Stress corrosion cracking behavior and mechanism of scratched Alloy 690TT in lead-containing caustic solution

The stress corrosion cracking (SCC) behavior and mechanism of scratched Alloy 690TT in lead-containing caustic solution at different time periods were studied by C-ring test method. Results indicated that the PbSCC in the scratch area initiated at the accumulation slope and narrow gap position in the plastic accumulation zone, and the crack first propagated along the direction almost parallel to the side of the scratch groove. The crack propagation mode was dominated by transgranular SCC (TGSCC), and then transformed into intergranular SCC (IGSCC), both TGSCC and IGSCC exhibited similar oxidation and PbSCC mechanisms. The PbSCC in the scratched area still followed the film-rupture/slip-dissolution mechanism, but lead significantly accelerated the initiation and propagation of SCC. The mechanism of PbSCC in the scratch area, including oxide film-rupture, preferential oxidation of Cr and Fe (de-alloying), and lead promoted the selective dissolution of Cr from the oxide film. Moreover, there was a significant trend change in crack propagation depth at 1500 h, which was related to the macro-micro structure of the scratch area and the cracking mode of PbSCC.