Effect of temperature on apparent crack arrest toughness of Eurofer97 measured by a newly developed small specimen test technique

Neutron embrittlement of in-core and out-of-core components made of ferritic steels is one of the key parameters limiting the life of power plants. Owing to the small volume of available irradiation facilities and the limited number of neutron-irradiated specimens, techniques to measure initiation fracture toughness with small specimens have been developed over the years. Although arrest toughness is of equal importance regarding safety assessment, the emphasis has been put on the effect of specimen size on initiation toughness and only a few small specimen test techniques can be found for arrest toughness measurements. The objective of the current work was to develop an experimental technique for measuring the apparent arrest toughness of ferritic steels with miniaturized specimens. Small cantilevers made of the 9Cr Eurofer97 equiaxed ferritic steel were produced with a brittle thin laser-treated layer, which enables crack initiation. The cracks were successfully arrested in the more ductile equiaxed ferritic matrix in a series of tests that were carried out from -123°C to room temperature with different test configurations. The mechanical tests showed that brittle fracture could be triggered and stopped inside the specimen with a width of 2 mm over a temperature range of more than 100°C. An apparent arrest toughness was calculated and its temperature dependence was related to the plastic work dissipated by a propagating crack.