Lead-induced stress corrosion cracking (PbSCC) initiation in alloy 690TT in caustic environment

Pb-Caustic Stress Corrosion Cracking initiation was studied on Alloy 690TT at 315 degrees C. Advanced electron microscopy techniques revealed that cracking mainly initiated intergranularly following the oxidation of Cr-rich grain boundary carbides. This finding explains the higher resistance to crack nucleation of the as-received surfaces compared to polished ones, because the grain boundaries of the ultrafine-grained near-surface layer were not decorated with carbides. It is also proposed that dislocation entanglements, typical of a cold-worked surface, attenuated the emission of dislocations at the surface. Once initiated, cracking continued due to Pb incorporation in the oxide, which weakened the passive layer and enhanced slip dissolution.

Automated summary

Pb-Caustic Stress Corrosion Cracking initiation was studied on Alloy 690TT at 315 degrees C. The cracking mainly initiated intergranularly following the oxidation of Cr-rich grain boundary carbides. The as-received surfaces showed higher resistance to crack nucleation compared to polished ones due to the absence of carbide decoration on the grain boundaries in the ultrafine-grained near-surface layer. Dislocation entanglements on the cold-worked surface attenuated the emission of dislocations at the surface. Subsequent cracking was caused by Pb incorporation in the oxide, weakening the passive layer and enhancing slip dissolution.