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Hydrogen can degrade the mechanical properties of steel components, which is commonly referred to as “hydrogen embrittlement” (HE). Quantifying the effect of HE on the structural integrity of components and structures remains challenging. The authors investigated an X70 pipeline steel through uncharged and hydrogen-charged (notched) tensile tests. This paper presents a combination of experimental results and numerical simulations using a micro-mechanics-inspired damage model. Four specimen geometries and three hydrogen concentrations (including uncharged) were targeted, which allowed for the construction of a fracture locus that depended on the stress triaxiality and hydrogen concentration. The multi-physical finite element model includes hydrogen diffusion and damage on the basis of the complete Gurson model. Hydrogen-Assisted degradation was implemented through an acceleration of the void nucleation process, as supported by experimental observations. The damage parameters were determined through inverse analysis, and the numerical results were in good agreement with the experimental data. The presented model couples micro-mechanical with macro-mechanical results and makes it possible to evaluate the damage evolution during hydrogen-charged mechanical tests. In particular, the well-known ductility loss due to hydrogen was captured well in the form of embrittlement indices for the different geometries and hydrogen concentrations. The limitations of the damage model regarding the stress state are discussed in this paper.

Damage in bearings is closely associated with the presence of microstructural alterations, known as white etching areas (WEAs) and white etching cracks (WECs). One of the main reasons for the creation of these microstructural alterations is the presence of defects in the material, such as non-metallic inclusions. Manganese sulfides and aluminum oxides are widely reported in the literature as the most common types of non-metallic inclusions found in bearing steels. This study classifies 280 non-metallic inclusions in an investigated bearing steel according to several criteria: bonded/debonded with the matrix, size, shape, orientation angle, depth below the raceway surface, and chemical composition. Contrary to the findings in the literature, this investigation reports that the chemical composition of the inclusion (MnS + Al2O3) is of secondary importance when considering factors for damage initiation. The orientation of the microstructural alterations is observed to coincide with the high-stress regions, indicating a relation between the formation of butterfly wings and the white etching crack. In our investigation, butterfly wings typically exhibit a 45-degree pattern originating from the non-metallic inclusions. Conversely, the white etching crack starts from the non-metallic inclusion at a shallower angle in correspondence to the raceway. This can be attributed to the stress state, which corresponds to a region where extensive white etching cracks are formed. In conclusion, the microstructural observations demonstrate that the state of non-metallic inclusion—i.e., whether they are bonded or not to the steel matrix—plays an essential role in initiating rolling contact fatigue damage.

The effect of cementite morphology on the corrosion layer formation of four high-strength carbon steels was studied in an aqueous solution containing CO2 and CO2/H2S. The linear polarization resistance and weight loss data reveal that as the cementite phase fraction is increased, the corrosion rate increases in CO2 environment, while no trend is observed in the CO2/H2S environment. The results indicate that a porous and, non protective corrosion layer forms in the CO2 environment, whereas a protective layer forms in the CO2/H2S environment. A mechanism that explains the role of cementite morphology on corrosion layer formation in a CO2 environment is proposed for the studied materials.

Low alloy steels combine relatively low cost with exceptional mechanical properties, making them commonplace in oil and gas equipment. However, their strength and hardness are restricted for sour environments to prevent different forms of hydrogen embrittlement. Materials used in sour services are regulated by the ISO 15156-2 standard, which imposes a maximum hardness of 250 HV (22 HRC) and allows up to 1.0 wt% Ni additions due to hydrogen embrittlement concerns. Low alloy steels that exceed the ISO 15156-2 limit have to be qualified for service, lowering their commercial appeal. As a result, high-performing, usually high-nickel, low alloy steels used successfully in other industries are rarely considered for sour service. In this work, the hydrogen stress cracking resistance of the high-nickel (3.41 wt%), quenched and tempered, nuclear-grade ASTM A508 Gr.4N low alloy steel was investigated using slow strain rate testing as a function of applied cathodic potential. Results showed that the yield strength and ultimate tensile strength were unaffected by hydrogen, even at a high negative potential of −2.00 VAg/AgCl. Hydrogen embrittlement effects were observed once the material started necking, manifested by a loss in ductility with increasing applied cathodic potentials. Indeed, A508 Gr.4N was less affected by hydrogen at high cathodic potentials than a low-strength (yield strength = 340 MPa) ferritic-pearlitic low alloy steel of similar nickel content. Additionally, hydrogen diffusivity was measured using the hydrogen permeation test. The calculated hydrogen diffusion coefficient of the ASTM A508 Gr.4N was two orders of magnitude smaller when compared to that of ferritic-pearlitic steels. Hydrogen embrittlement and diffusion results were linked to the microstructure features. The microstructure consisted of a bainitic/martensitic matrix with the presence of Cr23C6 carbides as well as Mo- and V-rich precipitates, which might have played a role in retarding hydrogen diffusion, kept responsible for the improved HE resistance.

Hypereutectoid martensitic steels possess excellent hardness levels which make them attractive materials for specific industrial applications. However, they can contain cracks and/or retained austenite after quenching which show a particular interaction with hydrogen (H). Hence, this work evaluates the interaction between H and a martensitic Fe-1.1C alloy by combining a wide variety of (H) characterization techniques with a systematic approach for specially designed H charged and heat treated samples. A detailed analysis of the microstructure for every condition serves as the basis for the interpretation. The results show that the presence of H leads to additional cracking and branching or growth of pre-existing quench cracks. Moreover, it is shown that when the temperature exceeds the retained austenite decomposition temperature while the austenitic grains contain H, additional cracking occurs which increases the amount of reversible H trapping sites thus raising the HE susceptibility.

This work evaluates the effect of hydrogen on the mechanical integrity of a weld in a martensitic base metal. Different regions in the heat-affected zone (HAZ) are reproduced to investigate the int...

Thermal desorption spectroscopy (TDS) was performed on ultra-low carbon (ULC) steel with various degrees of hydrogen-induced damage and deformation-induced defects. First, the extent to which hydro...

This work is part of a project that aims to develop a micromechanics based damage law taking into account hydrogen assisted degradation. A 'vintage' API 5L X56N and a 'modern' API 5L X70M pipeline steel have been selected for this purpose. The paper focuses on an experimental calibration of ductile damage properties of the well known complete Gurson model for the two steels in absence of hydrogen. A basic microstructural characterization is provided, showing a banded ferrite-pearlite microstructure for both steels. Charpy impact tests showed splits at the fracture surface for the X70 steel. Double-notched round bar tensile tests are performed, aiming to provide the appropriate input for damage model calibration. The double-notched nature of the specimens allows to examine the material state at maximum load in the unfailed notch, and the final material state in the failed notch. Different notch radii are used, capturing a broad range of positive stress triaxialities. The notches are optically monitored for transverse necking in two perpendicular directions (transverse to rolling and through thickness) to reveal any anisotropy in plastic deformation and/or damage. It is explained how the occurrence of splits at the segregation zone, and anisotropy complicate the calibration procedure. Calibration is done for each steel and acceptable results are obtained. However, the occurrence of splits did not allow to evaluate the damage model for the highest levels of tested stress triaxiality.

In the present study, the effect of Niobium (Nb) on the hydrogen embrittlement resistance of Quenched and Partitioning (Q&P) steel is investigated. For this purpose, the hydrogen uptake level and its impact on the mechanical properties of a Nb-free and a 0.024 wt% Nb Q&P steel are thoroughly analysed. The hydrogen trapping capacity is evaluated via thermal desorption spectroscopy (TDS). In-depth analysis of the desorption kinetics at different heating rates allows identification and quantification of the available trapping sites. The hydrogen embrittlement sensitivity of both steels is characterized using static and dynamic tensile tests. The addition of Nb results in an increase of the hydrogen concentration by more than 25%. The larger hydrogen content in the Nb steel, as a result of the higher fraction of grain boundaries/interphases, gives rise to a more severe embrittlement of the Nb steel compared to the Nb-free one. In addition to the larger hydrogen fraction in the Nb Q&P steel, the larger retained austenite fraction of low stability is detrimental due to the larger fraction of high carbon martensite formed when straining. This results in higher susceptibility to hydrogen embrittlement of the Nb microalloyed steel due to the brittle character of the high carbon martensite that forms easily during straining. Under dynamic loading conditions, the hydrogen embrittlement of both steels is minimal, which is attributed to a reduced hydrogen diffusion and the suppression of the transformation induced plasticity (TRIP) effect due to adiabatic heating.

This study presents hydrogen diffusion and trapping in the nickel Alloy 625 by employing the hot extraction test and the thermal desorption spectroscopy (TDS) analysis. Combined with electrochemical permeation test, the impact of grain size and grain boundary carbide on hydrogen diffusion are investigated. The results manifeste that the effective hydrogen diffusivity can be expressed as D = 1.03 x 10(-7) exp (-46.44kJ/mol/RT) m(2)/s for the sample with a grain size of similar to 8 mu m. The diffusion activation energy ED for hydrogen is determined as 42.05 -48.10 kJ/mol. The activation energy E associated with interstitial sites/elastic field of dislocations and reversible traps is 17.92-20.73 kJ/mol and 24.87-27.13 kJ/mol, respectively. Moreover, the reduction in grain size and the presence of grain boundary carbide can lower hydrogen diffusivity by locally changing the diffusion and trapping behavior of hydrogen. (C) 2022 The Author(s). Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.

The influence of the austenite (gamma) phase fraction on the hydrogen embrittlement of duplex stainless steel is investigated. Heat treatments are performed to create two duplex stainless steel specimens, containing 50% and 44% of austenite, respectively. Mechanical testing with and without hydrogen charging reveals that significant embrittlement occurs regardless of the austenite fraction. A higher austenite fraction results in a reduced ductility loss under the presence of hydrogen. Samples with a higher ferrite fraction are embrittled more due to their higher hydrogen diffusivity. In-situ tensile tests, interrupted at the ultimate tensile strength, show hydrogen-assisted cracks on the specimen surface both in austenite and ferrite and across the alpha/gamma interface.

This study evaluates the electrochemical hydrogen charging behavior and interaction between hydrogen and the microstructure of a duplex stainless steel. A saturation level of approximately 650 wppm is reached after 10 d of charging. The data are compared with a model resulting in a diffusion coefficient of 2.1 x 10(-14) m(2)/s. A two-step increase of the concentration is observed and ascribed to saturation of ferrite followed by charging of austenite grains. Microstructural changes are observed during charging, i.e., formation and interaction of dislocations, as a result of the high residual stresses inherent to the production process of duplex stainless steels.

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.

Notched TRIP tensile samples were strained until fracture and until the tensile strength under variable hydrogen charging conditions in order to assess the influence of hydrogen present in the samples (internal hydrogen) vs. hydrogen charged during tensile testing (environmental hydrogen) on the hydrogen assisted cracking behavior. Three types of charging conditions were applied: 1) pre-charging with hydrogen till saturation followed by tensile testing with in-situ electrochemical hydrogen charging during the test, 2) pre-charging with hydrogen till saturation and tensile testing without additional hydrogen charging during the test, and 3) tensile testing with in-situ electrochemical hydrogen charging, but without pre-charging. Environmental hydrogen was found to embrittle the material more than internal hydrogen, even though less hydrogen was present in the material. Fracture surface and secondary crack analyses indicated the importance of continuous hydrogen supply to critical zones during loading and the importance of the hydrogen/dislocation interaction in the failure process.

Hydrogen (H) induced mechanical degradation is studied in DP steel by performing tensile tests under static and dynamic conditions. Tensile specimens were electrochemically H charged and tensile tests were done ex-situ after charging. Different H contents were charged into the samples by modifying the current density. The strain rate is increased from static (1.67*10−2 and 1.67 s−1) to dynamic (450 and 900 s−1) conditions to verify the effect of H diffusivity during the tensile tests on the hydrogen embrittlement (HE) susceptibility. Therefore, a reproducible methodology was established by using a standardized tensile machine for static testing and split Hopkinson bar experiments for dynamic conditions. The HE degree increased with current density due to higher amount of H, as confirmed by melt extraction. The HE% also increased with slower strain rates since H was able to diffuse to a crack tip, hence accelerating failure. Even at the highest strain rate (900 s−1), the material lost about 10% of its ductility due to H present in the sample and not because of H diffusion during the test. This was concluded since H induced brittle failure initiated at the edges of the samples at slow strain rates. Though at a strain rate of 1.67 s−1, fracture initiated in a ductile way from the center similarly as for tests performed without charging. Fractographic visualization of the fracture surfaces revealed an embrittled central line when charged with H, which evolved into a major crack. MnS inclusions were found in this central line accounting for the H induced crack initiation.

Duplex stainless steels (DSS) have a microstructure of ferrite and austenite. These alloys have a high strength combined with ductility and good corrosion resistance. They are widely used in the petrochemical, paper and nuclear industries. However, like other stainless steels, they are susceptible to hydrogen embrittlement (HE). DSS 2205 samples were received under the condition of homogenization annealing (1050°C for 300 s and cooling in water). Then, they were cold rolled to 60% thickness reduction and annealed at 1100°C for 7200 s and aged at 850°C for 86400 s, then charged with hydrogen. Melt extraction analyzes were applied to quantify the hydrogen in the steel. In situ tensile tests, with simultaneous hydrogen charging, were used to assess the embrittlement caused by this element. Completing the hydrogen analyzes, thermal desorption spectra (TDS) were constructed. In the aged condition, the phases ferrite, austenite, sigma (σ), chi (χ) and carbide (M23C6 ) were identified. The DSS showed a considerable reduction in ductility, reaching 5% total elongation in the aged state. Hydrogen charging did not change this condition. Melt extraction revealed a hydrogen content in the microstructure of up to 50 wppm for the annealed condition, while for the aged sample it was 10 wppm.

Multiple types of hydrogen trapping sites in advanced high-strength steels (AHSS) are often experimentally characterized by means of thermal desorption spectroscopy (TDS). The evaluation is regularly based on the peak deconvolution procedure combined with Kissinger's theory, which provides distinctive desorption energies of hydrogen trapping sites at microstructural defects. However, the desorption energies published in literature are often non-conclusive and from time to time contradictive in nature. Therefore, it is of utmost importance to verify the evaluation procedures according to Kissinger's theory for multiple types of hydrogen trapping sites. For that purpose, theoretical TDS spectra were simulated using a bulk diffusion model according to Oriani's theory. Binding energies and trap densities were chosen for providing TDS spectra with clearly separated as well as overlapping TDS peaks. Finally, the desorption energies according to Kissinger's theory were compared with the theoretical trapping energies used in the models. Based on this theoretical work, it is strongly recommended to apply the Kissinger theory only for the evaluation of single or well separated TDS peaks. If peaks overlap, complementary microstructural variation and characterization are a perquisite to correctly evaluate the TDS spectra. (c) 2021 The Authors. Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. This is an open access article under the CC BY license (http://creativecommons.org/ licenses/by/4.0/).

Understanding the interaction of hydrogen with a steel microstructure is key toward further material development and a potential future hydrogen based economy. A reliable determination of the hydrogen diffusivity and trapping are crucial hereto. Electrochemical permeation is mainly used for the former, while thermal desorption spectroscopy (TDS) is opted for the latter. Combination of both, together with a detailed microstructural evaluation, provides fundamental insights for the engineering of suitable hydrogen traps and diffusion barriers. Finally, in-situ mechanical testing enables to evaluate the hydrogen embrittlement susceptibility and identifies the active deformation mechanism. This chapter summarizes some recent experimental advances and developments of our research group. At first, focus lies on the electrochemical permeation technique, which has been expanded to apply a constant load to the materials to evaluate the influence of stresses on hydrogen diffusivity during in-situ hydrogen permeation. Elastic load on dual-phase steel increases hydrogen diffusion due to crystal lattice expansion, while plastic deformation decreases diffusion due to the formation of lattice discontinuities, e.g., dislocations. Next, the ability to assess hydrogen trapping in austenite-containing materials is critically assessed for a duplex stainless steel, revealing that the TDS data are dominated by hydrogen diffusion in these low diffusivity materials. In-situ interrupted tensile testing on these materials is further complemented with scanning electron microscopy—electron backscatter diffraction analysis. \(\varepsilon \)- and \(\alpha \)’-martensite are found in austenite of the hydrogen-charged tensile specimens, while these martensitic transformation do not show in the uncharged samples. This is, among others, explained by a reduction in stacking fault energy due to the presence of hydrogen. Hydrogen-assisted cracks also initiate in these materials, mainly in the austenite phase. Finally, the hydrogen sensitivity is evaluated for high strength-low ductility Fe–C steels. Due to their brittle nature, a novel in-situ three-point bending setup is developed to evaluate their sensitivity to hydrogen. Hydrogen causes a transition from a microvoid (Fe–0.2C), intergranular (Fe–1.1C), or mixed (Fe–0.4C) fracture surface (air-tested samples), to a hydrogen-induced cleavage fracture appearance. This is accredited by the Hydrogen Enhanced Plasticity Mediated Decohesion mechanism, proposing that hydrogen is preferentially trapped at packet or block boundaries in high carbon steels, while lath martensitic boundaries play a minor role in the crack development.

Quenching and Partitioning (Q&P) steels are, due to their excellent combination of strength and ductility, seen as good candidates for the third generation advanced high strength steels (AHSS). Although the TRIP effect is beneficial for the overall mechanical behaviour of these steels it potentially can have detrimental effects when strained in a hydrogenenriched environment. The solubility of hydrogen is high in austenite but low in high carbon martensite. Martensite is even in the absence of hydrogen already a possible damage initiation spot. The effect of hydrogen under static and dynamic tensile loading was evaluated in a Q&P and a Nb micro-alloyed Q&P steel. Experiments were carried out under a strain rate ranging from 0.03 s-1 till 500 s-1 and correlated with the hydrogen uptake characterised via thermal desorption spectroscopy (TDS). The presence of Nb resulted in a 25% increase in the hydrogen uptake capacity. A higher susceptibility to hydrogen was observed in the Nb steel partially due to the high hydrogen fraction, but also because of the larger fraction of low stability austenite. However, when tested under dynamic conditions the hydrogen susceptibility is minor and even improved in the micro-alloyed Q&P steel compared to the standard Q&P steel.

This work evaluates the effect of film-forming amines (FFA) on the acidic stress-corrosion cracking (SCC) resistance of NiCrMoV turbine steel. Contact angle measurements show an increased hydrophobicity of the surface when coating the steel with oleyl propylene diamine (OLDA). According to potentiodynamic measurements and post-mortem scanning electron microscopy (SEM) analysis, anodic dissolution and hydrogen embrittlement still occur when the steel is FFA coated. In situ constant extension rate testing (CERT) in acidic aqueous environment at elevated temperature of FFA-coated steel shows a ductility gain compared to non-coated steel, explained by a decrease in both corrosion rate and hydrogen uptake.

The present study evaluates thermal desorption spectroscopy (TDS) data measured for UNS S32205 duplex stainless steel. Variations in the TDS spectra are obtained by electrochemical hydrogen charging for different times and by applying different heating rates for desorption to evaluate the desorption activation energy. Good agreement is found when comparing the experimental TDS curves with the desorption flux based on a numerical diffusion model using a homogeneous average hydrogen diffusion coefficient for the two-phase (ferrite-austenite) duplex microstructure. Trapping cannot be distinguished from the experimental TDS data since hydrogen diffusion in austenite is the rate-determining process during desorption. An average diffusion activation energy of 43.4 kJ/mol is determined from the experiments. Moreover, similar findings are obtained with a finite-element model that includes the heterogeneous hydrogen-related properties of the two phases of this duplex stainless steel.

The goal of this work is to propose a general mechanism for hydrogen induced crack initiation in steels based on a microstructural study of multiple steel grades. Four types of steels with strongly varying microstructures are studied for this purpose, i.e. ultra low carbon (ULC) steel, TRIP (transformation induced plasticity) steel, Fe-C-Ti generic alloy, and pressure vessel steel. A strong dependency of the initiation of hydrogen induced cracks on the microstructural features in the materials is observed. By use of SEM-EBSD characterization, initiation is found to always occur at the hard secondary phase particles in the materials.

The hydrogen induced damage of generic Fe-C-Ti and Fe-C-V ferritic alloys was investigated to assess the influence of precipitates on the hydrogen sensitivity of a material. The precipitates, formed during heat treatment, were evaluated by scanning transmission electron microscopy (STEM). The hydrogen/material interaction was evaluated by: 1) melt and hot extraction to determine the total and diffusible hydrogen content, respectively, 2) permeation experiments to calculate the diffusion coefficient, 3) thermal desorption spectroscopy to determine the hydrogen trapping characteristics of the materials. Furthermore, two different types of hydrogen induced damage were evaluated, i.e. hydrogen assisted cracking and blistering, resulting from electrochemical hydrogen charging with and without the application of an external load, respectively. Evaluation of the hydrogen induced damage and the role of the precipitates was performed by combining optical microscopy, scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). An important though divertive role of diffusible hydrogen is observed in both damage mechanisms for the investigated microstructures. On the one hand, a large amount of diffusible hydrogen compared to strongly trapped hydrogen promotes hydrogen assisted cracking of materials, while on the other hand, the blistering phenomenon is delayed under such conditions.

A new thermal desorption spectroscopy (TDS) apparatus was used to identify the hydrogen trapping peaks, and to measure the hydrogen concentrations in 3.5NiCrMoV steel after hydrogen charging electrochemically, and in gaseous hydrogen. The hydrogen concentration increased with (i) increasingly negative charging potential and (ii) increasing hydrogen gas pressure. The equivalent hydrogen fugacity versus charging overpotential was derived. There was a difference in the diffusible hydrogen traps activated during electrochemical and gas phase charging, attributed to the difference in the hydrogen fugacity. A two-site model for Sieverts' Law explained the positive Y-intercept, as the density of already filled hydrogen traps.

The hydrogen trapping efficiency of different types of W based precipitates is considered in three generic Fe C W alloys with increasing carbon content and a stoichiometric amount of W. A martensitic microstructure is prepared and two conditions are compared; i.e. an as-quenched (as-Q) state and a quenched and tempered (Q&T) state in which W based carbides are formed. The tempering time and temperature are modified to change the carbide characteristics. Hence, the hydrogen trapping characteristics are evaluated for the different carbides. Melt extraction is done to determine the hydrogen content, whereas thermal desorption spectroscopy (TDS) is performed to verify whether the tempered induced carbides are able to trap hydrogen efficiently. The trapping capacity is found not only to be size dependent, but also reliant on the morphology and type of the carbides, as investigated by transmission electron microscopy. TDS revealed that the tempered induced W2C in the Q&T at 600 °C for 1 h condition do not trap hydrogen due to their rather large size (>20 nm) and hence incoherent nature. Moreover, the hydrogen content is decreased compared to the as-Q condition due to the reduced dislocation density. The tempering time is reduced to 10 min to evaluate the size effect on the carbide trapping ability. As such, smaller W2C (

The present work considers the effect of hydrogen on the mechanical properties of generic Fe-C-W alloys. Thermal treatment aimed at a martensitic microstructure and two conditions are compared; i.e. an as-quenched state and a quenched and tempered state with lower dislocation density and with W based carbides formed during tempering. The hydrogen induced mechanical degradation is evaluated by in-situ tensile tests, while thermal desorption spectroscopy, hot/melt extraction and permeation experiments are performed to understand the observed hydrogen embrittlement degree. The hydrogen induced ductility loss increases with increasing carbon content due to the higher amount of hydrogen trapped by the denser martensitic lath boundaries. Furthermore, the quenched and tempered condition shows a lower susceptibility to hydrogen. This is correlated to the reduced hydrogen content when tempered due to a decreased dislocation density and the fact that the tempered induced W2C particles did not trap hydrogen. Moreover, corresponding observations to this interpretation are perceived by permeation experiments since, on the one hand, the diffusion coefficient decreases with carbon content due to the increasing trapping ability of alloy A ➔ B ➔ C, and, on the other hand, the diffusivity increases when tempering is applied, which is also linked to the decrease in dislocation density and the disability of the carbides to hinder hydrogen diffusion by efficient trapping.

The hydrogen trapping ability of 15 Fe-C-X alloys is compared in this work. Five types of carbides, i.e. Ti, Cr, Mo, W and V based carbides, and their effect on the hydrogen embrittlement susceptibility is considered while three carbon contents are prepared for each carbide former. Two conditions are compared for each alloy to evaluate the hydrogen/material interaction: an as quenched and quenched and tempered condition in which carbides are introduced. Next to the material characterization, also the interaction of hydrogen with the materials is completely elaborated. At first, in-situ tensile tests are done to determine the hydrogen induced ductility loss. To interpret the obtained degrees of hydrogen embrittlement, hot/melt extraction is done to determine the hydrogen content, whereas thermal desorption spectroscopy is performed to assess the hydrogen trapping capacity of the tempered induced precipitates and the different other potentially hydrogen trapping microstructural features. These measurements are done after hydrogen pre-charging till saturation. The tempered induced TiC and V4C3 are capable of trapping a significant amount of hydrogen, while the Mo2C and Cr23C6 particles only trap a limited amount of hydrogen. The W2C precipitates, however, are not able to trap hydrogen. The size and coherency of the carbides are considered to be the main factor determining their trapping ability. The degree of hydrogen embrittlement is correlated with the hydrogen present in the alloys. Three amounts of hydrogen were determined by the strength by which they were trapped by combining the different hydrogen characterization techniques, i.e. total, diffusible and mobile hydrogen. It was confirmed that hydrogen trapped by dislocations plays a determinant role. This further confirms the importance of an enhanced dislocation mobility in the presence of hydrogen, as described in the HELP mechanism.

Hydrogen characterization techniques like melt extraction and thermal desorption spectroscopy (TDS) are useful tools in order to evaluate and understand the interaction between hydrogen and metals. These two techniques are used here on cold deformed ultra-low carbon (ULC) steel with and without hydrogen induced damage. The material is charged electrochemically in order to induce varying amounts of hydrogen and variable degrees of hydrogen induced damage. The aim of this work is to evaluate to which extent the hydrogen induced damage would manifest itself in melt extraction and TDS measurements.

Hydrogen (H) presence in metals is detrimental as unpredictable failure might occur. Recent developments in material’s design indicated that microstructural features such as precipitates play an essential role in potentially increasing the resistance against H induced failure. This work evaluates the H trapping characteristics for TiC and V4C3 by thermal desorption spectroscopy and permeation experiments. Two microstructural conditions are compared: as quenched vs. quenched and tempered, in which the carbides are introduced. The tempered induced precipitates are able to deeply trap a significant amount of H, which decreases the H diffusivity in the materials and removes some of the detrimental H from the microstructure. For microstructural design purposes, it is important to know the position of H. Here, H is demonstrated to be trapped at the carbide/matrix interface by modifying the tempering treatment.