Is used to reveal the heterogeneity of metals and alloys. Metallographic specimens (See Micro Etching) provide the necessary detailed information about specific localities but they cannot give data about variation from one place to another unless an inordinate number of specimens are taken.
Macroetching, on the other hand, will provide information on variations in;
1. Structure, such as grain size, flow lines, columnar structure, dendrites, and so forth;
2. Variations in chemical composition as evidenced by segregation, carbide and ferrite banding, coring, inclusions, and depth of carburization or decarburization.
The information provided about variations in chemical composition is strictly qualitative but the location of extremes in segregation will be shown. Chemical analyses or other means of determining the chemical composition would have to be performed to determine the extent of variation. Macroetching will also show the presence of discontinuities and voids, such as seams, laps, porosity, flakes, bursts, extrusion rupture, cracks, and so forth.
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