Abstract
The influence of minor alloying platinum group metal additions on stress corrosion cracking (SCC) of austenitic stainless steels has been investigated in simulated pressurised water reactor environments. Crack propagation studies, employing tensile specimens precracked in acidified potassium tetrathionate and subsequently loaded in proving rings revealed that 1 wt-% ruthenium additions improved the resistance of 304 stainless steels to SCC. Analytical transmission electron microscopy was used to characterise crack tips and surface oxides after high temperature SCC tests. Enrichment of ruthenium and molybdenum within the dual oxide surface layers was observed in the ruthenium modified stainless steel, which is likely to have occurred during potassium tetrathionate pre-exposure and promoted intergranular SCC mitigation. Palladium additions (1 wt-%) showed no beneficial effects to SCC, and this was associated with the formation of second phases PdMn particles upon sensitisation, which decreased the availability of Pd.
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