Hydrogen embrittlement leads to mechanical degradation of metals. Hence, hydrogen sorption/desorption properties of metals need to be characterized. An electrochemical procedure based on cyclic voltammetry (CV) and potentiostatic polarization is elaborated on plain-carbon steel. The procedure consists of first two consecutive CV cycles (pretreatment and reference CV), followed by cathodic H-charging, and subsequent CV scans to study and quantify the H-sorption/desorption. Best practice in this procedure is to perform all steps consecutively without interruption or sample manipulations between steps to avoid spontaneous H-loss. The H-related interaction with the steel is clearly identified in the CV and can be differentiated from the electrolyte contribution coming from thiourea. The study confirms the role of thiourea as H-recombination poison in alkaline solution, and also demonstrates that it contributes to the CV response. Additionally, various charging times are investigated to study the time to H-saturation, and also the scan rate during the CV procedure is varied to study time-related phenomena. Dedicated discharging experiments were included in the study to complement the CV data, giving additional insights in the H-steel interaction. Moreover, hydrogen related findings are successfully verified by using a complimentary method, i.e. hot extraction. The better understanding of the peaks in the CV and the continuous procedure result in a reliable methodology to characterize the H-sorption/desorption in steel. Hydrogen embrittlement is the phenomenon leading to mechanical degradation of metals, in particular, a loss of ductility and toughness. The intensity of hydrogen degradation depends on many factors related to the nature of hydrogen and the material itself. Hydrogen can be incorporated in steel during the manufacturing process as well as during various stages of its use. After hydrogen absorption, it diffuses into the microstructure and is distributed between interstitial sites in the metal lattice and its structural defects. The hydrogen in the microstructure can roughly be classified in two forms, diffusible and trapped hydrogen.1 Although the term diffusible hydrogen has multiple descriptions in literature, it can be considered as the hydrogen that can move between lattice positions within a reasonable time frame according to the laws of diffusion. On the other hand, hydrogen that resides for a longer time near microstructural inhomogeneities (interfaces, grain boundaries, precipitates) as well as hydrogen accumulated in micro cracks and blisters, is called trapped.2 Depending on the binding energy of hydrogen to the trapping sites, trapped hydrogen can be classified as reversible or irreversible. [3][4][5][6] To study the hydrogen-trap interaction, thermal desorption spectroscopy (TDS) can be used. By means of this method, an activation energy of the traps can be determined and the traps can be categorized as reversible or irreversible, as studied in e.g. Refs. 7-15. For instance, MnS inclusions wit...

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Using a light optical microscope (LOM), microstructural analysis is carried out on plain-carbon, DP600, and As-Quenched (As-Q) martensitic steels to identify the different phases interacting with hydrogen. Our recently developed electrochemical procedure, based on cyclic voltammetry (CV) and potentiostatic discharging method, is applied on these steel alloys having different phases to monitor H-uptake in the steels with respect to their microstructural features. The electrochemical method is capable of measuring diffusible Hconcentration (including mobile hydrogen) for the steel alloys under H-charging condition, where hydrogen embrittlement phenomena can occur within in-service environments. The best practice in this procedure is to perform electrochemical H-measurements immediately after H-charging without interruption between steps to avoid spontaneous H-loss. Various charging times are investigated to estimate the time to near H-saturation for each steel alloy. To gain additional insights in our H-related findings, hot extraction measurements are performed to measure the diffusible H-concentration in the steels. A clear correlation between the results of hot extraction and electrochemical discharging methods is confirmed by a mathematical model, based on Fick's Law, predicting diffusible H-loss due to the time lag. Thus, under the used charging conditions, As-Q martensitic steel has been found to contain the lowest amount of diffusible hydrogen, with its near H-saturation reached after 4 hours of H-charging. DP600 is H-saturated after one hour of charging, while near H-saturation for plain-carbon steel is attained after 30 minutes. The fraction of mobile-H in plain-carbon steel is relatively higher than in DP600 steel.