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V-notch Charpy slow-bend tests (see also Armstrong (1)) have been conducted over a range of temperatures, using three commercial structural steels representing the full range of commercial deoxidation practice, and a number of carbon-manganese steels containing 0.04 to 0.45 per cent carbon and 0.43 to 1.05 per cent manganese. The criteria used in evaluating slow-bend performance were (1) lateral expansion, (2) fracture appearance, and (3) temperature. In particular, attention was focused on the deformation, fibrosity, and temperature attending catastrophic crack propagation (sudden and complete fracture of the test specimen at maximum load). It was found that considerable plastic deformation occurs in the V-notch Charpy slow-bend bar even at temperatures resulting in 90 per cent crystallinity and catastrophic crack-propagation. By defining transition temperature as the highest temperature at which an initiating crack can propagate under action of the elastic-stress energy alone, that is, sudden and complete fracture of the test specimen at maximum load, and by noting the deformation occurring in specimens which fractured at maximum load, it was possible to differentiate between the deformation attending the crack initiation and crack propagation stages of fracture in slow bend.
Hartbower, Carl E.
Chief, Watertown Arsenal Laboratories, Watertown, Mass.