ASTM E2567-11
(Test Method)Standard Test Method for Determining Nodularity And Nodule Count In Ductile Iron Using Image Analysis
Standard Test Method for Determining Nodularity And Nodule Count In Ductile Iron Using Image Analysis
SIGNIFICANCE AND USE
Qualitative measurement of “nodularity” and “nodule count” using visual estimations has been practiced for many years. These methods suffer from poor reproducibility and repeatability. The introduction of computer-aided image analysis enables metallographers to measure and count individual particles of interest in a microstructure with a high degree of precision. This greatly reduces measurement variations compared to visual estimation methods (see, for example, Test Method A247).
This method defines a procedure for measuring the number of nodules and the quality of nodularity of spherulitic graphite in a cast iron microstructure. The specimen’s location in a casting or cast test specimen, and the orientation of the plane-of-polish, are governed by product standards. When a product standard is not defined, choose the test location randomly or at specific systematically chosen depths as needed. The plane-of-polish may be parallel or perpendicular to the solidification direction, or chosen at random, depending upon the needs of the study.
This test method may be used to determine variations within a given test specimen, within a given location in a casting, between different locations in a casting, or for the same location in different castings over time. Results from this test method may be used to qualify material for shipment in accordance with guidelines agreed upon between purchaser and manufacturer or can be used to monitor process quality or product variations.
Measurements are performed using a computer-controlled automatic image analysis system.
A minimum number of specimens and a minimum surface area to be evaluated may be defined by producer-purchaser agreement, provided at least 500 particles meeting the minimum size requirements are measured. (See 5.6 for exceptions covering the minimum numbers of particles.)
The only exception to the 500-particle minimum assessment requirement is for large castings with a smallest cross-sectional dimension; f...
SCOPE
1.1 This test method is used to determine the percent nodularity and the nodule count per unit area (that is, number of nodules per mm2) using a light microscopical image of graphite in nodular cast iron. Images generated by other devices, such as a scanning electron microscope, are not specifically addressed, but can be utilized if the system is calibrated in both x and y directions.
1.2 Measurement of secondary or temper carbon in other types of cast iron, for example, malleable cast iron or in graphitic tool steels, is not specifically included in this standard because of the different graphite shapes and sizes inherent to such grades
1.3 This standard deals only with the recommended test method and nothing in it should be construed as defining or establishing limits of acceptability or fitness for purpose of the material tested.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:E2567–11
Standard Test Method for
Determining Nodularity And Nodule Count In Ductile Iron
Using Image Analysis
This standard is issued under the fixed designation E2567; 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 (ϵ) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
Ductile cast iron, also known as nodular cast iron, and spherulitic or spheroidal graphitic iron, is
produced with graphite in a spherulitic form. Nodularizing elements, such as magnesium, cerium,
lithium, sodium etc., are added to a molten metal bath of proper chemical composition to produce
discrete particles of spheroidal-shaped graphite. The control of graphite shape is critical to nodular
iron properties.Areproducible measurement method is required for evaluation of the cast product and
to control process variability. Shape is a difficult parameter to assess using standard chart methods,
unless the shape is very close to well-recognized geometric shapes. Nodule density is also difficult to
assess by chart methods as nodule size is also a variable and the chart cannot depict nodule density
variations for nodules of all possible sizes. Stereological and metrological methods provide unbiased
techniques for assessing structural variations. These procedures are best performed by image analysis
systems that eliminate operator subjectivity, bias and inaccuracies associated with manual application
of stereological and metrological methods. The metallographic sectioning plane will cut through the
nodules at random, producing images of graphite nodules with circular or near-circular peripheries
with a range of diameters.
1. Scope 1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This test method is used to determine the percent
responsibility of the user of this standard to establish appro-
nodularity and the nodule count per unit area (that is, number
priate safety and health practices and determine the applica-
of nodules per mm ) using a light microscopical image of
bility of regulatory limitations prior to use.
graphite in nodular cast iron. Images generated by other
devices, such as a scanning electron microscope, are not
2. Referenced Documents
specifically addressed, but can be utilized if the system is
2.1 ASTM Standards:
calibrated in both x and y directions.
A247 Test Method for Evaluating the Microstructure of
1.2 Measurement of secondary or temper carbon in other
Graphite in Iron Castings
types of cast iron, for example, malleable cast iron or in
E3 Guide for Preparation of Metallographic Specimens
graphitictoolsteels,isnotspecificallyincludedinthisstandard
E7 Terminology Relating to Metallography
because of the different graphite shapes and sizes inherent to
such grades
3. Terminology
1.3 This standard deals only with the recommended test
3.1 Definitions—For definitions of terms used in this test
method and nothing in it should be construed as defining or
method, see Terminology E7.
establishing limits of acceptability or fitness for purpose of the
3.2 Definitions of Terms Specific to This Standard:
material tested.
3.2.1 MFD—Maximum Feret Diameter
1.4 The values stated in SI units are to be regarded as
3.2.2 minimum size requirement—the size threshold below
standard. No other units of measurement are included in this
which graphite particles are eliminated from the analysis.
standard.
This test method is under the jurisdiction of ASTM Committee E04 on
Metallography and is the direct responsibility of Subcommittee E04.14 on Quanti- For referenced ASTM standards, visit the ASTM website, www.astm.org, or
tative Metallography. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved Jan. 1, 2011. Published February 2011. DOI; 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
E2567–11. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E2567–11
3.2.3 nodule—a discrete graphite particle that exceeds both 5.3 This test method may be used to determine variations
the required minimum size and shape factor as defined by this within a given test specimen, within a given location in a
method. casting,betweendifferentlocationsinacasting,orforthesame
3.2.4 nodule count—total number of graphite particles location in different castings over time. Results from this test
meeting the definition of a nodule in the area of interest (AOI). method may be used to qualify material for shipment in
3.2.5 nodule density (Nodule count/unit area)—number of accordance with guidelines agreed upon between purchaser
nodules per mm . and manufacturer or can be used to monitor process quality or
3.2.6 nodularity—degree of roundness, or closeness to a product variations.
circular periphery, of a graphite particle in ductile iron based 5.4 Measurements are performed using a computer-
upon the shape factor. controlled automatic image analysis system.
3.2.7 percent nodularity by area—the total area of particles 5.5 A minimum number of specimens and a minimum
defined as nodules which meet the minimum size requirements surface area to be evaluated may be defined by producer-
divided by the total area of all particles which meet the purchaser agreement, provided at least 500 particles meeting
minimum size requirements, expressed as a percentage. See the minimum size requirements are measured. (See 5.6 for
8.10. exceptions covering the minimum numbers of particles.)
3.2.8 percent nodularity by count—the total number of 5.6 The only exception to the 500-particle minimum assess-
particles defined as nodules which meet the minimum size ment requirement is for large castings with a smallest cross-
requirements divided by the total number of all particles which sectional dimension; for example being 15 cm. Graphite
meet the minimum size requirements, expressed as a percent- particles in such castings are very large typically above Test
age. See 8.10. MethodA247size4or160µm,andnodulecountsarelow.The
3.2.9 shape factor—a number between 0.00 and 1.0 result- error in measuring a large graphite particle is very low.
ing from formula (Eq 2) of this method. Therefore, when the mean graphite particle MFD is above Test
3.2.10 spherulitic graphite—in cast iron, a small, MethodA247size4or160µmthenumberofparticlesrequired
spheroidal-shaped crystalline carbon body with a radial growth for a measurement may be reduced to 100 particles. However,
structure. the particles measured must still meet the minimum size
requirement.
4. Summary of Test Method
6. Test Specimens and Statistical Sampling
4.1 This test method uses an image analyzer to measure the
6.1 Test Specimens:
degree of roundness of graphite particles, viewed on a metal-
6.1.1 The number and location of test specimens, and the
lographic sectioning plane, that are above a minimum size in
orientationoftheplane-of-polish,shouldbedefinedbyproduct
order to determine percent nodularity and nodule density. The
standards or by producer-purchaser agreements. When this is
magnification used for the analysis is based on a Maximum
not possible, the metallographer should use common-sense
Feret Diameter (MFD) ≥ 50 pixels and ≤ 125 pixels for the
engineering analysis to decide on the number of specimens
average size graphite particle being measured. Particles having
based upon the size of the casting, or the number of castings in
aMFD<10%oftheaverageMFDarenotmeasured.Threshold
the lot. The plane-of-polish may be chosen at random, or
settings are established by the operator, and can be influenced
parallelorperpendiculartothesolidificationdirection,depend-
by factors such as polishing technique, illumination intensity
ing upon the information required. The number and locations
and uniformity, and lamp voltage and stability.
oftestspecimens,andtheorientationofplane-of-polish,canbe
5. Significance and Use
defined by product standards or producer-purchaser agree-
5.1 Qualitative measurement of “nodularity” and “nodule ments.
count” using visual estimations has been practiced for many 6.1.2 Each specimen should have a surface area large
years. These methods suffer from poor reproducibility and enough to provide a number of fields-of-view at the required
repeatability. The introduction of computer-aided image analy- magnification. In general, a 10 3 10 mm surface area, or its
sis enables metallographers to measure and count individual equivalent area, is an acceptable approximate specimen size.
particles of interest in a microstructure with a high degree of 6.1.3 It is recommended to avoid sampling in the near-
precision. This greatly reduces measurement variations com- surface region, as this region will exhibit large variations in
pared to visual estimation methods (see, for example, Test graphite structure as compared to areas further below the
Method A247). casting surface.
5.2 This method defines a procedure for measuring the 6.2 Specimen Preparation:
number of nodules and the quality of nodularity of spherulitic 6.2.1 Metallographic specimen preparation must be care-
graphite in a cast iron microstructure. The specimen’s location fully controlled to produce an acceptable quality surface for
in a casting or cast test specimen, and the orientation of the image analysis. Guidelines for preparing metallographic speci-
plane-of-polish, are governed by product standards. When a mens are given in Guide E3.
product standard is not defined, choose the test location 6.2.2 Mounting of specimens is not required, but may
randomly or at specific systematically chosen depths as facilitate identification coding or grinding and polishing.
needed. The plane-of-polish may be parallel or perpendicular 6.2.3 The polishing procedure must remove all deformation
to the solid
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