HYDROGEN DIFFUSIVITY MEASUREMENTS AND MICROSTRUCTURAL CHARACTERIZATIONS OF PRECIPITATION HARDENED STAINLESS STEEL

Sigalit Ifergane ^1,2 Eyal Sabatani ² Zehava Barkay ³ Velodia Ezersky ⁴ Benny Carmeli ² Ofer Beeri ² Noam Eliaz ¹

¹Department of Materials Science and Engineering, Tel Aviv University, Tel Aviv
²., Nuclear Research Center Negev, Beer-Sheva
³The Wolfson Applied Materials Research Center, Tel Aviv University, Tel Aviv
⁴Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer-Sheva

Advanced precipitation hardened stainless steel Custom 465^® is characterized by a combination of high strength and good corrosion resistance. h-Ni₃Ti precipitates and reverted austenite evolution during aging of the steel was characterized by Environmental Scanning Electron Microscopy (ESEM), Electron Backscattered Diffraction (EBSD), X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM).

The hydrogen diffusivity in the steel was evaluated by electrochemical hydrogen permeation tests. The permeation setup and the experimental procedures were following Devanathan and Stachurski double-compartment cell design and test procedures. The specimen, a steel membrane (120-200 mm thick), was placed between the two electrochemical compartments. The membrane was galvanostatically polarized on its cathodic side, to force hydrogen evolution. Part of the hydrogen atoms are absorbed in the steel, diffuse through the membrane and reach the anodic side. The anodic side is potentiostatically biased, such that hydrogen diffusing out is oxidized. The current due to hydrogen oxidation was recorded continuously over time. Specimens in three thermo-mechanical conditions were examined: solution annealed (SA), aged H900 (480ºC/4 hour), and H900 following by 0.2% deformation.SA samples exhibit 10 times higher apparent diffusion coefficient than H900 conditioned samples. Different trap types were recognized in the H900 condition samples and may explain the difference in permeation profiles. The diffusivity of hydrogen in the deformed H900 sample is similar to that in undeformed H900 samples.