ASTM E1268-01(2007)

Standard Practice for Assessing the Degree of Banding or Orientation of Microstructures

SIGNIFICANCE AND USE
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.
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.
Microstructural banding or orientation influence the uniformity of mechanical properties determined in various test directions with respect to the deformation direction.
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.
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.
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.
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 standard 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 problems, 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.

General Information

• Status: Historical
• Publication Date: 30-Apr-2007
• ICS: 07.030 - Physics. Chemistry
• 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: E1268 − 01(Reapproved 2007)
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.Anumber 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
microindentationhardnessprocedurefordeterminingthedifferenceinhardnessbetweenbandsinheat
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 1.5 This practice deals only with the recommended test
methods and nothing in it should be construed as defining or
1.1 This practice describes a procedure to qualitatively
establishing limits of acceptability.
describethenatureofbandedororientedmicrostructuresbased
on the morphological appearance of the microstructure. 1.6 The measured values are stated in SI units, which are
regarded as standard. Equivalent inch-pound values, when
1.2 This practice describes stereological procedures for
listed, are in parentheses and may be approximate.
quantitative measurement of the degree of microstructural
1.7 This standard does not purport to address all of the
banding or orientation.
safety problems, if any, associated with its use. It is the
NOTE 1—Although stereological measurement methods are used to
responsibility of the user of this standard to establish appro-
assess the degree of banding or alignment, the measurements are only
priate safety and health practices and determine the applica-
madeonplanesparalleltothedeformationdirection(thatis,alongitudinal
plane) and the three-dimensional characteristics of the banding or align- bility of regulatory limitations prior to use.
ment are not evaluated.
2. Referenced Documents
1.3 This practice describes a microindentation hardness test
procedure for assessing the magnitude of the hardness differ-
2.1 ASTM Standards:
ences present in banded heat-treated steels. For fully marten-
A370Test Methods and Definitions for Mechanical Testing
sitic carbon and alloy steels (0.10–0.65%C), in the as-
of Steel Products
quenched condition, the carbon content of the matrix and
A572/A572MSpecification for High-Strength Low-Alloy
segregate may be estimated from the microindentation hard-
Columbium-Vanadium Structural Steel
ness values.
A588/A588MSpecification for High-Strength Low-Alloy
Structural Steel, up to 50 ksi [345 MPa] Minimum Yield
1.4 This standard does not cover chemical analytical meth-
Point, with Atmospheric Corrosion Resistance
ods for evaluating banded structures.
E3Guide for Preparation of Metallographic Specimens
E7Terminology Relating to Metallography
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 May 1, 2007. Published May 2007 . Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1988. Last previous edition approved in 2001 as E1268–01. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/E1268-01R07. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1268 − 01 (2007)
NOTE 1—The test grid lines have been shown oriented perpendicular (A) to the deformation axis and parallel (B) to the deformation axis. The counts
for N , N , P , and P are shown for counts made from top to bottom (A) or from left to right (B).
' || ' ||
NOTE 2—T indicates a tangent hit and E indicates that the grid line ended within the particle; both situations are handled as shown.
FIG. 1 Illustration of the Counting of Particle Interceptions (N) and Boundary Intersections (P) for an Oriented Microstructure
E140Hardness Conversion Tables for Metals Relationship isolated particles in a matrix, the number of feature intersec-
Among Brinell Hardness, Vickers Hardness, Rockwell tions will equal twice the number of feature interceptions.
Hardness, Superficial Hardness, Knoop Hardness, Sclero-
3.2.4 oriented constituents—one or more second-phases
scope Hardness, and Leeb Hardness
(constituents) elongated in a non-banded (that is, random
E384Test Method for Knoop and Vickers Hardness of
distribution) manner parallel to the deformation axis; the
Materials
degree of elongation varies with the size and deformability of
E407Practice for Microetching Metals and Alloys
the phase or constituent and the degree of hot- or cold-work
E562Test Method for Determining Volume Fraction by
reduction.
Systematic Manual Point Count
3.2.5 stereological methods—procedures used to character-
E883Guide for Reflected–Light Photomicrography
ize three-dimensional microstructural features based on mea-
3. Terminology surements made on two-dimensional sectioning planes.
3.1 Definitions—For definitions of terms used in this
NOTE 2—Microstructural examples are presented in Annex A1 to
practice, see Terminology E7.
illustrate the use of terminology for providing a qualitative description of
the nature and extent of the banding or orientation. Fig. 2 describes the
3.2 Definitions of Terms Specific to This Standard:
classification approach.
3.2.1 banded microstructure—separation, of one or more
3.3 Symbols:
phases or constituents in a two-phase or multiphase
microstructure, or of segregated regions in a single phase or
N = number of feature interceptions with test lines
'
constituent microstructure, into distinct layers parallel to the
perpendicular to the deformation direction.
deformation axis due to elongation of microsegregation; other
N = number of feature interceptions with test lines
||
factorsmayalsoinfluencebandformation,forexample,thehot
parallel to the deformation direction.
working finishing temperature, the degree of hot- or cold-work
M = magnification.
reduction, or split transformations due to limited hardenability
L = true test line length in mm, that is, the test line
t
or insufficient quench rate.
length divided by M.
N
3.2.2 feature interceptions—the number of particles (or N = '
L'
L
clusters of particles) of a phase or constituent of interest that
t
are crossed by the lines of a test grid. (see Fig. 1).
N
N = ||
L||
3.2.3 feature intersections—the number of boundaries be-
L
t
tween the matrix phase and the phase or constituent of interest
that are crossed by the lines of a test grid (see Fig. 1). For
E1268 − 01 (2007)
FIG. 2 Qualitative Classification Scheme for Oriented or Banded Microstructures
P = number of feature boundary intersections with
'
SB = mean center-to-center spacing of the bands.
test lines perpendicular to the deformation direc-
'
SB =
tion. '
.
¯
N
P = number of feature boundary intersections with
|| L'
test lines parallel to the deformation direction.
P
P = ' V = volume fraction of the banded phase (constitu-
L' V
>2N
L'
L ent).
t
P
λ = mean edge-to-edge spacing of the bands, mean
P = ||
'
L||
>2N
L ||
L free path (distance).
t
12V
λ =
V
'
¯
n = number of measurement fields or number of N
L'
microindentation impressions.
¯
N
N = AI = anisotropy index.
( L'
L'
¯ ¯
AI =
n N P
L' L'
¯ ¯
N P
L|| L||
¯
N
N = (
L ||
L||
n
Ω = degree of orientation of partially oriented linear
structureelementsonthetwo-dimensionalplane-
¯
P
P = (
L'
L'
¯
of-polish.
>2N
L'
n
¯ ¯
Ω =
N 2N
L ' L ||
¯ ¯
¯ P N 10.571 N
P = ( L' L ||
L ||
L||
¯
>2N
L ||
n
¯ ¯
Ω =
P 2P
L' L ||
¯ ¯ ¯ ¯ ¯
X = mean values (N , N , P , P )
¯ ¯
L' L|| L' L||
P 10.571 P
L' L||
s = estimate of standard deviation (σ).
t = a multiplier related to the number of fields
examined and used in conjunction with the stan-
4. Summary of Practice
dard deviation of the measurements to determine
the 95 % CI.
4.1 The degree of microstructural banding or orientation is
95% CI = 95% confidence interval.
described qualitatively using metallographic specimens
ts
95% CI =
aligned parallel to the deformation direction of the product.
=n
4.2 Stereological methods are used to measure the number
of bands per unit length, the inter-band or interparticle spacing
% RA = % relative accuracy.
95% CI and the degree of anisotropy or orientation.
% RA =
¯
X
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.
E1268 − 01 (2007)
5. Significance and Use generated test grids , or other methods, for a digitized image,
are used rather than the grid lines of the plastic overlay or
5.1 This practice is used to assess the nature and extent of
reticle.
banding or orientation of microstructures of metals and other
materials where deformation and processing produce a banded 6.5 Amicroindentation hardness tester is used to determine
or oriented condition. thehardnessofeachtypeofbandinheat-treatedsteelsorother
metals. The Knoop indenter is particularly well suited for this
5.2 Banded or oriented microstructures can arise in single
work.
phase, two phase or multiphase metals and materials. The
appearance of the orientation or banding is influenced by
7. Sampling and Test Specimens
processing factors such as the solidification rate, the extent of
7.1 In general, specimens should be taken from the final
segregation,thedegreeofhotorcoldworking,thenatureofthe
product form after all processing steps have been performed,
deformation process used, the heat treatments, and so forth.
particularly those that would influence the nature and extent of
5.3 Microstructural banding or orientation influence the
banding. Because the degree of banding or orientation may
uniformity of mechanical properties determined in various test
vary through the product cross section, the test plane should
directions with respect to the deformation direction.
sample the entire cross section. If the section size is too large
5.4 Thestereologicalmethodscanbeappliedtomeasurethe
to permit full cross sectioning, samples should be taken at
nature and extent of microstructural banding or orientation for
standard locations, for example, subsurface, mid-radius (or
any metal or material. The microindentation hardness test
quarter-point), and center, or at specific locations based upon
procedure should only be used to determine the difference in
producer-purchaser agreements.
hardness in banded heat-treated metals, chiefly steels.
7.2 The degree of banding or orientation present is deter-
5.5 Isolatedsegregationmayalsobepresentinanotherwise
mined using longitudinal test specimens, that is, specimens
reasonably homogeneous microstructure. Stereological meth-
where the plane of polish is parallel to the deformation
ods are not suitable for measuring individual features, instead
direction.Forplateorsheetproducts,aplanaroriented(thatis,
use standard measurement procedures to define the feature
polishedsurfaceparalleltothesurfaceoftheplateorsheet)test
size. The microindentation hardness method may be used for
specimen, at subsurface, mid-thickness, or center locations,
such structures.
mayalsobepreparedandtesteddependingonthenatureofthe
product application.
5.6 Results from these test methods may be used to qualify
material for shipment in accordance with guidelines agreed
7.3 Banding or orientation may also be assessed on inter-
upon between purchaser and manufacturer, for comparison of
mediate product forms, such as billets or bars, for material
different manufacturing processes or process variations, or to
qualification or quality control purposes. These test results,
provide data for structure-property-behavior studies.
however, may not correlate directly with test results on final
productforms.Testspecimensshouldbepreparedasdescribed
6. Apparatus
in 7.1 and 7.2 but with the added requirement of choosing test
locations with respect to ingot or continuously cast slab/strand
6.1 A metallurgical (reflected-light) microscope is used to
locations. The number and location of such test specimens
examine the microstructure of test specimens. Banding or
should be defined by producer-purchaser agreement.
orientation is best observed using low magnifications, for
example, 50× to 200×.
7.4 Individual metallographic test specimens should have a
polished surface area covering the entire cross section if
6.2 Stereologicalmeasurementsaremadebysuperimposing
possible. The length of full cross-section samples, in the
a test grid (consisting of a number of closely spaced parallel
deformationdirection,shouldbeatleast10mm(0.4in.).Ifthe
lines of known length) on the projected image of the micro-
product form is too large to permit preparation of full cross
structure or on a photomicrograph. Measurements are made
sections, the samples prepared at the desired locations should
withthetestlinesparallelandperpendiculartothedeformation
2 2
have a minimum polished surface area of 100 mm (0.16 in. )
direction. The total length of the grid lines should be at least
with the sample length in the longitudinal direction at least 10
500 mm.
mm (0.4 in.).
6.3 These stereological measurements may be made using a
semiautomatic tracing type image analyzer. The test grid is
8. Specimen Preparation
placed over the image projected onto the digitizing tablet and
8.1 Metallographic specimen preparation should be per-
a cursor is used for counting.
formed in accordance with the guidelines and recommended
6.4 For certain microstructures where the contrast between
practices given in Methods E3. The preparation procedure
the banded or oriented constituents is adequate, an automatic
must reveal the microstructure without excessive influence
image analyzer may be used for counting, where the TV scan
from preparation-in
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