Martensitic Transformation in Cathodically Hydrogen Charged Type 316 Austenitic Stainless Steels

Abstract

Cathodically hydrogen charged type 316 austenitic stainless steel has been studied by x-ray diffraction. Both ε and α’ martensites are formed by cathodic charging in solution-treated samples, however very small amount of additional martensitic phase formation was observed in cold-worked samples. The volume fraction of ε phase decreases with increasing ageing time. ε and α’ phases revert to y phase below 723 K and 923 K, respectively. The incorporated hydrogen induces the metastable ε and α’ phases. The transformation is suppressed by the tangled dislocation networks introduced by cold work. ε phase is more unstable, thereby it converts to α’ and y phases by hydrogen release. The hydrogen concentration in ε phase is higher han that in y phase and that in α’ phase is very low. The change of the x-ray profiles during ageing comes from the change of the spatial distribution of hydrogen atoms. By fitting the observed profiles to those calculated by Fick’s law, the diffusion coefficent of hydrogen has been evaluated as 1.0x10-11 cm2s-1, for both ε and y phases. © 1993, The Japan Academy. All rights reserved.