ELEVATED TEMPERATURE IRRADIATION HARDENING IN AUSTENITIC STAINLESS STEEL

The nature and magnitude of radiation hardening in an 18-8 type austenitic stainless steel were investigated after a high neutron exposure (1.4 × 1022 n/cm2, E > 0.18 MeV) near one-half the absolute melting temperature (532°C). Transmission electron microscopy was used to reveal substructural features prior to tensile testing over the temperature range 23-871°C. The irradiation produced a substructure consisting of Frank sessile loops about 400 Å in diameter and 3.7 × 1015/cm3in density and polyhedral cavities approximately 150 Å in diameter and about 2 × 1014/cm3 in density. Annealing for one hour at 593°C induced the Frank sessile loops to transform into perfect dislocation loops which, in turn, migrated and interacted to form a complex dislocation network. Annealing at progressively higher temperatures resulted in simultaneous cavity and network annihilation at 816°C. After irradiation, the yield strength follows a thermally-activated temperature dependency at test temperatures less than Tm/2. The athermal yield stress component is attributed to the strengthening expected from the Frank sessile loops. Above Tm/2, the loops are annihilated and a corresponding decrease in yield strength occurs. However the strength does not approach the unirradiated control value as the loop density tends to zero but remains at a value which is consistent with the experimentally-determined density of cavities. Full recovery of the yield strength is observed at 816°C when both the dislocations and cavities are annihilated. © 1968.