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In this work, hydrogen diffusion behavior and mechanisms in the 4130X steel influenced by temperature, locally high concentration, and grain boundary were studied by leveraging both electrochemical hydrogen permeation experiments and molecular dynamics simulations. It was revealed that the hydrogen diffusion coefficient of the 4130X steel was increased with increasing temperature and decreasing locally high hydrogen concentration. The grain boundaries with misorientation below 15° characterized by an electron backscatter diffraction map were identified as hydrogen trapping sites, thus rendering a lower mean square displacement of hydrogen atoms and localized hydrogen diffusion trajectories. Furthermore, at a high hydrogen concentration of 4 at. %, these grain boundaries were saturated by hydrogen atoms, and platelet-like hydrogen clusters were formed within the lattice, which further inhibited the diffusive motion of hydrogen atoms. These findings would deepen our understanding of hydrogen embrittlement mechanisms by establishing the connections between macroscopic permeation behavior and atomic-scale hydrogen diffusion in structural materials. [ABSTRACT FROM AUTHOR]

Uranium-based materials are valuable assets in the energy, medical, and military industries. However, understanding their sensitivity to hydrogen embrittlement is particularly challenging due to the toxicity of uranium and the computationally expensive nature of quantum-based methods generally required to study such processes. In this regard, we have developed a Chebyshev Interaction Model for Efficient Simulation (ChIMES) that can be employed to compute energies and forces of U and UH3 bulk structures with vacancies and hydrogen interstitials with accuracy similar to that of Density Functional Theory (DFT) while yielding linear scaling and orders of magnitude improvement in computational efficiency. We show that the bulk structural parameters, uranium and hydrogen vacancy formation energies, and diffusion barriers predicted by the ChIMES potential are in strong agreement with the reference DFT data. We then use ChIMES to conduct molecular dynamics simulations of the temperature-dependent diffusion of a hydrogen interstitial and determine the corresponding diffusion activation energy. Our model has particular significance in studies of actinides and other high-Z materials, where there is a strong need for computationally efficient methods to bridge length and time scales between experiments and quantum theory. [ABSTRACT FROM AUTHOR]

The increasing demand for energy and the urgent need to reduce carbon emissions have positioned hydrogen as a promising alternative. This review paper explores the potential of hydrogen blending in natural gas pipelines, focusing on the compatibility of pipeline materials and the associated safety challenges. Hydrogen blending can significantly reduce carbon emissions from homes and industries, as demonstrated by various projects in Canada and globally. However, the introduction of hydrogen into natural gas pipelines poses risks such as hydrogen-assisted materials degradation, which can compromise the integrity of pipeline materials. This study reviews the effects of hydrogen on the mechanical properties of both vintage and modern pipeline steels, cast iron, copper, aluminum, stainless steel, as well as plastics, elastomers, and odorants that compose an active natural gas pipeline network. The review highlights the need for updated codes and standards to ensure safe operation and discusses the implications of hydrogen on material selection, design, and safety considerations. Overall, this manuscript aims to provide a comprehensive resource on the current state of pipeline materials in the context of hydrogen blending, emphasizing the importance of further research to address the gaps in current knowledge and to develop robust guidelines for the integration of hydrogen into existing natural gas infrastructure. • Hydrogen blending in natural gas pipelines can significantly reduce carbon emissions. • Hydrogen embrittlement poses safety risks for pipeline materials in NG infrastructure. • Testing shows minimal yield strength changes after hydrogen exposure in various steels. • Fracture toughness of pipeline steels decreases notably with increasing hydrogen pressure. • Advanced testing and materials development are needed for safe hydrogen integration. [ABSTRACT FROM AUTHOR]

The occurrence of hydrogen embrittlement often leads to significant fracturing in materials. Thus, a comprehensive understanding of the interactions of hydrogen and its effects on material properties is essential. In this study, first‐principle calculations based on density functional theory are conducted to investigate the adsorption and diffusion characteristics of hydrogen at the Ni/Ni3Al(γ/γ') interface of a Ni‐based single‐crystal superalloy. The results show that hydrogen can stably adsorb onto the γ/γ′ interface, nearby octahedral interstitial sites, and tetrahedral interstitial sites in the γ‐phase. Analysis of the density of states and charge density confirms that the hydrogen atoms formed covalent bonds and ionic bonds with nearby Al atoms. A transition state structure search based on linear synchronous transit (LST) and quadratic synchronous transit (QST) models is utilized to calculate the diffusion paths and energy barriers of the hydrogen atoms between the stable adsorption sites near the interface. In addition, the permeation characteristics of hydrogen atoms at the interface are analyzed. Furthermore, it is confirmed that hydrogen atoms entering the matrix from the interface preferentially occupy the positions of the regular octahedral interstitial sites, diffuse towards adjacent regular 6Ni octahedral interstitial sites through the inclined octahedral interstitial sites between the atomic layers, and converge at the interface. [ABSTRACT FROM AUTHOR]

The phenomenon of hydrogen trapping in precipitates of steels is well-recognized, though a precise atomic level understanding remain elusive, leading to ongoing debates. This study highlights the specific roles of interfaces under various coherent conditions through first-principle calculations, incorporating local stress level, which is a novel aspect seldom explored in previous studies. It was found that coherent interfaces exhibit varying hydrogen-trapping capacities depending on their defect states, with the lowest hydrogen solution energy reaching −0.83 eV, primarily functioning as reversible traps. In contrast, derivative interfaces demonstrate superior hydrogen-trapping capacity, with hydrogen solution energy reaching −1.28 eV, classifying them as irreversible sites. Specific tensile or compressive stresses do not necessarily enhance the entrapment or release of hydrogen at precipitate interfaces; instead this depends on the characteristics of polyhedral interstices within the interfaces, with residual stress from hydrogen segregation also playing a critical role. These findings help address certain apparent controversies and advance understanding of the hydrogen embrittlement mechanism. Comprehensive investigation of H trapping characteristics of precipitates with various coherent conditions under stress. [Display omitted] • Perfect coherent precipitates exhibit very limited H-trapping capacity. • Coherent interfaces with Es reaching −0.83 eV mainly serve as reversible traps. • Derivative interfaces with Es reaching −1.28 eV function as irreversible traps. • Various stress levels can enhance H entrapment or release at precipitate interfaces. [ABSTRACT FROM AUTHOR]

Toughness characteristics of four hydrogen-charged austenitic stainless steels (ASSs) with 5–10 wt% Mn replacing Ni were investigated. The steels were subjected to long-term high-pressure hydrogen (H)- charging followed by Charpy impact tests from ambient to cryogenic temperatures. Various TRIP or TWIP rates were examined based on austenite stability and test temperature, and microscopic fracture mechanisms were observed to understand how they influenced microcracking at the notch tip area. The results indicated that 9%Ni–5%Mn ASS showed minimally reduced Charpy energy from H-charging due to abundant twins and suppression of martensitic transformation, whereas 6%Ni–10%Mn ASS exhibited significantly lower absorbed energy and HE resistance due to abundant martensite and δ-ferrite formed by its low stacking fault energy. Degradation by H increased with Ni/Mn replacement due to a decrease in activation energy for H diffusion, which resulted in pronounced H-enhanced decohesion, further decreasing Charpy impact energy after gaseous H-charging in Ni/Mn replaced ASSs. [Display omitted] • Charpy impact energy was analyzed in relation to hydrogen and Ni/Mn replacement. • Long-term high-pressure H-charging was applied for austenitic Charpy specimens. • Applied instrumented Charpy concept to interpret dynamic fracture mechanisms. [ABSTRACT FROM AUTHOR]

Hydrogen embrittlement (HE) extant a substantial concern to press-hardened steel (PHS) owing to superior strength. The high strength to light-weight automobile structures necessitates the advancement of superior HE resistance PHS. This study investigated the HE susceptibility of Nb-microalloyed PHS by slow strain rate tensile testing, u-shaped constant bending load test, and thermal desorption spectroscopy. Nb enhances microstructure and HE resistance by introducing retained austenite, refining prior austenite grains (21.14–13.73 μm), forming low-angle grain boundaries, and nano-scale precipitates. Nb-alloyed steel exhibits no-cracking over 300 h under high pre-bending stress and decreases elongation loss up to 48% in hydrogen environment as compared to Nb-free steel. Diffusible H-content in 0.12 wt% Nb-steel reduces to 14.9% of that in Nb-free steel owing to enhanced hydrogen traps, the Fcc/Bcc matrix, and carbide precipitation. The multi-phase microstructure with nano-scale NbC precipitation impeded the localized H-dispersion, enhancing the HE resistance in PHS despite its high strength. [Display omitted] • Grain boundary strengthening achieved by refined microstructure in Nb-steel. • Retained austenite with NbC enhances hydrogen embrittlement resistance. • 0.12 wt% Nb steel mitigate diffusible hydrogen content to 14.9% of that Nb-free steel. • Nb-alloying decreases elongation loss by up to 48% in presence of hydrogen. [ABSTRACT FROM AUTHOR]

The effect of co-existence of Mo and B on hydrogen embrittlement (HE) of equiatomic CoCrFeNi and (CoCrFeNi) 96.96 Mo 3 B 0.04 (MoB-doped) alloys are investigated through electrochemical hydrogen charging, tensile tests and advanced microstructural characterization. The MoB-doped alloy exhibits higher HE resistance than CoCrFeNi alloy, which is attributed to MoB-promoted twinning deformation process instead of conventionally strengthening grain boundary (GB) effect resulting from Mo and B segregation. As hydrogen charging time increases, the ductility of both alloys first increases and then decreases, which correlates with the competition relation between H-promoted formation of gradient twins/stacking faults and hydrogen-enhanced decohesion mechanism. For the samples charged 3 h, the beneficial effect of gradient nanostructure caused by chemical composition gradients of hydrogen overcompensates its HE effect, leading to the defeating HE of the alloys by hydrogen itself. This result indicates that the introduction of gradient nanostructures through hydrogen-concentration gradients could be a way forward for designing hydrogen-tolerant alloys. [Display omitted] • Hydrogen can enhance the ductility of CoCrFeNi and MoB-doped alloys. • Hydrogen promotes the formation of twins and stacking faults. • Segregation of Mo and B along grain boundaries are not observed. • MoB-promoted twin deformation process favors high HE-resistance of the alloy. [ABSTRACT FROM AUTHOR]

The hydrogen embrittlement behavior of Ni–Cr–Mo-based superalloy fabricated by wire arc additive manufacturing (WAAM) with or without solution treatment was investigated by electrochemical hydrogen charging. The results show that the dissolution of the Laves phase promotes the precipitation of the δ phase in the matrix of WAAM superalloy after solution treatment at 980 °C. When the solution temperature goes up to 1080 °C, the large Laves phase disappears and only MC exists in the matrix. The interfaces between the Laves phase/δ phase and matrix generally could act as hydrogen traps, which would reduce the motion of hydrogen and lead to high hydrogen embrittlement resistance of the WAAM and ST-980 °C samples. However, hydrogen mainly accumulates on grain boundaries in the ST-1080 °C due to the disappearance of the Laves phase and δ phase. Hydrogen-induced intergranular brittle fracture occurs during the slow strain rate tensile test and the ST-1080 °C samples exhibit higher hydrogen embrittlement susceptibility than that of the WAAM and ST-980 °C samples. • The solid solution changes the element distribution and precipitates in the WAAM superalloy. • The effect of hydrogen on the mechanical properties of the WAAM superalloy was investigated. • The hydrogen diffusion in the WAAM superalloy is affected by dendrite, Laves phase and δ phase. • The fracture mode of the hydrogen-containing WAAM superalloy is different under different solid solution temperatures. [ABSTRACT FROM AUTHOR]

The location of the H atoms in Ti, Zr, and Hf is crucial to the formation of the hydrides in these metals as it influences the crystal lattice transformation and the hydrogen diffusion involved in the hydride formation process. Although Ti, Zr, and Hf are all of hexagonal close-packed structure with similar lattice parameters, the solute H atom occupies the octahedral interstice in Ti but the tetragonal interstice in Zr and Hf, of which the origin is still mysterious. In the present work, the origin of the distinct site occupation behavior of H atom in Ti and Zr/Hf is investigated through first principles calculations. The calculated solution energies confirm that H prefers the octahedral interstice in Ti but the tetrahedral interstice in Zr and Hf. We ascribe the distinct site occupations of H in Ti and Zr/Hf to the varying Coulomb repulsion between the H (as a screened proton in the metals) and the matrix atoms against the interstitial size. The competition between the H-induced electron accumulation effect and the matrix atom debonding effect might matter as well. We propose that, as a general rule, a H atom prefers the site with a trade-off between a large space and a high electron density in metals. • Hydrogen occupies octahedral interstice in Ti but tetrahedral interstice in Zr/Hf. • H-metal atom Coulomb repulsion is responsible for the distinct site occupation of H. • H-induced electron redistribution might matter to the distinct site occupation of H. • H prefers the site with a trade-off between large space and high electron density. [ABSTRACT FROM AUTHOR]

Understanding the trapping and diffusion mechanism of hydrogen in vanadium carbide (VC) precipitates is crucial for exploring the issue of hydrogen embrittlement in steel. Although there is widespread consensus that VC can trap hydrogen, the mechanism by which hydrogen diffuses into VC is still unclear. In this study, we used first-principles calculation methods to study the influence of different spacings of carbon vacancies on the trapping and diffusion of hydrogen in VC. The increase in the number of C vacancies makes it easier for vacancies to trap hydrogen, and hydrogen tend to fill up C vacancies. The diffusion of hydrogen into VC only occurs via neighboring C vacancies at a distance of 0.295 nm (connecting vacancies), leading to a diffusion barrier of 0.63–0.78 eV. This is consistent with experimental results and validates the experimental speculation that the diffusion of hydrogen in VC requires a connecting C vacancy grid. [Display omitted] • Connectivity of C vacancies is crucial for hydrogen trapping in VC precipitates. • Diffusion barrier of hydrogen in VC is 0.63–0.78 eV, consistent with experiments. • Electron gas channels enable hydrogen diffusion through adjacent C vacancies. [ABSTRACT FROM AUTHOR]

In the field of hydrogen storage and transportation, the development of hydrogen barrier coatings with excellent hydrogen permeation resistance is crucial for reducing hydrogen-induced damage caused by hydrogen leakage and hydrogen embrittlement. In recent years, benefiting from its excellent hydrogen barrier performance and wide application range, polymer-based hydrogen barrier composite coatings, membrane and films are expected to become an essential technology in promoting efficient hydrogen storage and transportation in the future. Primarily, starting from the material design of the composite systems, commonly applied gas barrier polymers and two-dimensional nanofillers are explicitly outlined. The detailed data of hydrogen barrier performance as well as advantages and disadvantages of their applications in this field are analysed and highlighted, and strategies are conceived and proposed to optimize their hydrogen barrier performance. Then, the major factors influencing the performance of hydrogen barrier composite system are put forward, providing ideas for strengthening the performance of hydrogen barrier composite from diverse perspectives and exploring failure mechanisms. Finally, a systematic classification overview of the currently researched hydrogen barrier composite system has been provided, and based on their different categories, the development trend of how to achieve large-scale applications of these coatings in the future is discussed. The H 2 barrier composite membrane, coating & film exhibit tremendous application prospects in abundant hydrogen-related fields. [Display omitted] • The H 2 barrier composites for efficient H 2 transportation and storage are discussed. • Major gas barrier polymers are explicitly summarized. • Common two-dimensional gas barrier fillers are outlined and compared. • Future development and optimization of H 2 barrier composites are envisioned. [ABSTRACT FROM AUTHOR]

Atom probe tomography (APT) is a promising tool to measure the atomic-scale distribution of hydrogen in solid matter for the assessment of hydrogen embrittlement susceptibility of materials. However, the accuracy of such measurements resulting from ambient charging and transfer experiments needs to be established. In this work, APT quantification of hydrogen (H) and deuterium (D) in a typical X65 pipeline steel has been determined after ambient charging and transfer to ascertain the contribution of artifacts to the measured H/D signal. A series of experimental workflows related to sample preparation (electropolishing, focussed ion beam) and electrochemical charging conditions (different electrolytes and charging potentials) were explored for H/D measurement using APT. The results show that APT can be used to measure charged H/D with statistical confidence after ambient charging and transfer, that hydrogen ingress occurs during electropolishing, and using a more negative charging potential will introduce more H/D into the material. [ABSTRACT FROM AUTHOR]

First-principles study is used to comparatively study the hydrogen embrittlement resistance, elastic properties, and electronic structures of VWH and VMoH phases with various W and Mo concentration. Calculations reveal that the VMo phases have lower hydrogen solubility compared to VW phases, leading to higher hydrogen embrittlement resistance in VMo. In addition, the concentrations of W and Mo above 0.1875 would enhance the hydrogen embrittlement resistance of V membrane. Conversely, the W or Mo concentrations below 0.1875 would reduce the hydrogen embrittlement resistance. It is also demonstrated that adding W and Mo at concentrations below 0.25 would reduce the solid-solution strengthening of VH phase, thereby reducing its brittleness. This study will enhance comprehension of the underlying physics of VWH and VMoH phases and align with existing experimental literature. • Adding Mo is more effective than adding W in improving the hydrogen embrittlement resistance of V membrane. • The concentrations of W or Mo above 0.1875 would enhance the hydrogen embrittlement resistance of V membrane. • The W or Mo concentrations below 0.1875 would reduce the hydrogen embrittlement resistance. • Adding W and Mo at concentrations below 0.25 would reduce its brittleness. [ABSTRACT FROM AUTHOR]

In this research, wear resistance of chromium nitride (CrN) coated aluminum alloy with hydrogen charging was investigated. Delamination rates of the CrN coating layer after 6 and 12 h of hydrogen charging were measured to be 42.37% and 86.96%, respectively. In particular, damage by hydrogen attack was observed in the exposed area of aluminum alloy. Increasing in applied load and hydrogen charging time decreased the friction coefficient, and when the two factors interacted, a significantly higher increasing rate of wear damage was observed. The increasing rate in wear depth due to hydrogen charging was greater at the applied of 1 N than at 5 N. This is because hydrogen permeation affects the wear resistance of the CrN coating layer and aluminum alloy in the depth direction. In addition, re-transfer and re-adhesion of the CrN coating, whose adhesion strength had decreased due to hydrogen charging, actively occurred. • The high durability of hydrogen valve is a very important factor for the commercialization of fuel cells. • The surface damage and delamination of the CrN coating layer by hydrogen charging were obviously observed. • The delamination of the CrN coating layer occurred in a bulk, and the wear resistance decreased accordingly. • In particular, hydrogen charging affected the adhesive wear of CrN-coated specimens. • Nevertheless the CrN coating technology is significantly excellent performance for resistance of hydrogen embrittlement. [ABSTRACT FROM AUTHOR]

The influence of hydrogen on the fracture of X65 was studied. The fracture toughness in air was 369 MPa√m. The ASTM-valid fracture toughness with cathodic hydrogen charging was lower but was similar for these charging conditions 189 MPa√m and 181 MPa√m at 9 mA/cm2; 192 MPa√m and 179 MPa√m at 16 mA/cm2; and 177 MPa√m at 25 mA/cm2; even though the fractography changed from (i) ductile fracture by microvoid coalescence in air and at 9 mA/cm2 to (ii) more brittle fracture for hydrogen charging at 16 mA/cm2 and 25 mA/cm2, with flat facets and secondary cracks, which increased with increasing current density. • The influence of hydrogen on the fracture of X65 was studied. • The fracture toughness in air was 369 MPa√m. • The ASTM-valid fracture toughness with cathodic hydrogen charging was lower. • The fracture toughness with hydrogen was 152–186 MPa√m. • The fractography changed from ductile fracture to more brittle fracture with increasing hydrogen. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to provide a highly efficient method to obtain the kinetics of the hydrogen evolution reaction (HER) on metal electrodes in an alkaline solution and to analyze the effect of thiourea addition on HER under the same cathodic overpotential. Design/methodology/approach: A novel method based on hydrogen permeation tests, potentiodynamic polarization tests and electrochemical impedance spectroscopy was put forward to characterize the HER kinetics on metal electrode. Findings: The study found that adding thiourea accelerated the Volmer, Heyrovsky and Tafel reactions associated with HER. In addition, it reduced the hydrogen surface coverage and increased the hydrogen permeation steady-state current density. As a result, thiourea facilitated HER, promoted the diffusion of hydrogen atoms into iron and reduced the number of hydrogen atoms in the adsorbed state. Originality/value: This work provides novel insights into the influence of thiourea on HER kinetics, demonstrating that thiourea addition can significantly enhance HER efficiency by altering reaction dynamics and promoting hydrogen atom diffusion into iron. This has implications for hydrogen energy applications, cathodic protection and understanding hydrogen embrittlement mechanisms. [ABSTRACT FROM AUTHOR]

Purpose: In this paper, the authors aim to study the relationship between hydrogen embrittlement (HE) susceptibility and cathodic current density applied on the X70 steel girth welds. Design/methodology/approach: The HE susceptibility of X70 steel girth welds were investigated through slow strain rate tensile test and observed and analyzed by optical microscope and scanning electron microscope methods. Findings: The results show that HE susceptibility of X70 girth weld was basically unchanged with increasing of ion concentration while gradually increased and maintain at a specific value with the increase of cathodic current density. As for same ion content, a dense calcareous deposit layer generated on the sample surface in soil simulation solution with Ca2+ and Mg2+ resulted a decreased HE susceptibility while the porous calcareous deposit layer resulted a increased HE susceptibility. Originality/value: A logistic regression model was established to describe the correlation between HE index and the cathodic current density. [ABSTRACT FROM AUTHOR]

In this work, the effects of Nb micro-alloying on the stress corrosion cracking (SCC) behaviors of the heat-affected zone (HAZ) of high-strength low-alloy (HSLA) steel exposed to SO2-polluted seawater were investigated using electrochemical measurements, static load U-bend immersion tests and slow strain rate tensile experiments combined with fractographic observations. Results indicated that Nb existed in solute status in the coarse-grained HAZ (CGHAZ) while simultaneously in the form of solute status and NbC precipitate in the fine-grained HAZ (FGHAZ) and inter-critical HAZ (ICHAZ). With reduced prior austenite grain sizes, Nb micro-alloying refined the lath bainite in the CGHAZ as well as induced the formation of acicular ferrite in the FGHAZ and granular bainite in the ICHAZ. Moreover, the three types of HAZ microstructures had a high SCC susceptibility in SO2-polluted seawater in the increasing order of ICHAZ < FGHAZ < CGHAZ under the combined mechanism of anodic dissolution and hydrogen embrittlement. Nevertheless, attributing to the variations of microstructural constituents and the presence of NbC precipitates, Nb micro-alloying was capable to enhance the SCC resistance of HAZ microstructures by inhibiting the initiation and propagation of SCC cracks, with the SCC susceptibility decreased by ~ 5%, ~ 28% and 24% for CGHAZ, FGHAZ and ICHAZ, respectively. [ABSTRACT FROM AUTHOR]

A theoretical model was established to investigate the interaction between hydrogen clusters and edge dislocations emitted from a semi-elliptical surface crack tip in deformed nanometallic materials. The model's solution was obtained by using the complex method, and the influence of the concentration and location of hydrogen clusters, temperature, crack shape, material constants, and the dislocation emission angle on the critical stress intensity factor (SIFs) corresponding to the first dislocation emission from crack tips was investigated through numerical analysis. The results show that dislocations are easily emitted from the crack tip at high hydrogen concentration, and hydrogen clusters close to the crack tip will hinder the emission of dislocations from its crack tip. When considering the influence of hydrogen cluster, an increase in temperature, an extension of crack length or an increase in crack tip curvature radius can all make the emission of dislocations at the crack tip difficult, thereby reducing the toughness of the material caused by dislocation emission. [ABSTRACT FROM AUTHOR]

The integration of hydrogen into natural gas pipelines presents challenges due to Hydrogen Embrittlement (HE), requiring critical material selection and testing methods. One such test is the Disk Pressure Test (DPT), which consists in pressurizing a clamped disk to failure. However, failure happens often at the clamping zone, making analysis difficult. This study aims to develop new disk geometries to control failure location while maintaining the test setup. Using two steel grades (a vintage X52 pipeline steel and a modern E355 modified steel with potential for pipeline use), new disk geometries were tested under helium and hydrogen at various pressure rise rates. Results show successful displacement of failure away from the clamping zones, demonstrating the effectiveness of the new geometries. Hydrogen embrittlement is demonstrated by comparing failure pressures under helium and hydrogen at various pressure rise rates. Using both material testing and simulation, this study provides insights into hydrogen embrittlement. • New disk geometries: Specimens redesigned to shift failure from clamping zones. • Hydrogen embrittlement: Pressure tests showed similar rupture pressures and depths. • Simulation: Models linking hydrogen trap density to plastic strain matched results. • Trap binding energy and trap density evolution matching embrittlement depth. • Modified geometries enable distinct stress states for hydrogen embrittlement studies. [ABSTRACT FROM AUTHOR]

The effect of plastic deformation on the hydrogen embrittlement behavior of high-strength martensitic steels was investigated using a U-bend test. The hydrogen embrittlement susceptibility appeared to be enhanced with increasing plastic strain. Based on fractographic and stress-strain analyses, the maximum principal stress dominated the hydrogen embrittlement fracture. Although an apparent enhancement with increasing plastic deformation was observed, the origin of this enhancement was increased residual stress arising from the evolution of graded plastic strain during U-bending. We conclude that residual stress, rather than plastic strain induced by plastic deformation strongly affects hydrogen embrittlement susceptibility in deformed high-strength steel components. • Hydrogen embrittlement susceptibility of U-bend specimens was independent of plastic strain. • Maximum principal stress was the primary criterion for the hydrogen embrittlement susceptibility. • The apparent decrease in hydrogen embrittlement resistance with reduced bending radii was due to increased residual stress. [ABSTRACT FROM AUTHOR]

The influence of simulated reheated coarse-grained heat-affected zones (CGHAZ) on the microstructural evolution and hydrogen embrittlement in high-strength naval steel was investigated by scanning electron microscopy, microhardness testing, electron backscatter diffraction, slow strain rate tensile test and fracture morphology analysis. Twinned martensites were observed in both the intercritical and super-critically reheated CGHAZ, with a widely spaced region in the former. Intercritical reheated coarse-grained HAZ (ICCGHAZ) was the weakest zone of reheated CGHAZ when the peak temperature was 660 °C, exhibiting the intergranular cracking feature. Twinned martensite and coarsening grain size were therefore concluded to be the main reasons for high hydrogen embrittlement susceptibility in the reheated CGHAZ. • The microstructural evolution in different regions of reheated HAZ was investigated. • Twinned martensite was the susceptible microstructure to hydrogen embrittlement. • Second peak temperature affected the formation of twins. • Inter-critical reheated CGHAZ was the weakest zone of reheated HAZ. [ABSTRACT FROM AUTHOR]

In this study, the effect of dislocation and grain boundary (GB) on hydrogen embrittlement of aluminum alloys was investigated using pre-strain and molecular dynamics (MD). Hydrogen increased the yield strength (YS) and ultimate tensile strength (UTS) of pre-strain alloys. MD simulations revealed that hydrogen enhance the critical resolved shear stress (CRSS) for dislocation, and hydrogen segregation GB reduce material strength. The YS and UTS of Al alloys are affected by both mechanisms during deformation, and the two mechanisms exhibit a competitive relationship. Hydrogen enhanced CRSS dominates in higher dislocation density deformations. [Display omitted] • H increase the YS and UTS of pre-strain 7075 Al alloys. • H has a pinning effect on dislocation and enhanced the CRSS. • Hydrogen segregation GB reducing the tensile strength of Al. • The YS and UTS of Al are influenced by a combination of two distinct mechanisms. • H enhanced dislocation slip CRSS dominates in higher dislocation density deformation. [ABSTRACT FROM AUTHOR]

The hydrogen embrittlement behavior of a prerolled Fe–15Mn–0.65C–2Al–2Si high‐Mn steel with various cut‐edge properties is studied via hydrogen precharging and slow strain rate test. In the presence of hydrogen, samples prepared by laser cutting under atmosphere of N2 exhibit the best total elongation at about 39%. Press blanking produces severe shear deformation, tensile residual stresses, and strain‐induced martensite, resulting in a high risk to hydrogen‐induced cracking. With compressive residual stresses produced from waterjet, corresponding samples exhibit the lowest elongation loss against hydrogen. Despite hydrogen charging, the fracture surfaces show transgranular quasi‐cleavage features, for which mechanical twinning from prerolling plays a critical role. The hydrogen‐enhanced decohesion mechanism accounts for cleavage fracture since hydrogen segregation reduces cohesive stress at twin boundaries. [ABSTRACT FROM AUTHOR]

Investigating the interaction between hydrogen and dislocations is essential for understanding the origin of hydrogen-related fractures, specifically hydrogen embrittlement (HE). This study investigates the effect of hydrogen on the mobility of ½<111>{110} and ½<111>{112} edge dislocations in body-centered cubic (BCC) iron (Fe). Specifically, molecular dynamics (MD) simulations are conducted at various stress levels and temperatures for hydrogen-free and hydrogen-containing lattices. The results show that hydrogen significantly reduces dislocation velocities due to the pinning effect. Based on the results of MD simulations, phenomenological mobility laws for both types of dislocations as a function of stress, temperature and hydrogen concentration are proposed. Current findings provide a comprehensive model for predicting dislocation behavior in hydrogen-containing BCC lattices, thus enhancing the understanding of HE. Additionally, the mobility laws can be utilized in dislocation dynamics simulations to investigate hydrogen-dislocation interactions on a larger scale, aiding in the design of HE-resilient materials for industrial applications. [Display omitted] • Effect of hydrogen and temperature on the mobility of edge dislocations is studied. • The effect of hydrogen on kink-pair formation and propagation is discussed. • Thermally activated mechanisms and viscous damping dynamics are discussed. • Hydrogen decreases the mobility of both dislocations via pinning effect. • Hydrogen-induced phenomenological mobility laws are proposed. [ABSTRACT FROM AUTHOR]

Small-hole components of Inconel 718 are widely used in aerospace engineering, medical devices, and other fields. Limited by material properties, its machining efficiency seriously restricts its wide application. The objective of this study is to investigate a novel machining technique for Inconel 718 that integrates ultrasonic machining (UM) and hydrogen embrittlement (HE) treatment. Accordingly, the technique is designated as hydrogen embrittlement-enhanced ultrasonic machining (HEUM). Prior to machining, a stress layer is formed on the surface of the workpiece. To ascertain the fundamental characteristics of Inconel 718, the influences of ultrasonic amplitude, HE time, and HE voltage on the specific material removal rate and surface roughness in the presence of HE were empirically examined. To investigate the material removal process for HEUM, the nanoscratch test and nanoindenter were also conducted with HE samples. Further, the subsurface for HEUAG samples were obtained with SEM. The specific material removal rate under experimental conditions of 10 min and 5 V HE increased by 27.4%. Finally, HEUM is proposed to be used for a 1 mm through-hole with Ra 0.318 μm. A precision hole with a diameter as small as 0.5 mm has been manufactured. [ABSTRACT FROM AUTHOR]

The susceptibility of subzones of the coarse-grained heat-affected zone (CGHAZ) in X65 pipeline steel to hydrogen embrittlement was studied through an in situ crack-tip opening displacement test in an H 2 S-containing environment. The intercritically reheated CGHAZ (IC-CGHAZ) exhibited the highest embrittlement factor of 89.4%, compared to 64.0% for the sub-critically reheated CGHAZ (SC-CGHAZ). Hydrogen transportation by dislocations to massive-slender martensite/austenite (M/A) constituents initiated cracks in IC-CGHAZ. Deterioration of lath bainite (LB) boundaries, with separation of M/A-ferrite interface, accelerated crack propagation across prior austenite grains and promoted hydrogen-assisted degradation of fracture toughness. Reheated CGHAZ at a peak temperature of 620 °C led to an increased intensity of the {110} LB boundary texture by up to 52% in SC-CGHAZ. This enhanced texture facilitated dislocation slipping along {110} LB boundary planes, thereby promoting deformation compatibility and preventing the deterioration of LB boundaries in the presence of hydrogen. • SC-CGHAZ exhibits the lowest embrittlement factor of 64.0% in H 2 S. • Reheated CGHAZ at 620 °C leads to increased {110} LB boundary texture by up to 52%. • {110} LB boundary significantly influences cracking associated with hydrogen. [ABSTRACT FROM AUTHOR]

This work is aimed at a comprehensive solution to the problem of reliable and safe operation of a transport energy system with a high energy concentration based on a universal energy carrier - cryogenic liquid hydrogen. The article discusses the possibility of using various methods and techniques to assess the reliability of machines and equipment operated in emergency situations and extreme conditions. The obtained results are analyzed. Currently, the oil and gas complex pays great attention to the development of hydrogen technologies, as well as hydrogen energy in connection with the relevance of the Climate Agenda. In this regard, hydrogen energy facilities are of the greatest interest: cryogenic hydrogen reservoirs, cryogenic hydrogen pipelines, cryogenic oxygen reservoirs and cryogenic oxygen pipelines, as well as cryogenic reservoirs and pipelines for storing process nitrogen gas. An important role for global energy exchange is played by LH 2 tankers for transporting cryogenic hydrogen. For example, Australia and Japan built the first LH 2 tanker to transport hydrogen from Australia to Japan. In addition, another 85 LH 2 tankers are expected to be built. After transportation, cryogenic hydrogen is stored in cryogenic hydrogen storages, usually also representing cryogenic hydrogen tanks with piping in the form of cryogenic pipelines, as well as cryogenic nitrogen tanks for storing process nitrogen gas. Further, hydrogen is used in road transport, aviation, ship fleet, industry, and energy. The main elements of mobile, stationary and airborne hydrogen storage systems are under critical loads and are in the area of increased study and attention. In this regard, we considered the functions of changing the main operational characteristics, made proposals on the possibility of predicting the development of accumulated faults and proposals for ensuring safety and extending the life of objects, taking into account the determination of local and integral damage to cryogenic tanks and pipelines. Project for the creation of a main cryogenic hydrogen pipeline from Azerbaijan to Europe across the Adriatic Sea. [Display omitted] [ABSTRACT FROM AUTHOR]

A hydrogen economy will require the use of steel pipelines to transport and store hydrogen. Methods and materials are urgently needed to prevent the embrittlement of steel pipelines in hydrogen service. In this work, we show that hydrogen permeation into pipeline steel can be mitigated by organic inhibitors, as demonstrated by a typical organic inhibitor benzotriazole (BTA) under simulated X65 steel pipeline cathodic protection conditions. Electrochemical and surface analytical techniques were used to probe the efficiency and mechanism of hydrogen permeation inhibition. In particular, a novel multi-electrode array method was designed to probe the inhibitor film by measuring local impedance and hydrogen charging currents. The ability and efficiency of BTA to inhibit hydrogen permeation were found to be closely associated with the formation and coverage of inhibitor films on steel surfaces. A model is proposed to illustrate the mechanism of hydrogen permeation inhibition by organic inhibitors. • The efficiency and mechanism of an organic hydrogen permeation inhibitor is investigated. • A multi-electrode array was used to probe the inhibitor film formation and coverage. • The capability of hydrogen permeation inhibition is related to inhibitor film formation. • The efficiency of hydrogen permeation inhibition is affected by inhibitor film coverage. • A model is proposed to explain the mechanism of hydrogen permeation inhibition. [ABSTRACT FROM AUTHOR]

With the increasing focus on reducing carbon emissions, hydrogen has emerged as a promising alternative energy source. However, the safe transportation of hydrogen poses challenges due to its potential impact on the integrity of pipeline materials. This study aims to investigate the effect of hydrogen charging time on the plastic behavior and ductile fracture characteristics of API 5L X42 pipelines, which are commonly used for transporting hydrocarbons. Tensile tests were conducted on various types of hydrogen-charged specimens at room temperature to assess different fracture modes. Hydrogen was introduced into the specimens using a cathodic electrolytic method, and 24-h charging time durations were considered. Finite element analyses were performed on standard dog-bone and notched tension specimens to evaluate the plastic behavior, employing the Swift hardening law to model the flow stress. Numerical analyses were conducted to determine the loading path leading to fracture initiation. A damage framework based on the Hosford–Coulomb model was utilized to predict ductile fracture under non-proportional loading conditions. The findings of this study provide insights into the fracture behavior of pipelines under hydrogen exposure, aiding in the design and assessment of safe and reliable hydrogen transport systems. [ABSTRACT FROM AUTHOR]

This study investigates the hydrogen embrittlement behavior of API X70 linepipe steel. The microstructure was primarily composed of a dislocation-rich bainitic microstructure and polygonal ferrite. Slow strain-rate tests (SSRTs) were performed under both ex situ and in situ electrochemical hydrogen charging conditions to examine the difference between hydrogen diffusion and trapping behaviors. The ex situ SSRTs showed almost the same tensile properties as air and a limited brittle fracture confined to near the surface. In contrast, the in situ SSRTs showed an abrupt failure after the maximum tensile load, leading to a brittle fracture across the entire fracture surface with stress-oriented hydrogen-induced cracking (SOHIC). The crack trace analysis results indicated that SOHIC propagation paths were influenced by localized hydrogen accumulation due to high-stress fields. As a result, the dominant hydrogen embrittlement mechanisms, such as hydrogen-enhanced localized plasticity (HELP) and hydrogen-enhanced decohesion (HEDE), changed. These findings provide critical insights into the microstructural factors affecting hydrogen embrittlement, which are essential for the design of hydrogen-resistant steels in hydrogen infrastructure applications. [ABSTRACT FROM AUTHOR]

In this study, the harmful effects of a banded structure on the bending fracture of electroplated fasteners are investigated. The origins and ways to control these structures are also explored. The fracture surfaces of the fasteners exhibit stepwise cracks and numerous intergranular facets associated with ductile tearing, which is a characteristic of hydrogen embrittlement. The origin of these stepwise cracks can be traced to the internal banded structures. Therefore, the internal banded structures promote fracturing during the bending test. The internal banded structures in the fasteners can be traced back to the internal cracks in the bloom, and inappropriate soft‐reduction processes lead to internal cracks. Notably, the carbon segregation at the internal cracks is severe. This is attributed to the proximity of the internal cracks to the center of the bloom, causing the enriched liquid in the interdendritic region to be sucked into these internal cracks. The optimal reduction position and amount are determined by employing heat‐transfer and soft‐reduction models. Fluctuations in superheat and casting speed significantly influence this optimal position and reduction amount. [ABSTRACT FROM AUTHOR]

This study delves into effects of deep cryogenic treatment (DCT) on enhancing the hydrogen embrittlement resistance of CoCrFeMnNi high-entropy alloy fabricated via laser powder-bed-fusion (L-PBF). Comparatively assessing as-print, conventional heat treatment, and DCT, we uncover how nanotwin formation within matrix serves as a critical mechanism to combat adverse effects of hydrogen embrittlement. This work reveals that DCT not only mitigates inherent residual stresses from L-PBF, thereby fostering dislocation redistribution and microstructural stabilization, but also synergizes with high-density dislocation cells. Our findings articulate a nuanced understanding of microstructural evolution in response to post-treatments and consequential enhancement of hydrogen embrittlement resistance. Laser-based additively manufactured CoCrFeMnNi undergoes post heat treatment and deep cryogenic treatment to tailor dislocations and residual stress. The inherent residual stress acts as the driving force for the redistribution of dislocations, leading to the development of a stable microstructure after deep cryogenic treatment. High-density dislocation cells and hydrogen collaborate to lower the local stacking fault energy, triggering gradient nanotwins. Nanotwin-ability effects by deep cryogenic treatment (77 K × 36 h) on the hydrogen embrittlement resistance of CoCrFeMnNi with interior defects are verified. [ABSTRACT FROM AUTHOR]

Most of the conventional welding process induces Welding Residual Stress (WRS), hydrogen embrittlement and distortions to welded components. The post-weld mechanical behaviour has an impact on both structural integrity and operational effectiveness of the welded component. Traditional Post Weld Heat Treatment (PWHT) is capable of relieving WRS to some extent. Based on recent research, Heat Treatment (HT) cycles are comprised of conventional HT and Cryogenic Treatment (CT) gives better fatigue life to welded components by redistributing the residual stress field. There is a need for further research to explore the impact of different parameters of CT affects the mechanical behaviour of welded specimens. In this study, numerical and experimental investigations are conducted to understand the impact of HT cycles comprised of austenitizing, quenching, CT and tempering process, over the TIG welded EN8 plates. Numerical model is developed for predicting the variation in WRS with each stage of HT cycles and observed a considerable redistribution of WRS after the completion of proposed HT cycle. Using the proposed HT cycle, the influence of different soaking periods of CT over the welded components are studied experimentally and shows that 36 hours soaking period have higher impact on the welded component's mechanical behaviour. [ABSTRACT FROM AUTHOR]

With the global energy transition and increasing environmental requirements, hydrogen-mixed gas turbines as a high-efficiency and low-emission energy conversion equipment has been widely concerned. This paper reviews the development status of hydrogen-mixed gas turbines domestically and internationally, analyzes the characteristics of hydrogen combustion in gas turbines, explores the impact of hydrogen combustion on complex components and the application of high-temperature materials, and analyzes the performance requirements for hot-end component materials operating under high temperature, high pressure, and corrosive conditions, as well as the main challenges and potential solutions in current material development. The effects of water vapor and hydrogen embrittlement during hydrogen combustion on gas turbine alloys and thermal barrier coatings are discussed in detail. Water vapor accelerates the oxidation and corrosion of alloys, leading to a decline in mechanical properties. Furthermore, hydrogen embrittlement significantly affects the toughness and durability of alloys, increasing the risk of crack propagation and fracture. In terms of the problems, future research should focus on multi-field coupling simulations and accelerated corrosion tests, considering the factors such as temperature, pressure, and different atmospheres to establish realistic environment simulators to evaluate alloy and coating performances. Additionally, the combined effects of hydrogen and water vapor on high-temperature alloys and thermal barrier coatings should be emphasized. This includes investigating the diffusion mechanisms of hydrogen in alloys, interactions with lattice defects, and the microscopic processes leading to hydrogen embrittlement. Building oxidation models in high-temperature water vapor environments, clarifying the dissociation and adsorption mechanisms of water vapor at high temperatures, the hydroxylation of protective oxide films Al2O3 and Cr2O3, and the growth behavior of non-protective oxides(e.g., spinel) are also essential. [ABSTRACT FROM AUTHOR]

This study investigates the role of coalesced bainite in enhancing the hydrogen embrittlement resistance of tempered martensitic steels. By analyzing the microstructural characteristics and mechanical properties under varying cooling rates, it was found that the presence of coalesced bainite significantly impedes hydrogen accumulation at prior austenite grain boundaries. This leads to a transition in the fracture mode from intergranular to transgranular, thereby improving the overall resistance to hydrogen embrittlement in steels. Slow strain rate tests (SSRTs) on both smooth and notched specimens further confirmed that steels cooled at lower rates, which form a higher fraction of coalesced bainite, exhibiting superior hydrogen embrittlement resistance. These findings suggest that optimizing the cooling process to promote coalesced bainite formation could be a valuable strategy for enhancing the performance of tempered martensitic steels in hydrogen-rich environments. [ABSTRACT FROM AUTHOR]

The influence of the centerline segregation region (CSR) on the hydrogen embrittlement (HE) of two different API 5L X80 pipeline steel plates was investigated. The novelty of this work was to establish relationships between the CSR, microstructure, and distribution of localized fragile particles on HE susceptibility and on fracture morphology. This work intended to establish a relationship between centerline segregation and HE susceptibility in high-strength low-alloy steels submitted to inhomogeneous transformations. Microscopy, hydrogen permeation, and slow strain rate (SSR) tests were used to investigate hydrogen-related degradation. The solution used on the charging cell of the permeation tests—and on the SSR test cell—was 0.5 mol L−1 H2SO4 + 10 mg L−1 As2O3, and in the oxidation cell, 0.1 M NaOH was used as a solution. The CSR led the thicker plate to present the highest HE index (0.612) in analyses carried out in the mid-thickness; however, the same plate showed the lowest HE index in near-surface tests. The presence of hydrogen changed the fracture morphology from ductile to a brittle and ductile feature; this occurred due to the interaction with localized fragile particles and the significant reduction of the shear stress necessary for the dislocation movement. [ABSTRACT FROM AUTHOR]

This study employs a custom hollow specimen setup to investigate the HE in API 5L X60 pipeline base and welded materials exposed to pure hydrogen and a 20% hydrogen–natural gas blend at 2.07 MPa. Results indicate embrittlement with increasing hydrogen concentration. The base material showed a hydrogen embrittlement index (HEI) of 11.6% at 20% hydrogen and 12.4% at 100% hydrogen. For the welded material, the HEI was 14.6% at 20% hydrogen and 18.0% at 100% hydrogen. Fractography analysis revealed that the base and welded materials exhibited typical ductile fracture features in the absence of hydrogen, transitioning to a mixture of quasi-cleavage and micro-void coalescence (MVC) features in hydrogen environments. Additionally, with hydrogen, increased formation of secondary cracks was observed. Notably, the study identified the Hydrogen-Enhanced Localized Plasticity (HELP) mechanism as a probable contributor to hydrogen-assisted fracture. [ABSTRACT FROM AUTHOR]

The utilization of micro-sample testing has demonstrated its effectiveness in conducting quantitative research on mechanical properties, damage evolutions and fracture features. For in-service equipment, millimicron sampling allows for non-destructive testing and analysis of mechanical performance evolution during operation. This paper presents a comparative study of the miniature uniaxial tensile test (MUTT) and small punch test (SPT) by experimental and finite element methods. As a comparison, the standard conventional-size tensile tests were also carried out. Detailed analyses of the elastoplastic behaviors and damage evolutions of MUTT and SPT were presented, followed by an application case illustrating the characterization of hydrogen embrittlement sensitivity based on MUTT and SPT. An inverse finite element modeling method of load–displacement curve reproduction was used to calibrate the variations of damage parameters of hydrogen-charged MUTT and SPT specimens. Hydrogen embrittlement (HE) indexes were determined by using different calculation methods. The results reveal that the HE sensitivity estimated by MUTT is higher than that measured by SPT, which is related to the different deformation processes and strain rates of the two testing methods. [ABSTRACT FROM AUTHOR]

Hydrogen barrier coatings with Al2O3 as the main component are a good choice for solving the hydrogen embrittlement problem during hydrogen transportation in long-distance pipelines. However, the difference in the coefficients of thermal expansion between the substrate and the Al2O3 coating limits its further utilisation and development. In this study, rare earth oxides were added to the molten aluminium solution, and a Fe-Al transition layer was introduced on the surface of X80 steel by hot-dip plating to solve the thermal mismatch. Here, the microstructure and bonding strength of the hot-dip aluminium layer were investigated. It is found that the hot-dip aluminium coating consists of the outermost aluminium-rich layer and the inner Fe-Al alloy layer, and the microstructure of the two will change with the change in dip plating parameters. The best overall performance of the hot-dip aluminium layer was obtained from X80 steel substrate at a dip plating temperature of 700 °C and a dip plating time of 5 min. This coating has a good interface, moderate thickness, and a bond strength of 49 N. This study provides a reference value for solving the thermal mismatch between the steel substrate and the Al2O3 hydrogen barrier coating generated by subsequent anodising. [ABSTRACT FROM AUTHOR]

The scientific literature is rife with conflicting reports regarding the effect of dissolution on fracture. The complexity arises, in part, due to dissolution often being intertwined with various other mechanisms such as hydrogen embrittlement and the formation of debris behind an advancing crack, which can obfuscate the sole contribution of dissolution. Here, we report on the effect of dissolution when acting in isolation via the utilization of an efficient atomistic-based multiscale modeling technique and a specialized interatomic potential. Our results reveal a dual role of dissolution on crack behavior, introducing an additional layer of complexity to the mechanistic basis of environmental effects. This finding, while challenging for engineering prognosis, provides a route for engineering improved materials. Recognizing and navigating this duality could be pivotal to precluding potentially disastrous consequences in a broad array of engineering applications, from harnessing earth's energy resources to aerospace technologies. [ABSTRACT FROM AUTHOR]

Hydrogen, the lightest and most abundant element in the universe, plays essential roles in a variety of clean energy technologies and industrial processes. For over a century, it has been known that hydrogen can significantly degrade the mechanical properties of materials, leading to issues like hydrogen embrittlement. A major challenge that has significantly limited scientific advances in this field is that light atoms like hydrogen are difficult to image, even with state-of-the-art microscopic techniques. To address this challenge, here, we introduce Atom-H, a versatile and generalizable machine learning-based framework for imaging hydrogen atoms at the atomic scale. Using a high-resolution electron microscope image as input, Atom-H accurately captures the distribution of hydrogen atoms and local stresses at lattice defects, including dislocations, grain boundaries, cracks, and phase boundaries. This provides atomic-scale insights into hydrogen-governed mechanical behaviors in metallic materials, including pure metals like Ni, Fe, Ti and alloys like FeCr. The proposed framework has an immediate impact on current research into hydrogen embrittlement and is expected to have far-reaching implications for mapping "invisible" atoms in other scientific disciplines. [ABSTRACT FROM AUTHOR]

The microstructure and hydrogen embrittlement sensitivity of two X65 pipeline steels at different t 8/5 (the time required to cool from 800 °C to 500 °C) were investigated employing thermal simulation. With the increase of t 8/5 for both steels, the martensite transferred to acicular ferrite (AF) and bainite, and further converts to bainite and martensite/austenite (M/A) constituents. Elongated polygonal Mn–Nb–S inclusions appear in steel A, which are easy to fall off and the hydrogen embrittlement sensitivity is thus increased. However, spherical Al–Ca–Nb–N–O–S inclusions appear in steel B, which can promote nucleation of AF, thus obtaining lower hydrogen embrittlement sensitivity under lower t 8/5. • The HE sensitivity of two X65 pipeline steels at different t 8/5 were investigated. • The elimination of M and the nucleation of AF can reduce HE sensitivity. • Elongated polygonal Mn–Nb–S inclusions easily shed and increase HE sensitivity. • Spherical Al–Ca–Nb–O–S inclusions promote AF nucleation and reduce HE sensitivity. [ABSTRACT FROM AUTHOR]

Hydrogen segregation behaviors at BCC-Fe Σ3 (111) grain boundary (GB) as well as the effects of alloying solutes were studied by the first-principles method. The segregation energy of alloying solutes at different periods presents a concave-down parabolic-like relationship with the atomic number, and the 4 d transition alloying solutes show a higher averaged segregation tendency. At the favorable trapping site, hydrogen segregation energy decreased by increasing the number of hydrogen atoms up to 0.85/Å2 in the plane vertical to the GB. Mo, Tc, Ru, Ta, W, Re, Os, and Ir strengthen GB and inhibit hydrogen segregation. Significantly, the interaction between alloying solutes and hydrogen segregation was elucidated by emphasizing the separation of the chemical and the mechanical contributions, and appropriate descriptors on hydrogen segregation energy influenced by alloying solutes were screened. This work offers theoretical backing to comprehend hydrogen segregation behaviors and the effects of alloying solutes to design advanced high-strength steels resistant to hydrogen embrittlement. • Hydrogen segregation behaviors at pure BCC Σ3 (111) grain boundary were studied. • Alloy solute segregation behaviors at pure BCC Σ3 (111) grain boundary were studied. • Interaction between alloying solutes and hydrogen at grain boundary was elucidated. • Descriptors on hydrogen segregation energy at grain boundary were screened. • Relationship between hydrogen segregation at grain boundary and HE was discussed. [ABSTRACT FROM AUTHOR]

Hydrogen embrittlement (HE) is a significant challenge to the safe operation of hydrogen-blended natural gas pipelines. The mechanical properties of X80 steel were studied after H 2 pre-charging followed by mechanical properties tests and fracture morphologies observation. Results indicated that the hydrogen saturation time of X80 steel was roughly 48 h. H 2 pre-charging induced a decline in strength, plasticity, and fatigue properties, while hydrogen-assisted fatigue crack growth occurred during the early stage of fatigue crack growth rate tests. Additionally, the fracture morphologies transited from primary microvoid coalescence to a mixed mode characterized by ductile dimples and quasi-cleavage planes with increasing hydrogen. The HE susceptibility increased with increasing hydrogen partial pressure and decreasing loading frequency, but there existed a critical value (6 × 10−7 s−1) for the strain rate effect on the HE susceptibility. Under H 2 pre-charging conditions, the predominant HE mechanism was the hydrogen-enhanced local plasticity (HELP) mediated hydrogen-enhanced decohesion (HEDE) mechanism. • Permeation parameters of X80 steel were obtained through H 2 permeation tests. • The mechanical properties of hydrogen pre-charged X80 steel were obtained. • 6 × 10−7 s−1 was determined as the critical strain rate to HE susceptibility. • The predominant HE mechanism under hydrogen pre-charging conditions was analyzed. [ABSTRACT FROM AUTHOR]

This work investigates the hydrogen embrittlement (HE) behavior of Nickel-201 alloy using experimental and numerical approaches. In experimentation, the effect of electrochemical hydrogen charging on the deformation behavior of tensile oligocrystals is investigated at different strain rates. Irrespective of the strain rate levels, all the hydrogen-charged tensile oligocrystals exhibited intergranular (IG) fracture exclusively along the random high-angle grain boundaries (RHAGBs). At the same time, no crack was observed along the coincident site lattice (CSL) Σ 3 type grain boundaries. The absence of an interconnected grain boundary network, lower stress levels, and insensitivity of H-induced IG fracture to the strain rate levels of investigated FCC oligocrystals (with low lattice hydrogen diffusion coefficient) established the insignificance of dynamic H-redistribution toward HE. In numerical simulations, a crystal plasticity-phase field fracture finite element model simulates the macroscopic tensile response and corresponding microscopic fracture evolution behavior for hydrogen-free and hydrogen-charged tensile oligocrystals. The experimental results corroborated by numerical simulations, validate that the reduction in fracture energy of RHAGBs, induced by hydrogen segregation through thermodynamic equilibrium during hydrogen charging prior to deformation, is the dominating factor governing HE. • Hydrogen embrittlement (HE) of Ni- oligocrystals at various strain rate is investigated. • Experimental results are corroborated by crystal plasticity-phase field fracture simulations. • H-induced intergranular fracture initiated and propagated along the RHAGBs only. • H-segregation by thermodynamic equilibrium established prior to deformation governs the HE. [ABSTRACT FROM AUTHOR]

The hydrogen embrittlement (HE) susceptibility of the X52 pipeline steels in simulated hydrogen-blended natural gas (HBNG) environments were investigated with a combination of in situ high-pressure gaseous hydrogen permeation tests, slow strain rate tensile (SSRT) tests and molecular dynamics simulation, the results were compared with the X80 steel. The HE susceptibility of the X52 steel was found higher than that of the X80 steel. The mechanism of the two steels showing different HE susceptibility was analyzed from a point of permeation parameters and molecular dynamics simulation. The results showed that the X52 steel contained more impurity elements and a larger grain size, leading to a higher hydrogen solubility and a microstructure with lower HE resistance. This study suggests that the steel microstructure and the hydrogen permeation property are crucial for the understanding and prediction of the HE susceptibility of the steels. • N 2 partial pressure would not influence the hydrogen permeation behaviour. • HE susceptibility is not necessarily positively correlated with steel grade. • Phase transition/dislocation emission is main deformation mechanism of boundaries. • Hydrogen atom inhibit local energy release and promote crack initiation. • Finer grain weakens the inhibition of local energy release caused by H. [ABSTRACT FROM AUTHOR]

Alloy 625 plays a crucial role in high-pressure hydrogen environments typical of hydrogen refuelling stations, where cyclic temperature and loading conditions prevail. In this study, we reveal that hydrogen-induced ductility loss of nickel-based alloy 625 significant difference which change from 11.9% at slow strain rate to 20.1% at conventional strain rate. The difference can be attributed to a change in deformation mode: from dislocation slipping under slow strain rate to twinning under conventional strain rate. Specifically, hydrogen-refined deformation twins and the promotion of twin bundles under conventional strain rates diminish the twin-induced plasticity effect of the alloy. This shift in deformation mode also alters the hydrogen embrittlement mechanism across the two strain rates. These findings provide valuable insights for hydrogen embrittlement-resistant designing and evaluating hydrogen compatibility for alloy 625. [Display omitted] • The nickel-based alloy 625 has more significant hydrogen-induced ductility loss at 5 × 10−3 s−1 than that at 5 × 10−6 s−1. • The deformation mode change from dislocation slipping at 5 × 10−6 s−1 to twinning at 5 × 10−3 s−1. • Hydrogen weakens the TWIP effect of the alloy because of hydrogen refining DTs. • Hydrogen will promote the formation of deformation twin bundles, resulting in cracking along DTs. • A new mechanism of hydrogen-induced cracking along DTs in nickel-based alloys was proposed. [ABSTRACT FROM AUTHOR]