High-Temperature Helium Embrittlement of 316FR Steel

Abstract

The helium embrittlement behavior of 316FR austenitic stainless steel was investigated by a tensile test at 750 C using miniature tensile specimens, which were helium-implanted below 100 C up to 5, 30, and 100 appm using a cyclotron accelerator, and were post-implantation-annealed at 750C for 10 and 100 h. The helium-implanted specimens showed a fully intergranular fracture regardless of the helium concentration and annealing time. No microstructural changes in the as-implanted specimen up to 30 appm and formation of a small number of helium bubbles due to the post-implantation annealing were observed. The gradual release of the helium during the tensile test started after the yielding, and a sharp peak of the helium release was detected in the final fracture phase. The total number of helium atoms released was strongly dependent on the implanted helium concentration, rather than on the annealing time.

Overview of Intergranular Fracture of Neutron Irradiated Austenitic Stainless Steels

“…It is stated in [54] that, below 550 °C, the IG fracture of Type 316 neutron irradiated containing He was correlated with edge-to-edge He bubbles spacing closer than 8 nm and bubble diameter. At temperatures higher than 550 °C [54,55], IG fracture was observed regardless of He spacing. Recently [18], the grain boundary fractures were studied in room temperature He-ion irradiated 15%CW316L specimens using in-situ testing with micro-size tensile specimens FIB fabricated across grain boundaries.…”

Identifying Limitations of ASME Section III Division 5 For Advanced SMR Designs

“…Therefore, the dimensional changes due to irradiation creep is generally only of concern for high stress and high dose conditions or cases where void swelling is significant. Irradiation growth is a volume-conservative anisotropic distribution of strains without the presence of stress [42]. It is usually observed in anisotropic crystalline materials such as graphite and most prominent at low-to-intermediate irradiation temperatures [43].…”

Environmental creep-fatigue and weld creep cracking: a summary of design and fitness-for-service practices

“…Irradiation growth is a volume-conservative anisotropic distribution of strains without the presence of stress and introduces severe distortion. At high temperature, helium can accumulate at grain boundaries through diffusion or dragging by dislocations and may cause grain boundary embrittlement [75]. Some of the parameters that affect all the irradiation-induced phenomena are neutron fluence or dpa (displacements per atoms), dpa rate, temperature, stress, and lattice structure and composition of metal.…”