Fracture toughness of European reference RAFM steel EUROFER97

RAFM steel EUROFER97 is the European reference structural material for the ITER Test Blanket Module (TBM) and the DEMOnstration fusion power plant. Fracture toughness belongs to the key mechanical properties needed for the assessment of the structural integrity of the nuclear components under monotonic mechanical loading. Aiming at the support of implementation of EUROFER97 in RCC-MRx by F4E, the EUROfusion MAT-TBM group carried out fracture-mechanical characterization of the third and fourth batch of EUROFER97 in a temperature window between RT and 550°C. The resistance curve methodology implying the Unloading Compliance (UC) measurement according to ASTM E1820 standard has been proposed as the reference approach for the determination of the crack resistance curve and elastic-plastic fracture toughness J$_{Ic}$. The application of the UC method, however, yielded so called ‘negative crack growth’ phenomena at the initial loading stage prior to onset of physical crack growth, which was corrected by appropriate offsetting the J-R curve. Furthermore, the compliance was found to be largely scattered particularly at elevated temperatures. ... mehrThe observed apparent negative crack growth and compliance scattering prevented the elastic plastic fracture toughness J$_Q$ from being qualified as the test standard conform J$_{Ic}$. Fractographic analysis revealed complex, 3D growth of ductile cracks. To back up the resistance curve J-R results, the Normalization Data Reduction Technique and Basic Procedure have been implemented. Significant quantitative differences have been observed both in the J-R behavior and J$_Q$ values between the third and fourth batch of EUROFER97, even though both batches exhibited high toughness in the investigated temperature range. The temperature dependence of the toughness are discussed and the toughness values obtained by different methodologies and different labs are compared systematically.