Fracture toughness, thermo-electric power, and atom probe investigations of JRQ steel in I, IA, IAR, and IARA conditions

The International Atomic Energy Agency has sponsored a number of studies involving a specific plate of A533 grade B class 1 steel designated heat JRQ. In this cooperative study between the Paul Scherrer Institute (PSI) and the Heavy-Section Steel Irradiation Program of Oak Ridge National Laboratory (ORNL), groups of Charpy impact, tensile, and precracked Charpy specimens of the JRQ plate were irradiated by PSI to four different fast neutron fluences [from 0.39 to 5.0 × 10²³ n/m² (>1 MeV)] in a test reactor. Additional specimens were given a post-irradiation thermal annealing treatment at 460°C for 18 h when 50 % of the target fluence was reached, followed by reirradiation to the same target fluences for the four groups of irradiated specimens. Additionally, ORNL thermally annealed some of the reirradiated specimens, as well as some of those in the irradiated only condition. Charpy impact, tensile, fracture toughness, and hardness tests have been performed to evaluate material response in the various conditions and to compare with the unirradiated material. Additionally, thermo-electric power experiments have been conducted by PSI, while atom probe tomography evaluations have been conducted by ORNL. Except at the highest fluence, the results show that the material given an intermediate annealing treatment exhibited irradiation-induced transition temperature shifts about the same as those that were only irradiated. However, the upper-shelf energies were generally higher and the yield strengths were generally lower for the reirradiated groups. The intermediate thermal annealing resulted in less reirradiation embrittlement of fracture toughness than Charpy impact toughness, while annealing after reirradiation resulted in significant increases in Charpy upper-shelf energy above that in the unirradiated condition. Irradiation-induced and IAR Charpy impact transition temperature shifts exhibit a nearly linear correlation with Seebeck coefficient in the I and IAR conditions. ORNL has also sent additional specimens from I, IA, IAR, and IARA test of JRQ for additional TEP testing. After irradiation, a high number density of ultrafine Cu-, Mn-, Ni-, Si-, and P-enriched precipitates were observed by atom probe tomography. Phosphorus segregation to dislocations was also observed. A significantly lower number density of larger Cu-, Mn-, and Ni- enriched precipitates was observed after the second annealing treatment.