ASTM E3-01(2007)
(Practice)Standard Guide for Preparation of Metallographic Specimens
Standard Guide for Preparation of Metallographic Specimens
SIGNIFICANCE AND USE
Microstructures have a strong influence on the properties and successful application of metals and alloys. Determination and control of microstructure requires the use of metallographic examination.
Many specifications contain a requirement regarding microstructure; hence, a major use for metallographic examination is inspection to ensure that the requirement is met. Other major uses for metallographic examination are in failure analysis, and in research and development.
Proper choice of specimen location and orientation will minimize the number of specimens required and simplify their interpretation. It is easy to take too few specimens for study, but it is seldom that too many are studied.
SCOPE
1.1 The primary objective of metallographic examinations is to reveal the constituents and structure of metals and their alloys by means of a light optical or scanning electron microscope. In special cases, the objective of the examination may require the development of less detail than in other cases but, under nearly all conditions, the proper selection and preparation of the specimen is of major importance. Because of the diversity in available equipment and the wide variety of problems encountered, the following text presents for the guidance of the metallographer only those practices which experience has shown are generally satisfactory; it cannot and does not describe the variations in technique required to solve individual specimen preparation problems.
Note 1 - For a more extensive description of various metallographic techniques, refer to Samuels, L. E., Metallographic Polishing by Mechanical Methods, American Society for Metals (ASM) Metals Park, OH, 3rd Ed., 1982; Petzow, G., Metallographic Etching, ASM, 1978; and VanderVoort, G., Metallography: Principles and Practice, McGraw Hill, NY, 2nd Ed., 1999.
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:E3–01 (Reapproved 2007)
Standard Guide for
Preparation of Metallographic Specimens
This standard is issued under the fixed designation E 3; 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.Asuperscript
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 E 1077 Test Methods for Estimating the Depth of Decar-
burization of Steel Specimens
1.1 The primary objective of metallographic examinations
E 1122 Practice for Obtaining JK Inclusion Ratings Using
is to reveal the constituents and structure of metals and their
Automatic Image Analysis
alloys by means of a light optical or scanning electron
E 1245 Practice for Determining the Inclusion or Second-
microscope. In special cases, the objective of the examination
Phase Constituent Content of Metals by Automatic Image
may require the development of less detail than in other cases
Analysis
but, under nearly all conditions, the proper selection and
E 1268 Practice for Assessing the Degree of Banding or
preparationofthespecimenisofmajorimportance.Becauseof
Orientation of Microstructures
the diversity in available equipment and the wide variety of
E 1558 Guide for Electrolytic Polishing of Metallographic
problems encountered, the following text presents for the
Specimens
guidance of the metallographer only those practices which
E 1920 Guide for Metallographic Preparation of Thermal
experience has shown are generally satisfactory; it cannot and
Sprayed Coatings
does not describe the variations in technique required to solve
individual specimen preparation problems.
3. Terminology
NOTE 1—For a more extensive description of various metallographic
3.1 Definitions:
techniques,refertoSamuels,L.E., Metallographic Polishing by Mechani-
3.1.1 For definitions used in this practice, refer to Termi-
cal Methods, American Society for Metals (ASM) Metals Park, OH, 3rd
nologyE7.
Ed., 1982; Petzow, G., Metallographic Etching, ASM, 1978; and Vander-
3.2 Definitions of Terms Specific to This Standard:
Voort, G., Metallography: Principles and Practice,McGrawHill,NY,2nd
3.2.1 castable mount—a metallographic mount generally
Ed., 1999.
made from a two component castable plastic. One component
1.2 This standard does not purport to address all of the
is the resin and the other hardener. Both components can he
safety concerns, if any, associated with its use. It is the
liquid or one liquid and a powder. Castable mounts generally
responsibility of the user of this standard to establish appro-
do not require heat and pressure to cure.
priate safety and health practices and determine the applica-
3.2.2 compression mount—a metallographic mount made
bility of regulatory limitations prior to use.
using plastic that requires both heat and pressure for curing.
3.2.3 planar grinding—is the first grinding step in a prepa-
2. Referenced Documents
ration procedure used to bring all specimens into the same
2.1 ASTM Standards:
plane of polish. It is unique to semi or fully automatic
A 90/A 90M Test Method for Weight [Mass] of Coating on
preparation equipment that utilize specimen holders.
Iron and Steel Articles with Zinc or Zinc-Alloy Coatings
3.2.4 rigid grinding disc—a non-fabric support surface,
E7 Terminology Relating to Metallography
such as a composite of metal/ceramic or metal/polymer
E45 Test Methods for Determining the Inclusion Content
charged with an abrasive (usually 6 to 15µm diamond par-
of Steel
ticles), and used as the fine grinding operation in a metallo-
E 340 Test Method for Macroetching Metals and Alloys
graphic preparation procedure.
E 407 Practice for Microetching Metals and Alloys
E 768 Guide for Preparing and Evaluating Specimens for
4. Significance and Use
Automatic Inclusion Assessment of Steel
4.1 Microstructures have a strong influence on the proper-
ties and successful application of metals and alloys. Determi-
nation and control of microstructure requires the use of
ThisguideisunderthejurisdictionofASTMCommitteeE04onMetallography
metallographic examination.
and is the direct responsibility of Subcommittee E04.01 on Specimen Preparation.
Current edition approved July 1, 2007. Published September 2007. Originally
approved in 1921. Last previous edition approved in 2001 asE3–01. Withdrawn.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E3–01 (2007)
4.2 Many specifications contain a requirement regarding 5.3.5 Depth of corrosion,
microstructure; hence, a major use for metallographic exami- 5.3.6 Thickness of protective coatings, and
nationisinspectiontoensurethattherequirementismet.Other 5.3.7 Structure of protective coating. See Guide E 1920.
major uses for metallographic examination are in failure 5.4 Longitudinal sections taken parallel to the main axis of
analysis, and in research and development. the material are often used for revealing the following infor-
4.3 Proper choice of specimen location and orientation will mation:
minimize the number of specimens required and simplify their 5.4.1 Inclusion content of steel (see PracticesE45, E 768,
interpretation. It is easy to take too few specimens for study, E 1122, and E 1245),
but it is seldom that too many are studied. 5.4.2 Degree of plastic deformation, as shown by grain
distortion,
5. Selection of Metallographic Specimens
5.4.3 Presence or absence of banding in the structure (see
5.1 The selection of test specimens for metallographic
Practice E 1268), and
examination is extremely important because, if their interpre-
5.4.4 The microstructure attained with any heat treatment.
tationistobeofvalue,thespecimensmustberepresentativeof
5.5 The locations of surfaces examined should always be
the material that is being studied. The intent or purpose of the
giveninreportingresultsandinanyillustrativemicrographs.A
metallographic examination will usually dictate the location of
suitablemethodofindicatingsurfacelocationsisshowninFig.
the specimens to be studied. With respect to purpose of study,
1.
metallographic examination may be divided into three classi-
6. Size of Metallographic Specimens
fications:
5.1.1 General Studies or Routine Work—Specimens should
6.1 For convenience, specimens to be polished for metallo-
be chosen from locations most likely to reveal the maximum
graphicexaminationaregenerallynotmorethanabout12to25
variations within the material under study. For example,
mm (0.5 to 1.0 in.) square, or approximately 12 to 25 mm in
specimens could be taken from a casting in the zones wherein
diameter if the material is cylindrical. The height of the
maximum segregation might be expected to occur as well as
specimen should be no greater than necessary for convenient
specimens from sections where segregation could be at a
handling during polishing.
minimum. In the examination of strip or wire, test specimens
6.1.1 Larger specimens are generally more difficult to pre-
could be taken from each end of the coils.
pare.
5.1.2 Study of Failures—Test specimens should be taken as
6.1.2 Specimens that are, fragile, oddly shaped or too small
closely as possible to the fracture or to the initiation of the
to be handled readily during polishing should be mounted to
failure. Before taking the metallographic specimens, study of
ensure a surface satisfactory for microscopical study. There
the fracture surface should be complete, or, at the very least,
the fracture surface should be documented. In many cases,
specimens should be taken from a sound area for a comparison
of structures and properties.
5.1.3 Research Studies—The nature of the study will dictate
specimen location, orientation, etc. Sampling will usually be
more extensive than in routine examinations.
5.2 Having established the location of the metallographic
samples to be studied, the type of section to be examined must
be decided.
5.2.1 For a casting, a section cut perpendicular to the
surfacewillshowthevariationsinstructurefromtheoutsideto
the interior of the casting.
5.2.2 In hot-worked or cold-worked metals, both transverse
and longitudinal sections should be studied. Special investiga-
tions may require specimens with surfaces prepared parallel to
the original surface of the product.
5.2.3 In the case of wire and small rounds, a longitudinal
Symbol in
Suggested Designation
section through the center of the specimen proves advanta-
Diagram
geous when studied in conjunction with the transverse section.
5.3 Transverse sections or cross sections taken perpendicu- A Rolled surface
B Direction of rolling
lar to the main axis of the material are often used for revealing
C Rolled edge
the following information:
D Planar section
5.3.1 Variations in structure from center to surface,
E Longitudinal section perpendicular to rolled surface
5.3.2 Distribution of nonmetallic impurities across the sec-
F Transverse section
tion,
G Radial longitudinal section
5.3.3 Decarburization at the surface of a ferrous material H Tangential longitudinal section
(see Test Method E 1077),
FIG. 1 Method of Designating Location of Area Shown in
5.3.4 Depth of surface imperfections, Photomicrograph.
E3–01 (2007)
are, based on technique used, three fundamental methods of surface. Ultrasonic cleaning may be effective in removing the
mounting specimens (see Section 9). last traces of residues on a specimen surface.
8.2 Any coating metal that will interfere with the subse-
7. Cutting of Metallographic Specimens
quent etching of the base metal should be removed before
polishing, if possible. If etching is required, when studying the
7.1 In cutting the metallographic specimen from the main
body of the material, care must be exercised to minimize underlying steel in a galvanized specimen, the zinc coating
should be removed before mounting to prevent galvanic effects
altering the structure of the metal. Three common types of
sectioning are as follows: during etching. The coating can be removed by dissolving in
cold nitric acid (HNO , sp gr 1.42), in dilute sulfuric acid
7.1.1 Sawing, whether by hand or machine with lubrication,
is easy, fast, and relatively cool. It can be used on all materials (H SO ) or in dilute hydrochloric acid (HCl). The HNO
2 4 3
with hardnesses below approximately 350 HV. It does produce method requires care to prevent overheating, since large
a rough surface containing extensive plastic flow that must be samples will generate considerable heat. By placing the clean-
removed in subsequent preparation. ing container in cold water during the stripping of the zinc,
7.1.2 An abrasive cut-off blade will produce a smooth attack on the underlying steel will be minimized. More
surfaceoftenreadyforfinegrinding.Thismethodofsectioning information may be found in Test Method A 90/A 90M.
is normally faster than sawing. The choice of cut-off blade,
NOTE 2—Picral etchant produces little or no galvanic etching effects
lubricant, cooling conditions, and the grade and hardness of
when used on galvanized steel.
metal being cut will influence the quality of the cut. A poor
NOTE 3—The addition of an inhibitor during the stripping of Zn from
choice of cutting conditions can easily damage the specimen,
galvanized coatings will minimize the attack of the steel substrate. NEP
producing an alteration of the microstructure. Generally, soft (polethylinepolyamine) or SbCl are two useful inhibitors.
materials are cut with a hard bond blade and hard materials
8.3 Oxidized or corroded surfaces may be cleaned as
with a soft bond blade. Aluminum oxide abrasive blades are
described in Appendix X1.
preferred for ferrous metals and silicon carbide blades are
preferred for nonferrous alloys. Abrasive cut-off blades are
9. Mounting of Specimens
essential for sectioning metals with hardness above about 350
9.1 There are many instances where it will be advantageous
HV. Extremely hard metallic materials and ceramics may be
to mount the specimen prior to grinding and polishing. Mount-
more effectively cut using diamond-impregnated cutting
ing of the specimen is usually performed on small, fragile, or
blades. Manufacturer’s instructions should be followed as to
oddly shaped specimens, fractures, or in instances where the
thechoiceofblade.Table1liststhesuggestedcutoffbladesfor
specimen edges are to be examined.
materials with various Vickers (HV) hardness values.
9.2 Specimens may be either mechanically mounted,
7.1.3 Ashear is a type of cutting tool with which a material
mounted in plastic, or a combination of the two.
in the form of wire, sheet, plate or rod is cut between two
9.3 Mechanical Mounting:
opposing blades.
9.3.1 Strip and sheet specimens may be mounted by binding
7.2 Othermethodsofsectioningarepermittedprovidedthey
orclampingseveralspecimensintoapackheldtogetherbytwo
do not alter the microstructure at the plane of polishing. All
end pieces and two bolts.
cutting operations produce some depth of damage, which will
9.3.2 The specimens should be tightly bound together to
have to be removed in subsequent preparation steps.
prevent absorption and subsequent exudation of polishing
8. Cleanliness
materials or etchants.
9.3.3 The use of filler sheets of a softer material alternated
8.1 Cleanliness (see Appendix X1) during specimen prepa-
with the specimen may be used in order to minimize the
ration is essential. All greases, oils, coolants and residue from
seepage of polishing materials and etchants. Use of filler
cutoff blades on the specimen should be removed by some
material is especially advantageous if the specimens have a
suitable organic solvent. Failure to clean thoroughly can
high degree of surface irregularities.
prevent cold mounting resins from adhering to the specimen
9.3.4 Filler material must be chosen so as not to react
electrolytically with the specimen during etching. Thin pieces
TABLE 1 Cutoff Blade Selection
of plastic, lead, or copper are typical materials that are used.
Hardness HV Materials Abrasive Bond Bond Hardness
Copper is especially good for steel specimens since the usual
up to 300 non-ferrous (Al, Cu) SiC P or R hard
etchants for steels will not attack the copper.
up to 400 non-ferrous (Ti) SiC P or R med. hard
9.3.5 Alternatively, the specimens may be coated with a
up to 400 soft ferrous Al O P or R hard
2 3
layer of epoxy resin before being placed in the clamp in order
up to 500 medium soft ferrous Al O P or R med. hard
2 3
up to 600 medium hard ferrous Al O P or R medium
2 3
to minimize the absorption of polishing materials or etchants.
up to 700 hard ferrous Al O P or R&R med
...
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