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.
A type 348 stainless steel in-pile tube 2 2 2 irradiated to a fluence of 3 x 10" n/cm, E > lMeV (57 dpa) , was destructively examined. The service had resulted in a maximum total creep of 1.8% at the high fluence. The metal temperature ranged between 623 and 652 K, hence the thermal creep portion of the total was negligible. Total creep was greater' than had been anticipated from creep data for austenitic stainless steels irradiated in other reactors. The objectives of the destructive examination were to determine the service-induced changes of mechanical and physical properties, and to assess the possibility of adverse effects of both these changes and the greater total creep on the prospective service life of other tubes, Measured bowing (0.51 mm) was correlated with a structural model. Post irradiation measurements included immersion density, fracture toughness, tensile strength and ductility, and creep-rupture strength. A reduction i:i fracture toughness due to irradiation creep was apparent.
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Uniaxial fatigue properties from tests at 400, 500, 600, and 700 C on Type 304, 304L (Ti modified), and 316 stainless steel specimens irradiated at 450 C in sodium and 750 C in argon at fluences of 0.03 to 9.3×1021 n/cm2, E>0.1 MeV, are given and compared with control specimens. Material was tested in the annealed, cold-worked, and chilled-swaged-tempered condition, while primary controls received a pretest anneal of 1500 h at 750 C. The data at 400, 500, and 600 C are compared with proposed design curves for 18-8 steels. Some data on microstructural changes due to irradiation are given. A reduction in the fatigue life by a factor of less than 2.5 was found in the annealed material, which was attributed to irradiation damage. A beneficial effect on fatigue life of pretreatment by swaging was found after irradiation at 450 and 750 C for 2550 h.
The influence of hydrogen on the mechanical properties (ductility, fracture strength, and tendency towards delayed failure) was investigated for several irradiated pressure vessel steels. Included were ASTM A302B, A542, and HY-80 steel irradiated at fluences from 8×1018 to 4×1020 n/cm2, E > 1 MeV. Specimens from plate sections of these steels which had been quenched and tempered and some from A542 which were given prestrain and heat treatment modifications were prepared and tested. The effects of strength level from irradiation, heat treatment, and microstructure were thus determined. Reductions in ductility and true fracture strength occurred with increasing hydrogen content but were not extensive at strength levels less than 180 ksi in specimens containing 1 to 2 ppm hydrogen. This concentration, however, produced a marked effect on the ductile properties when the strength level was increased by irradiation hardening or heat treatment beyond this threshold range. Irradiation hardening increased the magnitude of the decrease in notched strength resulting from a given hydrogen content in all of the steels and conditions tested. Hydrogen induced delayed failure, however, did not occur to any large extent in HY-80, A302B, and A542 steel in the normal quenched and tempered condition even after irradiation to fluences in excess of 1020 n/cm2, E > 1 MeV, and hydrogen concentrations of up to 4 ppm.
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