The presence of hydrogen in metals is known to be detrimental for the overall performance and more specific the ductility of the materials. Well-designed hydrogen trapping sites might offer a relevant strategy to enhance the resistance to hydrogen embrittlement. The present work considers four types of carbides (Ti, Cr, Mo and V-based carbides) in Fe-C-X alloys with three different carbon contents, together with pure iron and dual phase steel as a reference. Two conditions were compared for each Fe-C-X alloy to evaluate the effect of these precipitates: as quenched and quenched and tempered, where in the latter carbides were introduced. In-situ tensile tests, thermal desorption spectroscopy, hot/melt extraction and permeation experiments were performed after hydrogen pre-charging till saturation without hydrogen induced damage.
Hydrogen trapped by the precipitates did not have a considerable impact of the hydrogen induced mechanical degradation. For all carbides, the addition was beneficial to enhance the resistance since they were able to deeply trap a significant amount of hydrogen. The degree of hydrogen embrittlement was correlated with the amount of hydrogen present in the alloys. Three different kinds of hydrogen, related to the strength by which they were trapped, were determined by combining the different hydrogen characterization techniques. It was assumed that hydrogen trapped at dislocations played a determinant role. To confirm this hypothesis, different degrees of cold deformation were applied on the Fe-C-X alloys, pure iron and dual phase steel. Hence, the dislocation density increased which was clearly visualized by the TDS spectra as the first peak increased considerably. Finally, in-situ tensile tests on these materials confirmed an increased sensitivity to hydrogen embrittlement when more prior cold deformation was applied. This further set the importance of an enhanced dislocation mobility in the presence of hydrogen, which is a solid experimental proof of the HELP mechanism.