ASTM E1268-19

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Designation: E1268 − 18 E1268 − 19
Standard Practice for
Assessing the Degree of Banding or Orientation of
Microstructures
This standard is issued under the fixed designation E1268; 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
Segregation occurs during the dendritic solidification of metals and alloys and is aligned by
subsequent deformation. Solid-state transformations may be influenced by the resulting microsegre-
gation pattern leading to development of a layered or banded microstructure. The most common
example of banding is the layered ferrite-pearlite structure of wrought low-carbon and low-carbon
alloy steels. Other examples of banding include carbide banding in hypereutectoid tool steels and
martensite banding in heat-treated alloy steels. This practice covers procedures to describe the
appearance of banded structures, procedures for characterizing the extent of banding, and a
microindentation hardness procedure for determining the difference in hardness between bands in heat
treated specimens. The stereological methods may also be used to characterize non-banded
microstructures with second phase constituents oriented (elongated) in varying degrees in the
deformation direction.
1. Scope
1.1 This practice describes a procedure to qualitatively describe the nature of banded or oriented microstructures based on the
morphological appearance of the microstructure.
1.2 This practice describes stereological procedures for quantitative measurement of the degree of microstructural banding or
orientation.
NOTE 1—Although stereological measurement methods are used to assess the degree of banding or alignment, the measurements are only made on
planes parallel to the deformation direction (that is, a longitudinal plane) and the three-dimensional characteristics of the banding or alignment are not
evaluated.
1.3 This practice describes a microindentation hardness test procedure for assessing the magnitude of the hardness differences
present in banded heat-treated steels. For fully martensitic carbon and alloy steels (0.10–0.65 %C), in the as-quenched condition,
the carbon content of the matrix and segregate may be estimated from the microindentation hardness values.
1.4 This standardpractice does not cover chemical analytical methods for evaluating banded structures.
1.5 This practice deals only with the recommended test methods and nothing in it should be construed as defining or establishing
limits of acceptability.
1.6 The measured values are stated in SI units, which are regarded as standard. Equivalent inch-pound values, when listed, are
in parentheses and may be approximate.
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 practices and determine the applicability of
regulatory limitations prior to use.
1.8 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.
This practice is under the jurisdiction of ASTM Committee E04 on Metallography and is the direct responsibility of Subcommittee E04.14 on Quantitative Metallography.
Current edition approved June 1, 2018June 1, 2019. Published March 2019July 2019. Originally approved in 1988. Last previous edition approved in 20162018 as
E1268 – 01E1268 – 18.(2016). DOI: 10.1520/E1268-1810.1520/E1268-19
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1268 − 19
2. Referenced Documents
2.1 ASTM Standards:
A370 Test Methods and Definitions for Mechanical Testing of Steel Products
E3 Guide for Preparation of Metallographic Specimens
E7 Terminology Relating to Metallography
E140 Hardness Conversion Tables for Metals Relationship Among Brinell Hardness, Vickers Hardness, Rockwell Hardness,
Superficial Hardness, Knoop Hardness, Scleroscope Hardness, and Leeb Hardness
E384 Test Method for Microindentation Hardness of Materials
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
3. Terminology
3.1 Definitions—For definitions of terms used in this practice, see Terminology E7.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 banded microstructure—separation, of one or more phases or constituents in a two-phase or multiphase microstructure,
or of segregated regions in a single phase or constituent microstructure, into distinct layers parallel to the deformation axis due
to elongation of microsegregation; other factors may also influence band formation, for example, the hot working finishing
temperature, the degree of hot- or cold-work reduction, or split transformations due to limited hardenability or insufficient quench
rate.
3.2.2 feature interceptions—the number of particles (or clusters of particles) of a phase or constituent of interest that are crossed
by the lines of a test grid. (see Fig. 1).
3.2.3 feature intersections—the number of boundaries between the matrix phase and the phase or constituent of interest that are
crossed by the lines of a test grid (see Fig. 1). For isolated particles in a matrix, the number of feature intersections will equal twice
the number of feature interceptions.
3.2.4 oriented constituents—one or more second-phases (constituents) elongated in a non-banded (that is, random distribution)
manner parallel to the deformation axis; the degree of elongation varies with the size and deformability of the phase or constituent
and the degree of hot- or cold-work reduction.
3.2.5 stereological methods—procedures used to characterize three-dimensional microstructural features based on measure-
ments made on two-dimensional sectioning planes.
3,4
NOTE 2—Microstructural examples are presented in Annex A1 that illustrate a quantitative method to assess the degree of banding (BR).(BR) . The
degree of banding varies: BR<1.3 - no banding; BR >1.9 - one or two solid bands across the whole field of view and several broken bands; BR>2.6 -
several solid bands intersecting the whole field of view; BR>4 and BR>5 - uniform and non-uniform solid bands alternately intersecting the whole field
of view. Fig. 2 describes this classification using a qualitative description of the nature and extent of the banding or orientation of microstructures.
3.3 Symbols:
N = number of feature interceptions with test lines perpendicular to the deformation direction.
'
N = number of feature interceptions with test lines parallel to the deformation direction.
||
P = number of feature boundary intersections with test lines perpendicular to the deformation direction.
'
P = number of feature boundary intersections with test lines parallel to the deformation direction.
||
L = summarized length of feature interceptions by a single test line, parallel to the deformation direction (mm)
||
L = summarized length of feature interceptions by a single test line, parallel to the deformation direction (mm).
||
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.
Lépine, M., “Image Convolutions and their Application to Quantitative Metallography,” Microstructural Science, Vol. 17, Image Analysis and Metallography, ASM
International, Metals Park, OH, 1989, pp. 103–114.Kazakov A., Kiselev D., Andreeva S., Chigintsev L., Golovin S., Egorov V., and Markov S., “Development of a procedure
for the quantitative estimation of microstructural banding of low-alloyed pipeline steels using an automatic image analyzer ,” Chernye metally, 2007, No. 7-8, pp. 31-37.
Fowler, D.B., “A Method for Evaluating Plasma Spray Coating Porosity Content Using Stereological Data Collected by Automatic Image Analysis,” Microstructural
Science, Vol. 18, Computer-Aided Microscopy and Metallography, ASM International, Materials Park, OH, 1990, pp. 13–21.Kazakov, A., Kiselev, D., Kazakova, E., Vander
Voort, G. F., and Chigintsev, L., “Quantitative Description of Microstructural Banding in Steels,” Materials Performance and Characterization, Vol. 6, No. 3, 2017, pp.
224-236, https://doi.org/10.1520/MPC20160009.
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NOTE 1—The test grid lines have been shown oriented perpendicular (A, C) to the deformation axis and parallel (B, D) to the deformation axis. The
counts for N , N , P , P , L , and L are shown for counts made from top to bottom (A, C) or from left to right (B, D).
' || ' || ' ||
NOTE 2—T indicates a tangent hit and E indicates that the grid line ended within the particle; both situations are handled as shown.
NOTE 3—L indicates full length of a test grid line.
t
FIG. 1 Illustration of the Counting of Particle Interceptions (N) and Boundary Intersections (P) for an Oriented Microstructure
E1268 − 19
FIG. 2 Qualitative Classification Scheme for Oriented or Banded Microstructures
L = summarized length of feature interceptions by a single test line, perpendicular to the deformation direction (mm)
'
L = summarized length of feature interceptions by a single test line, perpendicular to the deformation direction (mm).
'
M = magnification.
L = true test line length in mm, that is, the test line length divided by M.
t
N
N = '
L'
L
t
N
N = ||
L||
L
t
P
P =
'
L'
>2N
L'
L
t
P
P =
||
L||
>2N
L ||
L
t
L = linear fraction of a feature on a single test line parallel to the deformation direction
L||
L = linear fraction of a feature on a single test line perpendicular to the deformation direction
L'
L
L = ||
L||
L
t
L
L = '
L'
L
t
n = number of measurement fields or number of microindentation impressions.
m = number of the test lines parallel to the deformation direction
k = number of the test lines perpendicular to the deformation direction
N
N¯ = (
L'
L'
n
E1268 − 19
N
N¯ =
( L ||
L||
n
P
P¯ = (
L'
L'
¯
>2N
L'
n
P
P¯ = (
L'
L'
¯
>2N
L'
n
P
P¯ = (
L ||
L||
¯
>2N
L ||
n
P
P¯ =
( L ||
L||
¯
>2N
L ||
n
¯
L
= (
L L||
L||
m
¯
L
= (
L L'
L'
k
AI = anisotropy index.
N
AI =
L'
N
L||
¯ ΣAI
=
AI
n
SB = mean center-to-center spacing of the bands.
'
SB =
'
.
¯
N
L'
V = volume fraction of the banded phase (constituent).
V
λ = mean edge-to-edge spacing of the bands, mean free path (distance).
'
12V
λ = V
'
¯
N
L'
Ω = degree of orientation of partially oriented linear structure elements on the two-dimensional plane-of-polish.
¯ ¯
Ω =
N 2N
L ' L ||
¯ ¯
N 10.571 N
L' L ||
¯ ¯
Ω =
P 2P
L' L ||
¯ ¯
P 10.571 P
L' L||
σ = standard deviation of linear fraction of a feature for all test lines that are parallel to the deformation direction on a
L
L||
single field of view
m
σ =
L 2
L||
¯
L 2 L
~ !
(
L|| L||
i
i51
!
m21
E1268 − 19
σ = standard deviation of linear fraction of a feature for all test lines that are perpendicular to the deformation direction
L
L'
on a single field of view
k
σ =
L 2
L'
¯
L 2 L
~ !
( L' L'
i
i51
!
k21
BR = banding rate in a single field of view
σ
BR = L
Li
σ
L
L'
¯ ΣBR
=
BR
n
¯ ¯
X¯ =
mean values (N¯ , N¯ , P¯ , P¯ , AI,BR)
L' L|| L' L||
s = estimate of standard deviation (σ).
t = a multiplier related to the number of fields examined and used in conjunction with the standard deviation of the
measurements to determine the 95 % CI.
95 % CI = 95 % confidence interval.
ts
95 % CI =
=
n
% RA = % relative accuracy.
95 % CI
% RA =
¯
X
4. Summary of Practice
4.1 The degree of microstructural banding or orientation is described quantitatively using metallographic specimens aligned
parallel to the deformation direction of the product.
4.2 Stereological methods are used to measure the number of bands per unit length, the inter-band or interparticle spacing and
the degree of anisotropy or orientation.
4.3 Microindentation hardness testing is used to determine the hardness of each type band present in hardened specimens and
the difference in hardness between the band types.
5. Significance and Use
5.1 This practice is used to assess the nature and extent of banding or orientation of microstructures of metals and other
materials where deformation and processing produce a banded or oriented condition.
5.2 Banded or oriented microstructures can arise in single phase, two phase or multiphase metals and materials. The appearance
of the orientation or banding is influenced by processing factors such as the solidification rate, the extent of segregation, the degree
of hot or cold working, the nature of the deformation process used, the heat treatments, and so forth.
5.3 Microstructural banding or orientation influence the uniformity of mechanical properties determined in various test
directions with respect to the deformation direction.
5.4 The stereological methods can be applied to measure the nature and extent of microstructural banding or orientation for any
metal or material. The microindentation hardness test procedure should only be used to determine the difference in hardness in
banded heat-treated metals, chiefly steels.
5.5 Isolated segregation may also be present in an otherwise reasonably homogeneous microstructure. Stereological methods
are not suitable for measuring individual features, instead use standard measurement procedures to define the feature size. The
microindentation hardness method may be used for such structures.
E1268 − 19
5.6 Results from these test methods may be used to qualify material for shipment in accordance with guidelines agreed upon
between purchaser and manufacturer, for comparison of different manufacturing processes or process variations, or to provide data
for structure-property-behavior studies.
6. Apparatus
6.1 A metallurgical (reflected-light) microscope is used to examine the microstructure of test specimens. Banding or orientation
is best observed using low magnifications, for example, 50× to 200×.
6.2 Stereological measurements are made by superimposing a test grid (consisting of a number of closely spaced parallel lines
of known length) on the projected image of the microstructure or on a photomicrograph. Measurements are made with the test lines
parallel and perpendicular to the deformation direction. The total length of the grid lines should be at least 500 mm.
6.3 These stereological measurements may be made using a semiautomatic tracing type image analyzer. The test grid is placed
over the image projected onto the digitizing tablet and a cursor is used for counting.
6.4 For certain microstructures where the contrast between the banded or oriented constituents is adequate, an automatic image
analyzer may be used for counting, where the TV scan lines for a live image, or image convolutionspixel lines of the bitmap
images, generated by high, electronically-generated test grids resolution digital cameras,, or other methods, for a digitized image,
are used rather than the grid lines of the plastic overlay or reticle.
6.5 A microindentation hardness tester is used to determine the hardness of each type of band in heat-treated steels or other
metals. The Knoop indenter is particularly well suited for this work.
7. Sampling and Test Specimens
7.1 In general, specimens should be taken from the final product form after all processing steps have been performed,
particularly those that would influence the nature and extent of banding. Because the degree of banding or orientation may vary
through the product cross section, the test plane should sample the entire cross section. If the section size is too large to permit
full cross sectioning, samples should be taken at standard locations, for example, subsurface, mid-radius (or quarter-point), and
center, or at specific locations based upon producer-purchaser agreements.
7.2 The degree of banding or orientation present is determined using longitudinal test specimens, that is, specimens where the
plane of polish is parallel to the deformation direction. For plate or sheet products, a planar oriented (that is, polished surface
parallel to the surface of the plate or sheet) test specimen, at subsurface, mid-thickness, or center locations, may also be prepared
and tested depending on the nature of the product application.
7.3 Banding or orientation may also be assessed on intermediate product forms, such as billets or bars, for material qualification
or quality control purposes. These test results, however, may not correlate directly with test results on final product forms. Test
specimens should be prepared as described in 7.1 and 7.2 but with the added requirement of choosing test locations with respect
to ingot or continuously cast slab/strand locations. The number and location of such test specimens should be defined by
producer-purchaser agreement.
7.4 Individual metallographic test specimens should have a polished surface area covering the entire cross section if possible.
The length of full cross-section samples, in the deformation direction, should be at least 10 mm (0.4 in.). If the product form is
too large to permit preparation of full cross sections, the samples prepared at the desired locations should have a minimum polished
2 2
surface area of 100 mm (0.16 in. ) with the sample length in the longitudinal direction at least 10 mm (0.4 in.).
8. Specimen Preparation
8.1 Metallographic specimen preparation should be performed in accordance with the guidelines and recommended practices
given in Methods E3. The preparation procedure must reveal the microstructure without excessive influence from preparation-
induced deformation or smearing.
8.2 Mounting of specimens may be performed depending on the nature of the test sample or if needed to accommodate
automatic polishing devices.
8.3 The microstructure should be revealed in strong contrast by any appropriate chemical or electrolytic etching method, by
tinting or staining, etc. Test Methods E407 list appropriate etchants for most metals and alloys. For certain materials, etching may
not be necessary as the naturally occurring reflectivity differences between the constituents may produce adequate contrast.
9. Calibration
9.1 Use a stage micrometer to determine the magnification of the projected image or at the photographic plane.
9.2 Use a ruler to determine the length of the test lines on the grid overlay in mm.
E1268 − 19
TABLE 1 Rules for N and P Counts
NOTE 1—Fig. 1 illustrates some of these counting rules.
1. N Interceptions—Count the number of individual particles, grains, or
patches of the constituent of interest crossed by the grid lines.
2. P Intersections—Count the number of unlike phase boundaries or
A
constituent boundaries crossed by the grid lines.
3. If two or more contiguous particles, grains, or patches of the phase
or constituent of interest are crossed by the grid lines (none of the
other phase or constituent between the particles where crossed)
count them as one particle intercepted (N = 1). For P intersections,
do not count phase or constituent boundaries between like particles,
grains, etc. This problem occurs most commonly in N and P
L|| L||
measurements in highly banded structures.
4. When a test line is tangent to the particle, grain, or patch of interest,
N is counted as ⁄2 and P as 1.
5. If a test line ends within a particle, count N as ⁄2 and P as 1.
6. If the entire test line lies completely within the phase or feature of
interest (this can occur for parallel counts of a highly banded
material), count N as ⁄2 and P as 0.
A
If possible, etch the specimens so that like phase or constituent boundaries are
not revealed, only unlike boundaries.
10. Procedure
10.1 Place the polished and etched specimen on the microscope stage, select a suitable low magnification, for example, 50× or
100×, and examine the microstructure. Align the specimen so that the deformation direction is horizontal on the projection screen.
Randomly select the initial field by arbitrarily moving the stage and accepting the new field without further stage adjustment.
10.1.1 Bright field illumination will be used for most measurements. However, depending on the alloy or material being
examined, other illumination modes, such as polarized light or differential interference contrast illumination, may be used.
10.1.2 Measurements may also be made by placing the test grid on photomicrographs (see Guide E883), taken of randomly
selected fields, at suitable magnifications.
10.2 Qualitatively define the nature and extent of the banding or orientation present in accordance with the following guidelines.
Examination at higher magnification may be required to identify and classify the constituents present. Fig. 2 describes the
classification approach.
10.2.1 Determine if the banding or orientation present represents variations in the etch intensity of a single phase or constituent,
such as might result from segregation in a tempered martensite alloy steel specimen, or is due to preferential alignment of one or
more phases or constituents in a two-phase or multi-phase specimen.
10.2.2 For orientation or banding in a two-phase or multi-phase specimen, determine if only the minor phase or constituent is
preferentially aligned within the matrix phase. Alternatively, both phases may be aligned with neither appearing as a matrix phase.
10.2.3 For two-phase (constituent) or multiphase (constituent) microstructures, determine if the aligned second phase
(constituent) is banded in a layered manner or exists in an oriented, non-banded, randomly distributed manner.
10.2.4 For cases where a second phase or constituent is banded or oriented within a non-banded, nonoriented matrix, determine
if the banded or oriented constituent exists as discrete particles (the particles may be globular or elongated) or as a continuously
aligned constituent.
10.2.5 Describe the appearance of the distribution of the second phase (or, either lighter or darker etching regions within a single
phase microstructure) in terms of the pattern present, for example: isotropic (nonoriented(non-oriented or non-banded), nearly
isotropic, partially banded, partially oriented, diffusely banded, narrow bands, broad bands, mixed narrow and broad bands, fully
oriented, etc.
10.3 Place the grid lines over the projected image or photomicrograph of the randomly selected field so that the grid lines are
perpendicular to the deformation direction. The grid should be placed without operator bias. Decide which phase or constituent
is banded. If both phases or constituents are banded, with no obvious matrix phase, choose one of the phases (constituents) for
counting. Generally, it is best to count the banded phase present in least amount. Either N or P , or both (see 10.3.1 – 10.3.4 for
L L
definitions), may be measured, using grid orientations perpendicular (') and parallel (||) to the deformation direction, depending
on the purpose of the measurements or as required by other specifications.
10.3.1 Measurement of N —with the test grid perpendicular to the deformation direction, count the number of discrete
LL'
particles or features intercepted by the test lines. For a two-phase structure, count all of the interceptions of the phase of interest,
that is, those that are clearly part of the bands and those that are not. When two or more contiguous particles, grains, or patches
of the phase or constituent of interest are crossed by the grid line, that is, none of the other phase or constituent is present between
the like particles, grains, or patches, count them as one interception (N = 1). Tangent hits are counted as one half an interception.
If a line ends within a particle, patch or grain, count it as one half an interception. Table 1 provides rules for counting while Fig.
E1268 − 19
1 illustrates the counting procedure. Calculate the number of feature interceptions per unit length perpendicular to the deformation
axis,
N , in accordance with:
L'
N
'
N 5 (1)
L'
L
t
where:
N = number of interceptions and
'
L = true test line length in mm, that is, the length of the grid lines in mm divided by the magnification, M.
t
10.3.2 Measurement of N —Rotate the test grid over the same field and location measured for N so that the test lines are
L|| L
oriented parallel to the deformation direction. Do not deliberately orient the grid lines over any particular microstructural feature
or features. Count all of the feature interceptions, N , with the test lines (in the same way as described in 10.3.1) whether they are
||
obviously part of the banded region or not. Calculate the number of interceptions per unit length parallel to the deformation axis,
N , in accordance with:
L||
N
??
N 5 (2)
L ??
L
t
where:
L = true test line length as defined in 10.3.1.
t
10.3.3 Measurement of P —With the test grid perpendicular to the deformation direction, count the number of times the test
L'
lines intersect a particle, phase or constituent boundary,
P , whether the particle, pha
...