Local Fracture Toughness Evaluation of 316LN Plate at Cryogenic Temperature

Within the frame work of the VAMAS TWA 17 activity, J evaluation on tensile test (JETT) was performed as an international round robin test. 316LN plate with 30 mm thickness was supplied as a common test material, but it contained irregular microstructure around the center of the plate thickness supposed to be generated during the rolling process. The fracture toughness at 4.2 K according to ASTM standard was invalid because of crack front shape requirement. However, JETT showed the lower toughness at the midsection than that at the near surface part. From this result, it was clarified that the JETT has a potential to evaluate local fracture toughness. Since the material showed serrated deformation during the JETT at cryogenic temperature, the evaluated toughness scattered rather widely, and stiffness of testing machine would affect the results.