Influence of Irradiation on the Creep/Fatigue Behavior of Several Austenitic Stainless Steels and Incoloy 800 at 700 C

Abstract

Results from elevated temperature-strain controlled fatigue and constant-strain-rate tensile tests conducted on specimens of stainless steel Types 304, 304L (titanium modified), 316, as well as Incoloy 800 are reported. Specimens were irradiated to fluences of 0.4 to 5 × 1022 n/cm2, E>0.1 MeV at 700 to 750 C (1292 to 1382 F), while the postirradiation test temperature was maintained at 700 C. Reductions in tensile ductility and fatigue life occurred, with reductions in fatigue life ranging from factors of approximately 1.5 to 2.5 for the stainless steels and up to 35 for Incoloy 800 in comparison with the thermal controls. Comparisons are made between actual irradiated fatigue behavior and predictions based on several semi-empirical methods using irradiated tensile data. These methods generally provided good estimates of the irradiated fatigue behavior of these materials. Introducing tensile hold times into the fatigue cycles of irradiated and unirradiated Type 316 stainless steel resulted in substantial reductions in the fatigue life of this material. However, for tensile hold times in excess of 0.1 h a tendency towards saturation of the hold-time effect was found in both the irradiated and unirradiated material. Creep and fatigue damage for Type 316 stainless was determined and summed linearly. This total damage was found to be a function of strain range, duration of tensile hold time, and irradiation condition for Type 316 stainless steel.

The effects of neutron radiation on nickel-based alloys

“…This suggests that the intragranular carbides are trapping boron and/or helium, preventing grain boundary embrittlement. Further evidence of helium trapping on TiC precipitates was presented by Harman 95 on Alloy 800 using incremental Ti additions. An optimised Ti content of 0.1 wt-% resulted in the optimum post-irradiation creep-rupture ductility, the reasons behind which, although speculative due to no characterisation being conducted, were a fine distribution of intragranular Ti-rich precipitates, trapping helium.…”

“…The composition, morphology, size, distribution, matrix/precipitate interface and stability of said precipitates will dictate whether they retard or enhance irradiation-induced swelling. 5,94,95 One possible way by which precipitates may retard swelling is through acting as sinks for point defects, preventing the coalescence of vacancies into voids. Similarly, a high number density of precipitates may be used to trap helium on precipitate/matrix interfaces, 94 thus preventing helium bubble formation and stabilisation of voids.…”

“…The composition, morphology, size, distribution, matrix/precipitate interface and stability of said precipitates will dictate whether they retard or enhance irradiation-induced swelling. 5,94,95…”

Fatigue Reliability Analysis Method of Reactor Structure Considering Cumulative Effect of Irradiation

“…However, the effect of irradiation is not generally considered in fatigue analyses of reactor structures. Some studies have carried out fatigue tests under different irradiation test conditions but obtained different (even contradictory) test conclusions [ 16 , 17 , 18 , 19 ]. Under certain irradiation test conditions, the fatigue life of the sample without irradiation is 1.5–2.5 times that of the sample with irradiation [ 16 , 17 ].…”

“…Some studies have carried out fatigue tests under different irradiation test conditions but obtained different (even contradictory) test conclusions [ 16 , 17 , 18 , 19 ]. Under certain irradiation test conditions, the fatigue life of the sample without irradiation is 1.5–2.5 times that of the sample with irradiation [ 16 , 17 ]. However, Zhong [ 18 ] found that the fatigue life of an irradiated sample was three times greater than that of a non-irradiated sample.…”