Published: Jan 1953
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The term metallography is not confined to the visual or microscopical examination of metals but may be defined as the study of the internal structure of metals and alloys and of its relation to their composition and to their physical, chemical, and mechanical properties. But this paper is concerned only with the microscopical examination of properly prepared metallic specimens. Microscopical examination is perhaps the most fruitful of the methods of investigation employed in the systematic study of metals and their alloys. Its use for metallic specimens probably originated as the examination of a fractured surface with a magnifying glass. As far back as 1665, Robert Hooke described in his “ Micrographia” (1) the formation of lead crystals during the freezing of a lead silver alloy as observed with a magnifying glass and drew the magnified image of the surface of a polished steel razor blade. In 1772 Réaumur (2) published his microscopic examination of fractured surfaces of steel and white cast iron and, based on his observations, he proposed a method of distinguishing between irons subjected to different thermal treatments. However, the microscopic examination of fractured surfaces proved to be a very restricted field unsuited for systematic study and it was not until about 1808 that Widmanstatten (3) opened the way to a better method by his discovery that certain meteorites, when cut and polished, developed a characteristic structure on being oxidized by heating in air or when etched with acids. Since magnification was not needed to see the Widmanstatten figures, the method was not extended to metals having finer structures, and metallography made no further progress for many years. One of the earliest metallographic examinations was made by Paul Annosow (4), who in 1841 examined with a microscope the polished and etched surfaces of oriental damascened steel blades.
Vilella, J. R.
United States Steel Corp., Kearny, N. J.