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(of a metal), the structure of a metal that is visible visually or under a magnifying glass (that is, under magnification of up to 25 X). The macrostructure is studied in flat samples, called templates, cut from an item or blank, and also on the fracture surfaces of articles. To reveal the surface structure of a template, it is polished carefully and then etched with solutions of acids or alkalies.
The study of the macrostructure reveals discontinuities in the metal (cavities, porosity, gas bubbles, stratification, and fissures), distribution of impurities and nonmetallic inclusions, shape and distribution of crystallites (grains) in various parts of the item, and sometimes even the structural features of individual grains of the metal. Studies of the macrostructure lead to conclusions on the quality of initial materials and the correctness of the conduct of casting, pressure working, and welding processes. In some cases the quality of metals is characterized by the type of fracture, which makes possible determination of the path of the plane of fracture (through the body or along the grain boundaries) and of the causes of fracture.
V. IU. NOVIKOV