For understanding the improvement of intergranular stress corrosion cracking (IGSCC) propagation in grain boundary engineering (GBE)-processed metals exposed to a simulated pressurized water reactor (PWR) environment, characteristics of the grain boundary network of 316L stainless steel before and after GBE were investigated and compared, including proportions both in length and in number of ∑3ⁿ boundaries, sizes, and topology of grain clusters (or twin-related domains), and connectivity of random boundaries. The term through-view random boundary path (TRBP) was proposed to evaluate the random boundary connectivity. A TRBP is a chain of end-to-end connected crack-susceptible boundaries that passes through the entire mapped microstructure. The work provides the following key findings: (I) the length fraction of ∑3ⁿ boundaries was increased to approximately 75% after GBE, but the number fraction was only approximately 50%; (II) a connected non-twin boundary network still existed in the GBE sample due to the formation of grain clusters; (III) the GBE sample exhibited a higher resistance to IGSCC; and (IV) as the twin boundary fraction increased, the number of TRBPs decreased and the normalized length of the minimum TRBP increased monotonically, leading to a higher resistance to IGSCC.

Grain boundary engineering (GBE) via low strain tension and annealing was used to enhance the resistance to stress corrosion cracking of a 304 stainless steel. Electron backscattered diffraction (EBSD) analysis exhibited that the GBE steel had a higher fraction of low-∑ coincidence site lattice (CSL) boundaries, larger grain-clusters, longer twin boundary chains, and fewer paths of connected non-twin boundaries with a more zigzag shape. Slow strain rate tests in high-temperature water showed that the GBE steel performed better plasticity, higher tensile strength, and similar yield strength compared to conventional steel. The low fraction of random boundaries in GBE steel resulted in a lower frequency of intergranular crack initiation, and the zigzag paths of non-twin boundaries made the intergranular crack propagation more difficult.