Fracture toughness characterization in the lower transition of neutron irradiated Eurofer97 steel

This research investigated the evolution of tensile, hardness, and fracture properties of Eurofer97 tempered martensitic steel following neutron irradiation. The irradiation-hardening was measured with Vickers hardness tests on broken parts of sub-sized compact tension specimens as well as with tensile tests deformed at room temperature. The fracture toughness was measured with pre-cracked sub-sized 0.18T compact tension specimens. Two specimen sets were irradiated up to a nominal dose of about 0.35 dpa at two different temperatures, 423 and 623 K, in the experimental reactor at AEKI-KFKI in Budapest. The median fracture toughness–temperature curve K(T) was characterized in the lower to middle transition region for each irradiation condition using the master-curve method. The irradiation-induced temperature shifts of K(T) were determined by calculating the reference temperature T0 at which the median toughness is 100 MPa m1/2. A significantly larger shift was determined for Eurofer97 irradiated at 423 K than at 623 K. Indeed, an upper shift of 98 K was found for the 423 K irradiation while only 50 K was measured for the 623 K. On the one hand, that observation reflects the difference in the irradiation-hardening following those two irradiation temperatures. On the other hand, when compared with other published data, the ΔT0 shift at 623 K irradiation was found to be greater than expected for the corresponding irradiation-hardening. Thus, it was suggested that non-hardening embrittlement mechanisms start to operate around 623 K.