MARTENSITIC-TRANSFORMATION IN CATHODICALLY HYDROGEN CHARGED TYPE-316 AUSTENITIC STAINLESS-STEELS

Cathodically hydrogen charged type 316 austenitic stainless steel has been studied by x-ray diffraction. Both epsilon and alpha' martensites are formed by cathodic charging in solution-treated samples, however very small amount of additional martensitic phase formation was observ ed in cold-worked samples. The volume fraction of epsilon phase decrea ses with increasing ageing time. Epsilon and alpha' phases revert to g amma phase below 723 K and 923 K, respectively. The incorporated hydro gen induces the metastable epsilon and alpha' phases. The transformati on is suppressed by the tangled dislocation networks introduced by col d work. epsilon phase is more unstable, thereby it converts to alpha' and gamma phases by hydrogen release. The hydrogen concentration in - phase is higher han that in gamma phase and that in alpha' phase is ve ry low. The change of the x-ray profiles during ageing comes from the change of the spatial distribution of hydrogen atoms. By fitting the o bserved profiles to those calculated by Fick's law, the diffusion coef ficent of hydrogen has been evaluated as 1.0 X 10(-11) cm2 s-1, for bo th epsilon and gamma phases.