Fracture Toughness and Tensile Behavior of Incoloy 908

Abstract

Tensile properties of Incoloy^® alloy 908^* conduit material for the ITER Model Coil were determined at cryogenic temperatures (4 K, 77 K) and room temperature under two process conditions: (1) as received; and (2) compacted, bent, re-straightened, and heat treated for 650°C for 240 hours in vacuum. Fracture toughness for the two process conditions were also measured at room temperature and 4K by the single specimen J-integral test technique. J-integral results were interpreted by two standards, E 813–89 and E 813–81.

Tensile yield and ultimate strength increase with decreasing temperature. Specimen orientation has little influence on yield and ultimate tensile strength. According to E 81389, the fracture toughness, K_Ic, of the base metals in the heat-treated condition is approximately 194 MPa√m at 4K in the transverse direction and 192 MPa√m at room temperature in the longitudinal direction. According to E 813-81, the fracture toughness values are 174 and 164 MPa√m for the same conditions. According to this standard, more data points are valid. Overall the E 813-81 results are more conservative than those of the E 813-89 standard. Preliminary data suggest that conduit and plate fracture toughness data are comparable, although plate toughness seems slightly lower. Further evaluation of this relationship is in progress. However, it appears that basing life predictions on plate material properties would provide conservative values.