Abstract
Hydrogen permeation in AL 29-4-2 ferritic and AISI 301 austenitic stainless steels was studied using an electrochemical method. Hydrogen was charged increasingly or decreasingly in steps and the effective hydrogen diffusivities were obtained from the build-up and decay transients. For AL 29-4-2 with Pd-coating on the exit side, except for the first build-up transient, the subsequent build-up and the conjugate decay transients yielded the same diffusivity data. For AISA 301, consistent diffusivities including the first build-up transient were obtained. Cyclic cathodic polarization demonstrated that the entry surface was cleaned out under a small cathodic charging current for both alloys. In addition, by comparing the effective diffusivities for Pd-coated (on the exit surface) and uncoated AL 29-4-2 with various thicknesses, it was found that the diffusivity dependend only on hydrogen concentration in the specimen, but not on the surface treatment. Therefore, under proper experimental conditions, surface impedance on both entry and exit sides could be neglected for these steels. © 1991.