Grain boundary chemistry in irradiated stainless steel and its influence on environmental degradation

Radiation-induced segregation (RIS) of chromium, silicon and phosphorus and its influence on intergranular stress corrosion cracking (IGSCC) of stainless steel (SS) has been investigated. Material and irradiation effects on RIS to grain boundaries were studied using ion bombardment of fine-grained, sputter-deposited SS. Damage levels up to 10 dpa were produced in near-surface regions encompassing several grain diameters in depth. The resultant ''bulk'' damage promotes RIS of silicon and depletion of chromium at grain interfaces. Silicon enrichment and chromium depletion was highly localized to within 25 nm of the boundary in 316 SS heats as measured by analytical transmission electron microscopy. No significant grain boundary enrichment of phosphorus was observed in these heats even though heats contained very high levels of phosphorus in the bulk. Grain boundary chemistry effects on the IG corrosion and SCC of 316 SS have also been examined by varying phosphorus segregation and chromium depletion through controlled thermal treatments. 28 refs., 3 figs