| The stress corrosion cracking (SCC) condition for Alloy 600 was determined for various stress modes: constant-strain standard C-ring, and indentation, used to localize cracks for interrogation with x-ray techniques such as micro Laue diffraction (MLD). The SCC cracks nucleated on both the indentation edge, where finite element analysis showed that the maximum residual tensile stresses lie, and the surface in tension (bulge) on 150-kgf conically indented mill-annealed specimens (0.02 wt% C) in de-aerated solution of 10% caustic at 150 mV RE (pseudo-reference: A600), 315°C for 48 hr. On the C-rings, the cracks nucleated at the lateral outer surface of apex, where maximum tensile stresses lie, in less than 12 hours, and propagated into the cross section. Also, corrosion tests on as-received A600 30-min ZrO2 surface mechanical attrition treated (SMAT) specimens suggested an intergranular attack type of behavior in 50% caustic at 210 mVRE (pseudo-reference: A600), 280°C for 24 hr. |
