Effect of deformation on stress corrosion behavior of nuclear grade austenitic stainless steel

The stress corrosion cracking (SCC) behavior of the cold-deformed twisted tubing (TT) fabricated from nuclear grade austenitic stainless steel is investigated. Finite element simulations combined with hardness tests identified localized strain concentration in the convex regions of cold-deformed TTs. These areas exhibited dense deformation twins with high kernel average misorientation values, whose spatial distribution matched the predicted strain concentration zones. Slow strain rate tensile tests conducted in high-temperature pressurized water and argon environments show that cold-deformed TTs demonstrated SCC characteristics, displaying typical quasi-cleavage crack features with river patterns on fracture surfaces. While the original material showed minimal SCC susceptibility, further analysis using focused ion beam-transmission electron microscopy and transmission Kikuchi diffraction on longitudinal fracture sections revealed that severe plastic deformation induced refinement of deformation twins. During the initial stage of SCC, hydrogen-assisted SCC nucleation and propagation occurred preferentially along dynamically recrystallized nanocrystalline grain boundaries. In the rapid propagation stage, strain localization and reduced hydrogen effects redirected crack paths to incoherent interfaces between nanocrystals and deformation twins. Notably, the deformation twins exhibited inherent resistance to SCC, attributable to the coherent structural arrangement and minimal stress concentration characteristics.