Tensile Properties of Fast Reactor Irradiated Type 304 Stainless Steel

Abstract

Tension tests were performed on annealed Type 304 stainless steel specimens sectioned from Experimental Breeder Reactor-II (EBR-II) duct thimbles. The specimens had accumulated neutron fluences of up to 10.3 × 1022 neutrons (n)/cm2, E > 0.1 MeV (10.3 × 1026 n/m2, E ×16 fJ). Irradiation temperatures for the material tested ranged from 700 to 750°F (644 to 672 K). The tests were performed at temperatures of room temperature to 1400°F (1033 K), employing strain rates of 2 × 10-3 to 2/min (3.3 × 10-5 to 3.3 × 10-2/s). At test temperatures below 800°F (700 K), the strength increased with fluence until about 7 × 1022 n/cm2 (7 × 1026 n/m2), beyond which no further increase was observed. The elongation decreased with fluence, reaching levels as low as 0.5 percent uniform and 1.3 percent total elongation at 700°F (644 K). High-fluence failures below 800°F (700 K) occurred by transgranular channel fracture. At test temperatures above 1000°F (811 K), elongations were reduced to very low levels at high fluences (average total elongation (TE) = 0.03 percent). Extensive intergranular fracture at the high fluences produced the low ductility and resulted in failure of the specimens before reaching the strength characteristic of the true hardness of the material.

A void nucleation and growth based damage framework to model failure initiation ahead of a sharp notch in irradiated bcc materials

“…4(a). The nature of void activity within the grain is consistent with the experimentally observed 'zigzag' fracture (Chaouadi, 2008) or 'channel' fracture (Fish and Hunter, 1976). In other words, failure path is found to propagate along faceted interfaces of the crisscrossing dislocation channels.…”

“…Void nucleation, on the other hand, is dependent both on the material stress levels and the loading temperature. The void radius is much lower at 437 K than the higher loading temperatures, indicating a change in failure mechanism from ductile 'zigzag' fracture (Chaouadi, 2008) to limited ductility 'channel' fracture (Fish and Hunter, 1976) in the temperature range 437-550 K. Note that Δϒ het was assumed to be temperature invariant in these simulations. However, Δϒ het may be expected to increase with decrease in temperature, further lowering the rate of void nucleation and growth.…”

“…In the context of the present problem, heterogeneous void nucleation is of interest because localization of deformation along dislocation channels in irradiated materials leads to the formation of interfacial regions with plasticity mismatch within the grains. In regions of high stress concentration (e.g., ahead of a sharp notch or crack-tip), nucleation and growth of voids would presumably be promoted at such interfaces, ultimately leading to transgranular 'zigzag' fracture (Chaouadi, 2008) or 'channel' fracture (Fish and Hunter, 1976).…”