DOE OSTI2019
Ferritic-martensitic steel Grade 92, with Grade 91 as a reference, together with austenitic stainless steel (or Incoloy Alloy) 800H and its grain-boundary-engineered version 800H-TMP (Thermo-Mechanical Processing), is investigated in this project. A total of fifteen Grade 92 samples from two or three heats, four T91 samples from two heats, and six 800H and six 800H-TMP samples from one heat were selected, which were primarily irradiated in the Advanced Test Reactor (ATR) of Idaho National Laboratory (INL), with the rest in the High Flux Isotope Reactor (HFIR) of Oak Ridge National Laboratory (ORNL), BOR-60 of Russia, and Phénix reactor of France. The samples were irradiated in the temperature range of 241 to 720°C and a dose range of 1.28 to ~70 displacements per atom. All the INL and ORNL samples and part of the LANL (Los Alamos National Laboratory) samples have been received at the Irradiated Materials Examination and Testing (IMET) hot cell facility. The selected ORNL samples include six Grade 92 and two 800H samples, which were irradiated in the HFIR to 0.46–14.66 dpa at 400 to ~720°C. The Grade 92 is an optimized heat and named as G92-2b. The two 800H samples have one sample as the standard solution-annealed condition and the other sample as a TMP condition with a maximized fraction of low-Σ coincidence site lattice (CSL) boundaries. Tensile test of the G92-2b samples were conducted at room temperature in the IMET hot cell. The lower temperature irradiation at 400–496.7°C to 0.52–14.66 dpa resulted in minimal changes in tensile properties. However, the higher temperature irradiation at ~683.3–720°C to 0.46–14.63 dpa tended to reduce yield and tensile strength by about –136 to –311 MPa and plastic elongation by –1 to –3% with the increasing dose. The 800H and 800H-TMP samples were tensile-tested at their irradiation temperature 580°C in the IMET hot cell, which showed >40% increase in yield and tensile strength with nearly 9% reduction in elongation for 800H-TMP compared with 800H. Three of the G92-2b samples, i.e., GB04 (7.44 dpa at ~490°C), GB05 (14.66 dpa at 496.7°C), and GB12 (14.63 dpa at ~720°C), were examined at the LAMDA for Vickers hardness measurements and microstructural characterization by SEM and TEM. Vickers hardness was successfully measured on GB12, which was reduced by is – (112.4 ± 12.3) HV1 from the control sample. However, the Vickers hardness measurements were failed on GB04 and GB05 because the samples were polished too thin to prevent the interference from the substrate (epoxy). The other half of the GB04 and GB05 will be polished for the hardness measurements, as well as nanoindentation studies. Fractography by SEM indicated increased numbers of ductile dimples (or voids) with the increasing irradiation dose, while significantly increased numbers and sizes of dimples with the increasing irradiation temperature. TEM characterization exhibited the presence of Cr 23 C 6 , VN, and Laves precipitates at boundaries and matrix, which showed pronounced precipitate-dislocation interactions (pinning effect). Dense dislocations but limited dislocation loops were observed in the samples, which noticeably reduced in GB12. Additionally, some tiny partially amorphized spherical domains were observed in GB12, which had a normal body-centered cubic lattice parameter of 9Cr steels at the surround regions but ~11% smaller than the lattice parameter of the matrix away from the amorphized spherical domains. Further characterization will be pursued to clarify the new findings.
22 GENERAL STUDIES OF NUCLEAR REACTORS↗