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in archaeology, the name for chips struck from a piece of flint or flint core by human hands. Flakes varied in shape and size. During the Stone and Bronze ages, tools, including knives, were made from flakes.
an internal crack in forged or rolled steel products, and sometimes ingots and cast articles, that markedly detracts from the desired mechanical properties of the steel. In pickled micro-sections, flakes are identified as hairline cracks; in the fracture testing of hardened specimens, flakes are oval, crystalline spots of a silvery white color distinguishable from the primary gray mass of the fracture. The steels most susceptible to flake damage are alloyed and carbon martensitic and pearlitic steels used for structural members, bearings, armor, and rails. Defects of this type are not found in austenitic or carbide steels (stainless and high-speed steels).
The principal cause of the formation of flakes is the presence of excessive hydrogen, and the mechanism most likely responsible is adsorption of hydrogen on the surfaces of microscopic irregularities, which reduces surface energy and makes destruction easier. Flakes originate in zones with heightened adsorption of hydrogen. The formation of such zones stimulates internal tensile stresses that arise in the steel during structural transformations, plastic deformation, and uneven cooling. Flake development is also promoted by a reduction in the metal’s resistance to destruction in places where stresses have concentrated near accumulations of defects of the crystal lattice, as well as by concentrations of nonmetallic inclusions and segregated inhomogeneities. Flakes may be controlled by thermal treatment of the parts under special conditions and by subjecting the molten steel to a vacuum, which reduces the hydrogen content to a safe level.
REFERENCESDubovoi, V. la. Flokeny v stali. Moscow, 1950.
Moroz, L. S., and B. B. Chechulin. Vodorodnaia khrupkost’ metallov. Moscow, 1967.
V. L. SAFONOV and M. L. BERNSHTEIN