Assessment of the potential of hydrogen plasma charging as compared to conventional electrochemical hydrogen charging on dual phase steel

The present study evaluates the hydrogen induced damage by in-situ hydrogen plasma charging in dual phase (DP) steel. Cold deformation of 15% is applied on the material to change microstructural defects, such as dislocation density. The susceptibility to hydrogen embrittlement is hence evaluated for two material conditions, i.e. DP 0% and DP 15%. Small scale tensile tests are done inside an ESEM chamber for which in-situ hydrogen plasma charging is compared with electrochemical hydrogen charging while uncharged samples serve as a reference. Generally, the hydrogen effect on the ductility and stress level is increased when deformation is applied, due to the hydrogen trapping ability of the deformation induced defects, as confirmed by thermal desorption spectroscopy. Complementary in-situ electrochemical nanoindentation tests verify the more pronounced hardness increase due to hydrogen when cold deformation is applied. A slightly increased ductility loss is observed when the samples are charged electrochemically, although similar tendencies are found for both hydrogen charging procedures. These observations are confirmed by the fractographic analysis, where the detrimental role of MnS inclusions in the segregation line on hydrogen induced cracking is demonstrated as well.