Abstract
Hydrogen permeation measurements have been carried out on a super 13% Cr martensitic stainless steel over a range of temperatures (5°C to 70°C) under cathodic charging conditions. Trapping in this steel is predominantly reversible and is ascribed to the interface between retained austenite and the martensite phase. This is in contrast with conventional 13% Cr steel (AISI 410 [UNS S41000]) for which irreversible trapping at carbides was important. Comparison of effective diffusivities for each material at room temperature, calculated using trapping models, shows that the diffusivity for super 13% Cr steel is significantly higher for low hydrogen uptake, while that for Type 410 steel is higher under more severe charging conditions. The results highlight the importance of quoting the charging conditions when comparing effective diffusivities. For a constant applied cathodic protection potential, the hydrogen uptake increased with temperature, but the concentration of trapped hydrogen did not vary much over the range tested because of the competing effect of trap occupancy.
