The change of fracture toughness of martensitic steels after irradiation in SINQ target-3

Small bend specimens of martensitic steels T91, F82H and Optimax were irradiated in SINQ target-3 up to about 9 dpa in a temperature range of 100–250 °C. The single specimen method was used to determine the J-integral values. The specimens were tested in a temperature range from room temperature to 250 °C, mostly at irradiation temperatures. The results showed that the fracture toughness of the martensitic steels decreased with increasing irradiation dose. Specimens tested at the irradiation temperatures and 250 °C indicated that the fracture toughness of all three martensitic steels remained above 100 MPa m1/2. One T91 specimen irradiated to 4.3 dpa tested at room temperature was totally brittle and broke in the elastic deformation region. The fracture toughness value was only about 28 MPa m1/2, within the lower shelf of the fracture toughness. There was no obvious difference in the fracture toughness of the steels after irradiation.