Effect of residual stresses on notch toughness of the tempered martensitic steel F82H-MOD

The effect on notch toughness of residual stresses introduced by pre-deforming double edge notched tensile specimens of the high-chromium reduced activation tempered martensitic steel F82H-mod was investigated. Residual elastic strains/stresses were introduced by pre-deformation in tension at room temperature up to different levels. Measurements of residual strains/stresses were performed by neutron diffraction using POLDI Materials Science Diffractometer at Paul Scherrer Institute in Switzerland. A good agreement between the calculated residual stresses by finite element modeling and the measured ones was found. The pre-deformed specimens were then tested up to fracture at −150 °C and compared with specimens tested without pre-deformation. The local fracture stress in the notch vicinity was determined from finite element simulations and compared with previously calibrated fracture stress on pre-cracked fracture specimens tested in the brittle to ductile transition region. The fracture stress of the double edge notched specimens was consistent with that of pre-cracked specimens. The effect of pre-deformation on ultimate fracture load was not found to be beneficial for the specimen geometry considered. This behavior was attributed to the broad stress distribution characteristic of notch with a peak location that does not lie in the compressive residual stress region near the notch root.