Radiation-and anneal-hardening of neutron-irradiated ferritic steels and α-iron

Abstract

Abstract Samples of low-alloy and low-carbon steels, and of α-iron containing 30, 70 and 270 ppm C were neutronirradiated at ambient temperatures, i.e. max 90°C for steels and max 40°C for α-iron. The doses varied from 5.5 × 1018 to 3.5 × 1019 neutrons/cm2. The mechanical properties were measured before and after irradiation and after post-irradiation annealing at temperatures up to 500°C. Maximum hardening was observed in steels after annealing between 100 and 250°C, and in α-iron, between 100 and 125°C. Using TEM the structure of nonirradiated, irradiated, anneal-hardened and recovered specimens was examined. It was concluded that radiation hardening, as well as anneal hardening was mainly due to invisible defects. The increase observed in the yield stress was found to be consistent with the hardening by dislocation loops of ∼20Å in diameter, which act as weak barriers. Radiation-anneal hardening of α-iron was interpreted on the basis of the ‘strengthening’ of radiation-induced defects by carbon atoms migrating above T irr. In steels, the processes involved are much more complex and are influenced by a number of metallurgical and irradiation parameters.