M EDesignation: E 3 – 95
An American National Standard
Standard Practice for
Preparation of Metallographic Specimens1
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. 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.
1.1 The primary objective of metallographic examinations
is to reveal the constituents and structure of metals and their alloys by means of the light 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 problems.
3. Signiﬁcance and Use
3.1 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.
3.2 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.
3.3 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.
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, 1984.
4. Selection of Metallographic Specimens
4.1 The selection of test specimens for metallographic
examination is extremely important because, if their interpretation is to be of value, the specimens must be representative of the material that is being studied. The intent or purpose of the metallographic examination will usually dictate the location of the specimens to be studied. With respect to purpose of study, metallographic examination may be divided into three classiﬁcations: 4.1.1 General Studies or Routine Work—Specimens from
locations that are most likely to reveal the maximum variations within the material under study should be chosen. For example, specimens should be taken from a casting in the zones wherein maximum segregation might be expected to occur as well as
specimens from sections where segregation should be at a
minimum. In the examination of strip or wire, test specimens should be taken from each end of the coils.
4.1.2 Study of Failures—Test specimens should be taken as
closely as possible to the fracture or to the initiation of the failure. Before taking the metallographic specimens, study of the fracture surface should be complete, or, at the very least, the fracture surface should be documented. Specimens should
be taken in many cases from a sound area for a comparison of structures and properties.
4.1.3 Research Studies—The nature of the study will dictate specimen location, orientation, etc. Sampling will usually be more extensive than in routine examinations.
4.2 Having established the location of the metallographic
samples to be...
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