ASTM E1268-99
(Practice)Standard Practice for Assessing the Degree of Banding or Orientation of Microstructures
Standard Practice for Assessing the Degree of Banding or Orientation of Microstructures
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.
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Designation: E 1268 – 99
AMERICAN SOCIETY FOR TESTING AND MATERIALS
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Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Practice for
Assessing the Degree of Banding or Orientation of
Microstructures
This standard is issued under the fixed designation E 1268; 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
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 1.6 The measured values are stated in SI units, which are
regarded as standard. Equivalent inch-pound values, when
1.1 This practice describes a procedure to qualitatively
listed, are in parentheses and may be approximate.
describe the nature of banded or oriented microstructures based
1.7 This standard does not purport to address all of the
on the morphological appearance of the microstructure.
safety problems, if any, associated with its use. It is the
1.2 This practice describes stereological procedures for
responsibility of the user of this standard to establish appro-
quantitative measurement of the degree of microstructural
priate safety and health practices and determine the applica-
banding or orientation.
bility of regulatory limitations prior to use.
NOTE 1—Although stereological measurement methods are used to
assess the degree of banding or alignment, the measurements are only
2. Referenced Documents
made on planes parallel to the deformation direction (that is, a longitudinal
2.1 ASTM Standards:
plane) and the three-dimensional characteristics of the banding or align-
A 370 Test Methods and Definitions for Mechanical Testing
ment are not evaluated.
of Steel Products
1.3 This practice describes a microindentation hardness test
A 572/A 572M Specification for High-Strength Low-Alloy
procedure for assessing the magnitude of the hardness differ-
Columbium-Vanadium Structural Steel
ences present in banded heat-treated steels. For fully marten-
A 588/A 588M Specification for High-Strength Low-Alloy
sitic carbon and alloy steels (0.10–0.65 %C), in the as-
Structural Steel with 50 ksi [345 MPa] Minimum Yield
quenched condition, the carbon content of the matrix and
Point to 4 in. [100 mm] Thick
segregate may be estimated from the microindentation hard-
E 3 Methods of Preparation of Metallographic Specimens
ness values.
E 7 Terminology Relating to Metallography
1.4 This standard does not cover chemical analytical meth-
E 140 Hardness Conversion Tables for Metals
ods for evaluating banded structures.
E 384 Test Method for Microhardness of Materials
1.5 This practice deals only with the recommended test
E 407 Test Methods for Microetching Metals and Alloys
methods and nothing in it should be construed as defining or
E 562 Practice for Determining Volume Fraction by Sys-
establishing limits of acceptability.
tematic Manual Point Count
E 883 Guide for Reflected-Light Photomicrography
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. Annual Book of ASTM Standards, Vol 01.03.
Current edition approved April 10, 1999. Published July 1999. Originally Annual Book of ASTM Standards, Vol 01.04.
published as E 1268 – 88. Last previous edition E 1268 – 94. Annual Book of ASTM Standards, Vol 03.01.
E 1268
3. Terminology that are crossed by the lines of a test grid (see Fig. 1). For
isolated particles in a matrix, the number of feature intersec-
3.1 Definitions—For definitions of terms used in this prac-
tions will equal twice the number of feature interceptions.
tice, see Terminology E 7.
3.2.4 oriented constituents—one or more second-phases
3.2 Definitions of Terms Specific to This Standard:
3.2.1 banded microstructure—separation, of one or more (constituents) elongated in a non-banded (that is, random
phases or constituents in a two-phase or multiphase microstruc- distribution) manner parallel to the deformation axis; the
ture, or of segregated regions in a single phase or constituent
degree of elongation varies with the size and deformability of
microstructure, into distinct layers parallel to the deformation the phase or constituent and the degree of hot- or cold-work
axis due to elongation of microsegregation; other factors may
reduction.
also influence band formation, for example, the hot working
3.2.5 stereological methods—procedures used to character-
finishing temperature, the degree of hot- or cold-work reduc-
ize three-dimensional microstructural features based on mea-
tion, or split transformations due to limited hardenability or
surements made on two-dimensional sectioning planes.
insufficient quench rate.
NOTE 2—Microstructural examples are presented in Annex A1 to
3.2.2 feature interceptions—the number of particles (or
illustrate the use of terminology for providing a qualitative description of
clusters of particles) of a phase or constituent of interest that
the nature and extent of the banding or orientation. Fig. 2 describes the
are crossed by the lines of a test grid. (see Fig. 1).
classification approach.
3.2.3 feature intersections—the number of boundaries be-
3.3 Symbols:
tween the matrix phase and the phase or constituent of interest
(A) (B)
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
E 1268
FIG. 2 Qualitative Classification Scheme for Oriented or Banded Microstructures
95 % CI 5 95 % confidence interval.
ts
N 5 number of feature interceptions with test lines 95 % CI 5
’
perpendicular to the deformation direction.
n
=
N 5 number of feature interceptions with test lines
||
% RA 5 % relative accuracy.
parallel to the deformation direction.
95 % CI
M 5 magnification. % RA 5
3 100
L 5 true test line length in mm, that is, the test line ¯
t X
length divided by M.
N
N 5
’ SB 5 mean center-to-center spacing of the bands.
L’ ’
L
SB 5
t ’
.
¯
N
L’
N
N 5
||
L||
L
t
V 5 volume fraction of the banded phase (constitu-
V
ent).
P 5 number of feature boundary intersections with
’
test lines perpendicular to the deformation di-
l 5 mean edge-to-edge spacing of the bands, mean
’
rection.
free path (distance).
P 5 number of feature boundary intersections with
|| 1 2 V
l 5
V
’
test lines parallel to the deformation direction.
¯
N
P L’
P 5 ’
L’
> 2N
L’
L
t
AI 5 anisotropy index.
¯ ¯
AI 5
N P
P L’ L’
P 5
||
L||
> 2N
L || ¯ ¯
L
N P
t L|| L||
n 5 number of measurement fields or number of V 5 degree of orientation of partially oriented linear
microindentation impressions.
structure elements on the two-dimensional
¯
(N
N 5
L’ plane-of-polish.
L ’
n ¯ ¯
V 5
N 2 N
L ’ L ||
¯ ¯
N 1 0.571 N
¯ (N L’ L ||
N 5
L ||
L||
n
¯ ¯
V 5
P 2 P
L’ L ||
¯
(P ¯ ¯
P 5
L’
P 1 0.571 P
L’
¯ L’ L||
> 2N
L’
n
¯
(P 4. Summary of Practice
P 5
L ||
L||
¯
> 2N
L ||
n
4.1 The degree of microstructural banding or orientation is
described qualitatively using metallographic specimens
¯ ¯ ¯
¯
X 5
mean values ( N , N ,¯P , P )
L’ L|| L ’ L||
aligned parallel to the deformation direction of the product.
s 5 estimate of standard deviation (s).
4.2 Stereological methods are used to measure the number
t 5 Student t multiplier for 95 % CI.
of bands per unit length, the inter-band or interparticle spacing
E 1268
and the degree of anisotropy or orientation. lines for a live image, or image convolutions , electronically-
generated test grids , or other methods, for a digitized image,
4.3 Microindentation hardness testing is used to determine
are used rather than the grid lines of the plastic overlay or
the hardness of each type band present in hardened specimens
reticle.
and the difference in hardness between the band types.
6.5 A microindentation hardness tester is used to determine
the hardness of each type of band in heat-treated steels or other
5. Significance and Use
metals. The Knoop indenter is particularly well suited for this
5.1 This practice is used to assess the nature and extent of
work.
banding or orientation of microstructures of metals and other
7. Sampling and Test Specimens
materials where deformation and processing produce a banded
or oriented condition.
7.1 In general, specimens should be taken from the final
5.2 Banded or oriented microstructures can arise in single product form after all processing steps have been performed,
phase, two phase or multiphase metals and materials. The particularly those that would influence the nature and extent of
banding. Because the degree of banding or orientation may
appearance of the orientation or banding is influenced by
vary through the product cross section, the test plane should
processing factors such as the solidification rate, the extent of
sample the entire cross section. If the section size is too large
segregation, the degree of hot or cold working, the nature of the
to permit full cross sectioning, samples should be taken at
deformation process used, the heat treatments, and so forth.
standard locations, for example, subsurface, mid-radius (or
5.3 Microstructural banding or orientation influence the
quarter-point), and center, or at specific locations based upon
uniformity of mechanical properties determined in various test
producer-purchaser agreements.
directions with respect to the deformation direction.
7.2 The degree of banding or orientation present is deter-
5.4 The stereological methods can be applied to measure the
mined using longitudinal test specimens, that is, specimens
nature and extent of microstructural banding or orientation for
where the plane of polish is parallel to the deformation
any metal or material. The microindentation hardness test
direction. For plate or sheet products, a planar oriented (that is,
procedure should only be used to determine the difference in
polished surface parallel to the surface of the plate or sheet) test
hardness in banded heat-treated metals, chiefly steels.
specimen, at subsurface, mid-thickness, or center locations,
5.5 Isolated segregation may also be present in an otherwise
may also be prepared and tested depending on the nature of the
reasonably homogeneous microstructure. Stereological meth-
product application.
ods are not suitable for measuring individual features, instead 7.3 Banding or orientation may also be assessed on inter-
use standard measurement procedures to define the feature
mediate product forms, such as billets or bars, for material
size. The microindentation hardness method may be used for qualification or quality control purposes. These test results,
such structures. however, may not correlate directly with test results on final
product forms. Test specimens should be prepared as described
5.6 Results from these test methods may be used to qualify
in 7.1 and 7.2 but with the added requirement of choosing test
material for shipment in accordance with guidelines agreed
locations with respect to ingot or continuously cast slab/strand
upon between purchaser and manufacturer, for comparison of
locations. The number and location of such test specimens
different manufacturing processes or process variations, or to
should be defined by producer-purchaser agreement.
provide data for structure-property-behavior studies.
7.4 Individual metallographic test specimens should have a
polished surface area covering the entire cross section if
6. Apparatus
possible. The length of full cross-section samples, in the
6.1 A metallurgical (reflected-light) microscope is used to
deformation direction, should be at least 10 mm (0.4 in.). If the
examine the microstructure of test specimens. Banding or
product form is too large to permit preparation of full cross
orientation is best observed using low magnifications, for
sections, the samples prepared at the desired locations should
2 2
example, 503 to 2003.
have a minimum polished surface area of 100 mm (0.16 in. )
with the sample length in the longitudinal direction at least 10
6.2 Stereological measurements are made by superimposing
mm (0.4 in.).
a test grid (consisting of a number of closely spaced parallel
lines of known length) on the projected image of the micro-
8. Specimen Preparation
structure or on a photomicrograph. Measurements are made
8.1 Metallographic specimen preparation should be per-
with the test lines parallel and perpendicular to the deformation
formed in accordance with the guidelines and recommended
direction. The total length of the grid lines should be at least
practices given in Methods E 3. The preparation procedure
500 mm.
6.3 These stereological measurements may be made using a
semiautomatic tracing type image analyzer. The test grid is
Lépine, M., “Image Convolutions and their Application to Quantitative
placed over the image projected onto the digitizing tablet and
Metallography,” Microstructural Science, Vol. 17, Image Analysis and Metal-
a cursor is used for counting.
lography, ASM International, Metals Park, OH, 1989, pp. 103–114.
Fowler, D.B., “A Method for Evaluating Plasma Spray Coating Porosity
6.4 For certain microstructures where the contrast between
Content Using Stereological Data Collected by Automatic Image Analysis,”
t
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