ASTM E2567-16a(2023)

Standard Test Method for Determining Nodularity And Nodule Count In Ductile Iron Using Image Analysis

SIGNIFICANCE AND USE
5.1 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).  
5.2 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.  
5.3 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.  
5.4 Measurements are performed using a computer-controlled automatic image analysis system.  
5.5 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. The number of particles analyzed shall be indicated in the final analysis report (see 9.6).
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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.6 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.

General Information

• Status: Published
• Publication Date: 31-Mar-2023
• ICS: 77.080.10 - Irons
• Technical Committee: E04 - Metallography
• Drafting Committee: E04.14 - Quantitative Metallography

Relations

• Refers: ASTM A247-24 - Standard Test Method for Visual Evaluation of Graphite in Iron Castings
• Effective Date: 01-Apr-2024
• Refers: ASTM A247-19 - Standard Test Method for Evaluating the Microstructure of Graphite in Iron Castings
• Effective Date: 01-Mar-2019
• Refers: ASTM A247-17 - Standard Test Method for Evaluating the Microstructure of Graphite in Iron Castings
• Effective Date: 01-Jul-2017
• Refers: ASTM A247-16a - Standard Test Method for Evaluating the Microstructure of Graphite in Iron Castings
• Effective Date: 01-Apr-2016
• Refers: ASTM A247-16 - Standard Test Method for Evaluating the Microstructure of Graphite in Iron Castings
• Effective Date: 15-Mar-2016
• Refers: ASTM E7-15 - Standard Terminology Relating to Metallography
• Effective Date: 01-Jun-2015
• Refers: ASTM E7-14 - Standard Terminology Relating to Metallography
• Effective Date: 01-Nov-2014
• Refers: ASTM A247-10 - Standard Test Method for Evaluating the Microstructure of Graphite in Iron Castings
• Effective Date: 01-Mar-2010
• Refers: ASTM E7-03(2009) - Standard Terminology Relating to Metallography
• Effective Date: 01-Oct-2009
• Refers: ASTM E3-01(2007) - Standard Guide for Preparation of Metallographic Specimens
• Effective Date: 01-Jul-2007
• Refers: ASTM E3-01(2007)e1 - Standard Guide for Preparation of Metallographic Specimens
• Effective Date: 01-Jul-2007
• Refers: ASTM A247-06e1 - Standard Test Method for Evaluating the Microstructure of Graphite in Iron Castings
• Effective Date: 15-Nov-2006
• Refers: ASTM A247-06 - Standard Test Method for Evaluating the Microstructure of Graphite in Iron Castings
• Effective Date: 15-Nov-2006
• Refers: ASTM E7-03 - Standard Terminology Relating to Metallography
• Effective Date: 10-May-2003
• Refers: ASTM E7-00 - Standard Terminology Relating to Metallography
• Effective Date: 10-Dec-2001

Overview

ASTM E2567-16a(2023) - Standard Test Method for Determining Nodularity and Nodule Count in Ductile Iron Using Image Analysis - provides a quantitative procedure for assessing the quality and quantity of graphite nodules in ductile (nodular) cast iron. Replacing older subjective visual estimation methods, this standard leverages computer-controlled image analysis to accurately measure and count graphite particles. Such precise, repeatable, and highly reproducible measurement enhances material evaluation and process monitoring in metallurgical applications, supporting quality control and compliance with product specifications.

Key Topics

• Nodularity Measurement: Quantifies the degree of roundness (circularity) of graphite nodules in ductile iron, a crucial property influencing mechanical characteristics.
• Nodule Count: Reports the number of graphite nodules per unit area, supporting detailed microstructural analysis.
• Image Analysis Technology: Utilizes automatic, computer-aided image analysis systems to minimize operator bias and increase precision compared to manual methods.
• Specimen Preparation: Emphasizes careful metallographic preparation to ensure accurate segmentation and measurement of nodules. The recommended surface preparation techniques help reduce deformation, scratches, or artifacts that may impact results.
• Sampling and Calibration: Specifies the minimum number of particles (at least 500 meeting size criteria) to be examined per location, calibration procedures, and field-of-view considerations to ensure statistically significant results.
• Reporting Requirements: Details the information required in analysis reports, including nodularity percentage, nodule density, instrument calibration data, and any deviations from the standard.
• Scope Clarifications: Applies specifically to ductile iron microstructures under light microscopy, with optional use for other imaging devices if properly calibrated.

Applications

The ASTM E2567 standard is widely used in the metallurgical industry for:

• Quality Assurance of Ductile Iron: Ensures the microstructural consistency of nodular cast iron, a material known for its high strength and ductility.
• Supplier and Purchaser Agreements: Provides an objective basis for qualifying and accepting shipments based on precise graphite nodularity and density measurements.
• Process Monitoring: Assists foundries and quality control laboratories in monitoring casting processes, identifying variability, and adjusting procedures to maintain desired graphite structures.
• Research and Development: Supports material scientists and engineers studying the effects of alloying, process changes, or thermal treatments on graphite morphology in cast iron.
• Compliance and Certification: Satisfies requirements in product standards and regulatory specifications mandating quantitative evaluation of cast iron microstructure.

Related Standards

For comprehensive metallurgical analysis and graphite characterization, the following related standards are often referenced alongside ASTM E2567-16a(2023):

• ASTM A247 - Test Method for Evaluating the Microstructure of Graphite in Iron Castings
• ASTM E3 - Guide for Preparation of Metallographic Specimens
• ASTM E7 - Terminology Relating to Metallography

Practical Value

The implementation of ASTM E2567-16a(2023) in ductile iron production environments:

• Reduces measurement variability, ensuring consistent, reliable data
• Improves confidence in material certification and shipment qualification
• Aligns with international quality practices, supporting global trade compliance
• Enables precise documentation and traceable reporting for audits and quality management systems

For iron foundries, quality labs, and metal casting suppliers, adoption of this image analysis standard is essential for maintaining high standards of ductile iron product integrity and supporting ongoing process improvement.

Standards Content (Sample)

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.
Designation: E2567 − 16a (Reapproved 2023)
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 (´) 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. A reproducible 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 1.4 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
1.1 This test method is used to determine the percent
standard.
nodularity and the nodule count per unit area (that is, number
1.5 This standard does not purport to address all of the
of nodules per mm ) using a light microscopical image of
safety concerns, if any, associated with its use. It is the
graphite in nodular cast iron. Images generated by other
responsibility of the user of this standard to establish appro-
devices, such as a scanning electron microscope, are not
priate safety, health, and environmental practices and deter-
specifically addressed, but can be utilized if the system is
mine the applicability of regulatory limitations prior to use.
calibrated in both x and y directions.
1.6 This international standard was developed in accor-
1.2 Measurement of secondary or temper carbon in other
dance with internationally recognized principles on standard-
types of cast iron, for example, malleable cast iron or in
ization established in the Decision on Principles for the
graphitic tool steels, is not specifically included in this standard
Development of International Standards, Guides and Recom-
because of the different graphite shapes and sizes inherent to
mendations issued by the World Trade Organization Technical
such grades
Barriers to Trade (TBT) Committee.
1.3 This standard deals only with the recommended test
2. Referenced Documents
method and nothing in it should be construed as defining or
2.1 ASTM Standards:
establishing limits of acceptability or fitness for purpose of the
A247 Test Method for Evaluating the Microstructure of
material tested.
Graphite in Iron Castings
E3 Guide for Preparation of Metallographic Specimens
E7 Terminology Relating to Metallography
This test method is under the jurisdiction of ASTM Committee E04 on
Metallography and is the direct responsibility of Subcommittee E04.14 on Quanti-
tative Metallography. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved April 1, 2023. Published April 2023. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 2011. Last previous edition approved in 2016 as E2567–16a. DOI; Standards volume information, refer to the standard’s Document Summary page on
10.1520/E2567–16A(2023). the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2567 − 16a (2023)
3. Terminology 5.2 This method defines a procedure for measuring the
number of nodules and the quality of nodularity of spherulitic
3.1 Definitions—For definitions of terms used in this test
graphite in a cast iron microstructure. The specimen’s location
method, see Terminology E7.
in a casting or cast test specimen, and the orientation of the
3.2 Definitions of Terms Specific to This Standard:
plane-of-polish, are governed by product standards. When a
3.2.1 MFD—Maximum Feret Diameter
product standard is not defined, choose the test location
randomly or at specific systematically chosen depths as
3.2.2 minimum size requirement—the size threshold below
needed. The plane-of-polish may be parallel or perpendicular
which graphite particles are eliminated from the analysis.
to the solidification direction, or chosen at random, depending
3.2.3 nodule—a discrete graphite particle that exceeds both
upon the needs of the study.
the required minimum size and shape factor as defined by this
5.3 This test method may be used to determine variations
method.
within a given test specimen, within a given location in a
3.2.4 nodule count—total number of graphite particles
casting, between different locations in a casting, or for the same
meeting the definition of a nodule in the area of interest (AOI).
location in different castings over time. Results from this test
3.2.5 nodule density (Nodule count/unit area)—number of
method may be used to qualify material for shipment in
nodules per mm .
accordance with guidelines agreed upon between purchaser
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
upon the shape factor.
5.4 Measurements are performed using a computer-
controlled automatic image analysis system.
3.2.7 percent nodularity by area—the total area of particles
defined as nodules which meet the minimum size requirements
5.5 A minimum number of specimens and a minimum
divided by the total area of all particles which meet the
surface area to be evaluated may be defined by producer-
minimum size requirements, expressed as a percentage. See
purchaser agreement, provided at least 500 particles meeting
8.10.
the minimum size requirements are measured. The number of
particles analyzed shall be indicated in the final analysis report
3.2.8 shape factor—a number between 0.00 and 1.0 result-
(see 9.6).
ing from formula (Eq 2) of this method.
3.2.9 spherulitic graphite—in cast iron, a small, spheroidal-
6. Test Specimens and Statistical Sampling
shaped crystalline carbon body with a radial growth structure.
6.1 Test Specimens:
4. Summary of Test Method 6.1.1 The number and location of test specimens, and the
orientation of the plane-of-polish, should be defined by product
4.1 This test method uses an image analyzer to measure the
standards or by producer-purchaser agreements. When this is
degree of roundness of graphite particles, viewed on a metal-
not possible, the metallographer should use common-sense
lographic sectioning plane, that are above a minimum size in
engineering analysis to decide on the number of specimens
order to determine percent nodularity and nodule density. A
based upon the size of the casting, or the number of castings in
common objective used for the analysis is 10×, for an overall
the lot. The plane-of-polish may be chosen at random, or
magnification of approximately 100×. Higher magnification
parallel or perpendicular to the solidification direction, depend-
objectives (20× or more, for an overall approximate magnifi-
ing upon the information required. The number and locations
cation of 200×) can be used to characterize small nodules, and
of test specimens, and the orientation of plane-of-polish, can be
a 5× magnification objective (approximate overall magnifica-
defined by product standards or producer-purchaser agree-
tion of 50×) can be used to characterize very large nodules. The
ments.
magnification used shall be in accordance to purchaser-supplier
6.1.2 Each specimen should have a surface area large
agreement and, shall be reported in the final report (see9.18).
enough to provide a number of fields-of-view at the required
Threshold settings are established by the operator, and can be
magnification. In general, a 10 mm × 10 mm surface area, or its
influenced by factors such as polishing technique, illumination
equivalent area, is an acceptable approximate specimen size.
intensity and uniformity, and lamp voltage and stability.
6.1.3 It is recommended to avoid sampling in the near-
surface region, as this region will exhibit large variations in
5. Significance and Use
graphite structure as compared to areas further below the
5.1 Qualitative measurement of “nodularity” and “nodule
casting surface.
count” using visual estimations has been practiced for many
6.2 Specimen Preparation:
years. These methods suffer from poor reproducibility and
6.2.1 Metallographic specimen preparation must be care-
repeatability. The introduction of computer-aided image analy-
fully controlled to produce an acceptable quality surface for
sis enables metallographers to measure and count individual
image analysis. Guidelines for preparing metallographic speci-
particles of interest in a microstructure with a high degree of
mens are given in Guide E3.
precision. This greatly reduces measurement variations com-
pared to visual estimation methods (see, for example, Test 6.2.2 Mounting of specimens is not required, but may
Method A247). facilitate identification coding or grinding and polishing.
E2567 − 16a (2023)
6.2.3 The polishing procedure must remove all deformation 8.2.1 At low magnification, survey the mount for
and damage induced by the cutting and grinding procedure. homogeneity, polishing defects and abnormalities.
Scratches and smeared graphite or matrix must be removed by
8.2.2 The default objective magnification used f
...