Designation: A 247 – 67 (Reapproved 1998)
Standard Test Method for
Evaluating the Microstructure of Graphite in Iron Castings1
This standard is issued under the fixed designation A 247; 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.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope
1.1 This test method covers the classification of graphite in
cast irons in terms of type, distribution, and size. This test
method is intended to be applicable for all iron-carbon alloys
containing graphite particles, and may be applied to gray irons,
malleable irons, and the ductile (nodular) irons.
1.2 The reference standards included in this test method are
in no way to be construed as specifications. In an appropriate
specification for a specific material where graphite microstructure
is an important consideration this test method may be used
as a reference to define concisely the graphite microstructure
required.
1.3 These standards are offered primarily to permit accurate
reporting of microstructures of cast irons and to facilitate the
comparison of reports by different laboratories or investigators.
1.4 This standard does not purport to address all of the
safety problems associated with its use. It is the responsibility
of the user of this standard to consult and establish appropriate
safety and health practices and determine the applicability of
regulatory limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
E 3 Methods of Preparation of Metallographic Specimens2
3. Summary of Test Method
3.1 The reference diagrams included in this standard form
the basis for classification. Characteristic features of graphite
particles are designated by numerals and letters. Type, distribution,
and size of observed graphite are compared with the
idealized microstructures in the standard charts and rated
accordingly as closely as possible to the equal or similar
microstructures in the charts.
4. Significance and Use
4.1 The comparison of observed graphite particles with the
structures shown in the charts give only purely descriptive
information on the type, distribution, and size of the graphite in
the sample being evaluated. It does not indicate except in a
very broad way the origin of the graphite, or the suitability of
the iron-carbon alloy for a particular service.
5. Test Specimens or Samples
5.1 The preferred sample is a section cut from an actual
casting that is being evaluated. When this is impractical, a test
lug or projection often can be cast attached to the casting and
sawed or broken off to be used as the sample. If neither of these
methods is convenient, microscopical test coupons, such as that
recommended by the Ductile Iron Research Committee (12K)
of the American Foundrymen’s Society3 should be cast from
metal representative of the castings poured.
6. Polishing
6.1 Grinding and polishing may follow the usual accepted
metallographic procedures as covered in Methods E 3, except
that care must be taken that the graphite is retained at the
polished surface and not torn or dragged out. Use of diamond
powder polishing compound in one of the final stages of
polishing is very effective in retaining the graphite at the
polished surface.
7. Classification of Graphite Form with Chart
7.1 The graphite form type chart (Plate I)4 is used as a
reference standard by scanning the polished specimen under
the microscope and noting the graphite forms in the microstructure
that more nearly correspond to type designations on
the chart.
7.2 Type I is the normal and usually desirable graphite form
in ductile iron, although the presence of Type II graphite forms
has little or no adverse effect on properties. Graphite forms
represented by Types IV through VI often occur in ductile iron
in conjunction with Types I and II. The percentages of each
graphite type are estimated by observation, or better, by
counting the particles of each type. Types present in a sample
are to be reported in percentages to total 100. Any convenient
magnification that clearly reveals the graphite form may be
used.
7.3 Type III is the graphite form most often seen in
malleable iron castings after annealing. Some malleable irons
may contain Types I or II graphite particles also.
1 This test method is under the jurisdiction of ASTM Committee A-4 on Iron
Castings and is the direct responsibility of Subcommittee A04.21 on Testing.
Current edition effective Aug. 25, 1967. Originally issued 1941. Replaces
A 247 – 47.
2 Annual Book of ASTM Standards, Vol 03.01.
3 Transactions, American Foundrymen’s Society, 1960, p. 655.
4 Plates I, II, and III may be obtained from ASTM Headquarters. Order PCN
12-102470-09.
1
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from