Hydrogen diffusivity measurement and microstructural characterization of Custom 465 stainless steel

Hydrogen diffusivity in Custom 465 (R) martensitic precipitation hardened stainless steel is determined using electrochemical permeation tests. Hydrogen diffusivity in the solution annealed (SA) condition is approximately 10 times higher than in the aged H900 (480 degrees C, 4 h) condition because of hydrogen traps such as Ni3Ti nano-precipitates and reverted austenite. The microstructure of the alloy is characterized by TEM, XRD and ESEM/EBSD, both in the aged H900 and in the SA conditions. In the aged condition, eta-Ni3Ti nano-precipitates with hexagonal structure and a rod-like shape are observed. In addition, reverted austenite is found at grain boundaries and inter-lath interfaces. In the SA condition, these microstructural features are not evident, which may explain the higher diffusivity measured. The diffusivity is almost unaffected by prior microplastic deformation of H900. (C) 2015 Elsevier Ltd. All rights reserved.