This paper studies the stress corrosion cracking (SCC) behaviour of Incoloy 800 in pure 10%NaOH and, respectively, 10%NaOH+0.33g/l NaCl solutions. Notched and un-notched C-ring specimens were tested in a static autoclave at 2600C and 50 bars. To evaluate the electrochemical behaviour of different metal/environment systems, the most important electrochemical parameters were calculated from polarization curves recorded between (�800)mVvsSCE and (+1200)mVvsSCE (scan rate 1mV/s), at 850C. It was emphasised that the presence of Cl- in caustic environment conducts to the decreasing of corrosion rate and corrosion current. Optical microscopy (OM) and scanning electron microscopy (SEM) revealed that the initiation mechanism and penetration depth of SCC cracks depend on the composition of the testing solution: in pure caustic solution, the SCC initiation is transgranular the SCC cracks propagated up to 120m, while in the presence of the Cl-, the SCC cracks started from the pits formed on the samples surface and the SCC depth is shorter than in the pure caustic solution (only up to 20m). X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS) analyses were used to identify the composition of the oxide layer build-up on the surface of the specimens exposed in autoclaves. The results indicate that, in the presence of the Cl- anions, the spinel oxide NiCr2O4 is formed in a bigger amount. Due to this compound formation, a greater SCC resistance of Incoloy 800 was observed.
In situ synchrotron X-ray tomography of 304 stainless steels undergoing chlorine-induced stress corrosion cracking