IRRADIATION EMBRITTLEMENT OF A LOW ALLOY STEEL INTERPRETED IN TERMS OF A LOCAL APPROACH OF CLEAVAGE FRACTURE

Abstract— One heat of A 508 steel is investigated in both the unirradiated and the irradiated condition to determine the variation of the fracture toughness with temperature and specimen thickness. CT type specimens with three thicknesses B (12.5, 25 and 50 mm) are used. Two fluence levels (3·10¹⁹ and 8·¹⁹ n/cm²)( E < 1 MeV) are investigated. It is shown that the fracture toughness is a decreasing function of both specimen thickness and temperature. A model developed previously by Beremin is used to interpret the results. Axisymmetric notched specimens are tested to determine the factors used in the statistical approach of cleavage fracture. It is confirmed that the Beremin model is able to account for the large scatter in fracture toughness observed at a given temperature on the unirradiated material. The specimen thickness effect is also reasonably well interpreted by the model. The irradiation embrittlement can be explained by assuming that the cleavage fracture resistance is not modified by irradiation and by taking into account only the variations of yield strength with irradiation and test temperature.