Experimental study of the hydrogen-microstructure interactions in a pre-strained 316L austenitic stainless steel

The present study aims at investigating the interactions between hydrogen and deformation-induced defects in a 316L austenitic stainless steel (SS). The studied material was pre-strained up to different levels. The resulting microstructures were characterized by optical and electron microscopy and by X-ray diffraction. Dislocation densities were systematically quantified showing a more than 50-fold increase between the unstrained and the most pre-strained sample. Cathodic charging was employed to introduce deuterium into the material. By means of Thermal Desorption Spectrometry (TDS) and Secondary Ions Mass Spectrometry (SIMS) analyses, deuterium energetic and spatial distributions were evaluated both just after charging and after an additional isothermal aging treatment. Thanks to aging treatments, three different energetic states of deuterium in the 316L SS were evidenced: interstitial 2H, low-energy trapped 2H and high-energy trapped 2H. Probing the low-energy trapping was challenging – probably due to the proximity between the migration enthalpy and the associated detrapping energy – but aging highlighted it. This low-energy contribution, displayed in TDS results, increased with the pre-strain level and the dislocation density, and was associated with dislocations elastic fields. Contrary to our expectations, the high-energy trapping could not be correlated directly neither to the pre-strain level nor to the dislocation density. Trapping at vacancies was suggested. •Aging after hydrogen charging evidenced two types of strain-induced trap sites.•The low-energy trapping was attributed to the elastic fields of the dislocations.•The amount of hydrogen in this energy state increased with the pre-strain level.•The high-energy trapping was assigned to the dislocations cores or vacancies.