Insights into stress corrosion cracking in scratched area of alloy 690TT steam generator tubes

To investigate the stress corrosion cracking behaviors and microscopic mechanism in a scratched area of alloy 690TT, the microstructures of typical cracks are systematically characterized. There is a severe structural mismatch at the interface between fine grain zone and severe deformation zone, and hence cracks tend to propagate continually along this interface. In addition, the scratching leads to fracture and displacement of carbides, which changes their morphologies and distribution. Carbides with small sizes are engulfed by the crack oxidation zone, while large carbides can change the propagation path, and thus the crack grows into the deformation layer.