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For a number of years, standards and code-writing bodies have been attempting to specify fracture toughness in terms of the Charpy V-notch rather than the Charpy keyhole test because various investigators have shown that V-notch test results correlate much better with service experience. However, the change to V-notch specifications has been deterred by uncertainty concerning the best criterion for establishing transition temperatures and the effect of strength and thickness on transition temperatures. Therefore, five steels covering a wide range of yield and tensile strengths (ABS-C: 39/63, A302-B: 56/88, HY-80: 81/99, A517-F: 121/134, and HY-130: 140/148) were tested as quarter-, half-, single-, and double-width (QW, HW, SW, and DW) Charpy V-notch specimens in the longitudinal and transverse directions and with through-thickness and surface notches. Transition temperatures were determined for various energy-absorption, lateral-expansion, and fracture-appearance criteria.
The results showed that energy-absorption criteria for determining transition temperature should increase with strength to ensure a constant notch ductility. Thus the best method for determining transition temperature was the direct measurement of lateral expansion. Of the lateral-expansion criteria evaluated, the 15 mil value agreed best with fracture-mechanics considerations.
The average increase in transition temperature was 60 F from QW to HW specimens, 26 F from HW to SW specimens, and 2 F from SW to DW specimens. This indication of maximum constraint for the SW specimen was not consistent with the effects produced when the standard V-notch was replaced with a fatigue crack. Consequently, the size of the Charpy test specimen that should be used for evaluating thick plates has not been established and requires additional study.
The effects of strength and thickness on transition temperature were much larger than the effects of testing direction, notch location, or notch acuity.
The results indicate that, of the various criteria for evaluating the Charpy V-notch impact-test performance of structural steels, lateral expansion is the best criterion for compensating for the important effects of steel strength and plate thickness. Moreover, its validity is supported by fracture-mechanics concepts.
steels, notch impact strength, tensile strength, notch toughness, ductility tests, ductile brittle transition, fracture toughness, fracture mechanics, evaluation, tests
Manager, Applied Research Laboratory, U.S. Steel Corp., Monroeville, Pa.