Role of Heat Treating on the Intergranular Stress Corrosion Cracking of Alloy 600

It has been recognized in Ni-base alloys that the grain boundary chemistry and its microestructural heterogeneities are important factors in the material environmental degradation. Therefore, in this study, we investigated the role of the heat treatments and the obtained microstructure in the IGSCC susceptibility of alloy 600 in environments of pressurized water reactors (PWR). The role of microstructure on the intergranular cracking resistance (IGC) of alloy 600 was also investigated using a modified wedge opening loading specimens which were annealed at 930, 800 and 600°C and also exposed to high purity water pressurized with hydrogen at 300°C. It was found the microstructure induce relatively low crack growth rates associated with the development of significant plastic deformation at the crack tip. In addition, some common features were found between the IGSCC performance and the pre-fatigue cracking conditions. For this purpose, the fatigue crack growth properties of this alloy were also evaluated using the ASTM E 606–92.