Grain boundary composition and irradiation-assisted stress corrosion cracking resistance in Type 348 stainless steel

Scanning transmission electron microscopy (STEM) analyses, in-reactor swelling mandrel tests, and laboratory constant extension rate tensile (CERT) tests were conducted on nine custom type 348 (UNS S34800) stainless steel (SS) alloys in an attempt to correlate grain boundary composition with irradiation-assisted stress corrosion cracking (IASCC) resistance. Phosphorus (P) enrichment showed the best correlation with in-reactor test results, and chromium (Cr) depletion showed the best correlation with laboratory results. Silicon (Si) and P enrichment were found to depend quantitatively on the bulk concentrations of these elements. The amount of Cr depletion seemed dependent at least partially on the amounts of Si and/or P enrichment. Si and P enrichment and Cr depletion were suppressed by higher carbon (C) contents, such as that present in commercial-purity type 348 SS