i
should state the relevant manufacturing details, that is, data
PP 5 the total number of picture points in the field
T
regarding the deformation history of the product.
area.
5.5 To compare the inclusion measurement results from
s 5 the standard deviation.
different lots of the same or similar types of steels, or other
V 5 the volume fraction.
V
¯
X 5 the mean of a measurement. metals, a standard sampling scheme should be adopted such as
X 5 an individual measurement. described in Practice E 45.
i
l5 the mean free path (μm) of the inclusion or
5.6 The test measurement procedures are based on the
constituent type perpendicular to the hot-
statistically exact mathematical relationships of stereology for
working direction.
planar surfaces through a three-dimensional object examined
(X 5 the sum of all of a particular measurement over
using reflected light (see Note 1).
n fields.
5.7 The orientation of the sectioning plane relative to the
(X 5 the sum of all of the squares of a particular
hot-working axis of the product will influence test results. In
measurement over n fields.
general, a longitudinally oriented test specimen surface is
95 % CI 5 the 95 % confidence interval.
employed in order to assess the degree of elongation of the
%RA 5 the relative accuracy, %.
malleable (that is, deformable) inclusions.
5.8 Oxide inclusion measurements for cast metals, or for
4. Summary of Practice
wrought sections that are not fully consolidated, may be biased
4.1 The indigenous inclusions or second-phase constituents
by partial or complete detection of fine porosity or mi-
in steels and other metals are viewed with a light microscope
croshrinkage cavities and are not recommended. Sulfides can
or a scanning electron microscope using a suitably prepared
metallographic specimen. The image is detected using a
Vander Voort, G. F., “Image Analysis,” Vol 10, 9th ed., Metals Handbook:
television-type scanner tube (solid-state or tube camera) and
Materials Characterization, ASM, Metals Park, OH, 1986, pp. 309–322.
displayed on a high resolution video monitor. Inclusions are
Underwood, E. E., Quantitative Stereology, Addison-Wesley Publishing Co.,
detected and discriminated based on their gray-level intensity Reading, MA, 1970.
E 1245
be discriminated from such voids in most instances and such staining may occur; very low humidity must also be avoided as
measurements may be performed. static electricity may damage electronic components. Vibra-
5.9 Results of such measurements may be used to qualify tions, if excessive, must be isolated.
material for shipment according to agreed upon guidelines
8. Sampling
between purchaser and manufacturer, for comparison of differ-
8.1 In general, sampling procedures for heat lots or for
ent manufacturing processes or process variations, or to pro-
vide data for structure-property-behavior studies. product lots representing material from a portion of a heat lot
are the same as described in Practice E 45 (Microscopical
6. Interferences
Methods) or as defined by agreements between manufacturers
6.1 Voids in the metal due to solidification, limited hot and users.
ductility, or improper hot working practices may be detected as
8.2 Characterization of the inclusions in a given heat lot, or
oxides because their gray level range is similar to that of a subunit of the heat lot, improves as the number of specimens
oxides.
tested increases. Testing of billet samples from the extreme top
6.2 Exogenous inclusions, if present on the plane-of-polish, and bottom of the ingots (after discards are taken) will define
will be detected as oxides and will bias the measurements of
worst conditions of oxides and sulfides. Specimens taken from
the indigenous oxides. Procedures for handling this situation interior billet locations will be more representative of the bulk
are given in 12.5.9.
of the material. Additionally, the inclusion content will vary
6.3 Improper polishing techniques that leave excessively with the ingot pouring sequence and sampling should test at
large scratches on the surface, or create voids in or around
least the first, middle and last ingot teemed. The same trends
inclusions, or remove part or all of the inclusions, or dissolve are observed in continuously cast steels. Sampling schemes
water-soluble inclusions, or create excessive relief will bias the must be guided by sound engineering judgment, the specific
measurement results. processing parameters, and producer-purchaser agreements.
6.4 Dust, pieces of tissue paper, oil or water stains, or other
9. Test Specimens
foreign debris on the surface to be examined will bias the
measurement results. 9.1 In general, test specimen orientation within the test lot is
the same as described in Practice E 45 (Microscopical Meth-
6.5 If the programming of the movement of the automatic
stage is improper so that the specimen moves out from under ods). The plane-of-polish should be parallel to the hot-working
the objective causing detection of the mount or air (unmounted axis and, most commonly, taken at the quarter-thickness
specimen), measurements will be biased. location. Other test locations may also be sampled, for ex-
6.6 Vibrations must be eliminated if they cause motion in ample, subsurface and center locations, as desired or required.
the image. 9.2 The surface to be polished should be large enough in
6.7 Dust in the microscope or camera system may produce area to permit measurement of at least 100 fields at the
spurious indications that may be detected as inclusions. Con- necessary magnification. Larger surface areas are beneficial
sequently, the imaging system must be kept clean. whenever the product form permits. A minimum polished
2 2
surface area of 160 mm (0.25 in. ) is preferred.
7. Apparatus
9.3 Thin product forms can be sampled by placing a number
7.1 A high quality, research-type reflected light microscope, of longitudinally oriented pieces in the mount so that the
preferably of the upright-type, equipped with bright-field
sampling area is sufficient.
objectives of suitable magnifications, is used to image the
10. Specimen Preparation
microstructure. An inverted microscope or metallograph may
also be used but control of field selection with an automated 10.1 Metallographic specimen preparation must be carefully
stage is more difficult. A scanning electron microscope also controlled to produce acceptable quality surfaces for image
may be used to image the structure. analysis. Guidelines and recommended practices are given in
7.2 A pr
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