Hydrogen-induced Embrittlement Research Articles

An approach to coupling the gas flow dynamics and thermodynamics of hydrogen solubility in L485ME steel grade for estimation of fracture toughness

The paper presents the problem of coupling the gas flow dynamics in pipelines with the thermodynamics of hydrogen solubility in steel for the estimation of the fracture toughness. In particular, the influence of hydrogen blended natural gas transmission on hydrogen solubility and, consequently, on fracture toughness is investigated with a focus on the L485ME low-alloy steel grade. Hydraulic simulations are conducted to obtain the pressure and temperature conditions in the pipeline. The hydrogen content is calculated from Sievert’s law and, as a consequence, the fracture toughness of the base metal and heat-affected zone is estimated. Experimental data is used to define hydrogen-assisted crack size propagation in steel as well as to a plane strain fracture toughness. The simulations are conducted for a real natural gas transmission system and compared against the threshold stress intensity factor. The results showed that the computed fracture toughness for the heat-affected zone significantly decreases for all natural gas and hydrogen blends. The applied methodology allows for identification of the hydrogen-induced embrittlement susceptibility of pipelines constructed from thermomechanically rolled tubes worldwide most commonly used for gas transmission networks in the last few decades.

Raman spectroscopy of zirconium hydride

The characterization of zirconium hydride is important in the nuclear industry because of the hydrogen-induced embrittlement of Zircaloy cladding and its use as a neutron moderator. This paper introduces the use of Raman spectroscopy for the characterization of zirconium hydride. First-principles density functional theory (DFT) calculations were used to predict the Raman spectra of ζ-ZrH0.5, γ-ZrH, δ-ZrH1.5, δ-ZrH1.66, and ε-ZrH2 with all their predicted symmetries; ζ-ZrH0.5 (P3m1, R3¯m, C2/m, Cm, Cmmm, and Pn3¯m); γ-ZrH (P222, Ccce, and P42/mmc); δ-ZrH1.5 (P4¯m2, P42/mcm, Fmmm, Pn3¯m, Ibam, P2/c, PI, and P42/nnm); δ-ZrH1.66 (Fm3¯m); and ε-ZrH2 (Fm3¯m, R3¯m, and I4/mmm). Two samples of Zircaloy-4 containing 133 wt ppm and 360 wt ppm hydrogen were characterized by Raman spectroscopy, showing two signal lines at 215 cm−1 and 1,187 cm−1, which were assigned to the presence of δ-ZrH1.66. These signals had a good spatial correlation with visible hydride precipitates in Raman spectroscopy images. This work provides the basis for the characterization of all possible zirconium hydride compositions and structures using Raman spectroscopy.

Hydrogen atom occupancy variation induced fragile to strong transition of titanium hydride

Hydrogen embrittlement is a prevalent issue that restricts the use of titanium as a structural material. To comprehend the hydrogen embrittlement mechanism, it is necessary to investigate the intrinsic mechanical properties of hydrides in titanium. In this study, a fragile to strong transition is observed in δ-TiH2 at 423 K. The in situ high temperature nuclear magnetic resonance measurements reveal that the occupancy of hydrogen atoms undergo a transition from octahedral sites to tetrahedral sites at the same temperature. Further first-principles calculations reveal that the decrease in the generalized stacking fault energy, resulting from the modification in the hydrogen atom occupancy, is the primary reason for the enhancement in the mechanical properties of δ-TiH2. This study suggests comprehending hydride fracture toughness through the lens of hydrogen atom occupancy, providing a novel research perspective on the hydrogen-induced embrittlement mechanism in titanium alloys.

Investigations of temperature effects on hydrogen diffusion and hydrogen embrittlement of X80 pipeline steel under electrochemical hydrogen charging environment

The influence of temperature on hydrogen diffusion and hydrogen embrittlement of X80 steel was studied using electrochemical hydrogen charging. The hydrogen diffusion and subsurface hydrogen concentration in the steel increased with increasing the temperature. Macro slow strain rate tensile tests and microstructural analysis were performed to unveil the dependence of hydrogen-induced embrittlement susceptibility on temperature, which suggested a temperature threshold THE, max of 315 K. The demonstration of THE, max would be crucial for determining test temperatures of hydrogen-related engineering material applications.

Effect of tempering temperature on stress-assisted hydrogen diffusion and hydrogen-induced embrittlement in a high strength low alloy steel

Hydrogen can be used as a probe to detect defects created during tensile tests. Through hydrogen diffusion behavior investigated under two loading ways in a high strength low alloy steel tempered at three different temperatures, the mechanism of embrittlement resulted from dynamic hydrogen charging was elaborated. Before yielding, the stress has no significant effect on the hydrogen diffusivity. However, near yield stress, the hydrogen diffusion varies with sustaining the loaded time, while at the plastic region, the hydrogen diffusivity returns to a relative lower and stable value. In addition, hydrogen solubility monotonously increases with elastic stress in all samples tempered at different temperatures, whereas the plastic stress can differently alter the steady state hydrogen permeation flux from sample to sample depending on the tempering temperature. Hence, all samples tempered at different temperatures can be damaged in advance by dynamic hydrogen charging but the sensitivity to hydrogen embrittlement can still be alleviated by raising tempering temperature.

Hydrogen Embrittlement Failure Behavior of Fatigue-Damaged Welded TC4 Alloy Joints

The interaction between fatigue damage and hydrogen in TC4 welded joints was analyzed considering specimens with different pre-cycles. The fracture failure caused by hydrogen-induced fatigue damage was investigated using tensile testing and microstructural observations. The results indicate that increasing the number of pre-cycles increases the specimens’ initial dislocation density, enhancing the severity of the hydrogen-induced embrittlement phenomenon. The hydrogen-enhanced local plasticity mechanism, manifested by fracture along the grain boundary, dominates the tensile process in fatigue-damaged hydrogen-filled welded joints after 10,000 and 20,000 pre-cycles. After 30,000 pre-cycles, the hydrogen-enhanced decohesion mechanism dominates the tensile process, manifesting as a transgranular cleavage decoupling fracture.

Irradiation Damage Independent Deuterium Retention in WMoTaNbV.

High entropy alloys are a promising new class of metal alloys with outstanding radiation resistance and thermal stability. The interaction with hydrogen might, however, have desired (H storage) or undesired effects, such as hydrogen-induced embrittlement or tritium retention in the fusion reactor wall. High entropy alloy WMoTaNbV and bulk W samples were used to study the quantity of irradiation-induced trapping sites and properties of D retention by employing thermal desorption spectrometry, secondary ion mass spectrometry, and elastic recoil detection analysis. The D implantation was not found to create additional hydrogen traps in WMoTaNbV as it does in W, while 90 at% of implanted D is retained in WMoTaNbV, in contrast to 35 at% in W. Implantation created damage predicted by SRIM is 0.24 dpa in WMoTaNbV, calculated with a density of atoms/cm. The depth of the maximum damage was 90 nm. An effective trapping energy for D in WMoTaNbV was found to be about 1.7 eV, and the D emission temperature was close to 700 °C.

The Features of Heat and Mass Transfer in the Operation of Nuclear-Powered Icebreaker Steam Generators

The problem of hydrogen induced embrittlement of and crack formation in the piping systems of nuclear-powered icebreaker steam generators is considered. Information about the relevance of this problem for ensuring reliable operation of the nuclear power installations of transport facilities and similar systems such as floating nuclear power units is given. Hydrogen accumulation in the steam generator feedwater header pipes welding zone and their subsequent hydrogen-induces embrittlement lead to crack formation. For modeling the hydrogen transport processes from the reactor to the steam generator, two types of computer codes are jointly used: 1D approximation and 3D ones. The performed analysis has identified the main characteristic processes. For solving the problem, it was decomposed into subproblems. The transport of vapor-gas bubbles in the steam generator was analyzed with paying special attention to studying their behavior in the steam generator internal cylinder. It is shown that, despite the presence of structural obstacles in the inner cylinder, coolant convective motion and bubble floatation occur. An alternative hypothesis is put forward, according to which cracks may be caused by cavitation on the secondary system coolant side. To check the hypothesis, 3D modeling was carried out, the results of which did not confirm its validity. The obtained study results can be used to substantiate measures on preventing the hydrogen-induced embrittlement of and crack formation in the steam generator piping systems of nuclear-powered icebreakers, floating nuclear power units, and small capacity NPPs.

Investigation of the hydrogen embrittlement susceptibility of steel components during thin-film hot-dip galvanizing

Abstract With regard to the application of thin-film hot-dip galvanizing to a welded steel tube structure in vehicle construction, several test series were carried out to investigate the potential for hydrogen embrittlement caused by the pretreatment media used in the galvanizing process. Here, C-ring specimens were produced from the materials E355 and C75 in different tempering states, treated in a hydrochloric acid-based operational pickle, and then tested under constant strain rate or constant load. The results show that under the investigated pickling conditions, no hydrogen-induced embrittlement effect occurs up to a hardness of 470 HV in the case of material E355 and 500 HV in the case of material C75. Only in the case of 550 HV and 600 HV, both for C75, was a tendency to embrittlement observed; this effect was more pronounced after treatment with the freshly prepared pickle than in the operating pickles. The two test methods used showed consistent results.

Ammonia mitigation and induction effects on hydrogen environment embrittlement of SCM440 low-alloy steel

The effect of ammonia (NH 3 ) contained in hydrogen (H 2 ) gas on hydrogen environment embrittlement (HEE) of SCM440 low-alloy steel was studied in association with the NH 3 concentration, loading rate, and gas pressure. NH 3 worked as both mitigator of the HEE and inducer of hydrogen embrittlement (HE) depending on the testing conditions. The mitigation of the HEE was achieved by the deactivation of the iron (Fe) surface for H 2 dissociation caused by the preferential adsorption of NH 3 on the Fe surface, which is enhanced by the increase in the NH 3 concentration and decrease in the H 2 gas pressure. NH 3 induced HE was caused due to creating hydrogen by the NH 3 decomposition. Since the NH 3 decomposition rate is low, the induction effect was observed when the loading rate was low. The effect of NH 3 was determined by the competition of the mitigation and induction effects. • NH 3 worked as both mitigator and inducer of hydrogen embrittlement. • The effects of NH 3 depended on NH 3 concentration, loading rate, and gas pressure. • NH 3 mitigated hydrogen environment embrittlement by hindering hydrogen uptake into the material. • NH 3 induced hydrogen embrittlement by creating hydrogen by its decomposition.

Effect of tempering temperature and hydrogen on deformation during tensile tests in a V-added high strength low alloy steel

Tensile behavior and hydrogen embrittlement have been investigated in a V-added high strength low alloy steel tempered at three different temperatures through slow strain-rate tensile tests and simultaneously hydrogen charging at different current densities. In the meantime, the in-situ strain field was quantitatively supervised using digital image correlation (DIC) technique. With increasing hydrogen content, the strain to fracture and work hardening exponent are greatly reduced regardless of the tempering temperature, which can indeed affect the susceptibility to hydrogen-induced embrittlement (HIE). However, in the absence of hydrogen, the steel per se displays decrement in strength, increment in ductility and slight increase in work hardening exponent with raising tempering temperature. These changes were elaborated by microstructure and a model of interaction between dislocation and hydrogen. With increasing tempering temperature, the tangled dislocation gets incompact. The hydrogen can pin the separated dislocation, but facilitate movement of the multiple dislocation. Hence the assistant force stemmed from hydrogen always increases with continuous deformation, reduces strain hardening ability, accelerates local deformation which can result in the very closely spaced dislocations being absorbed by grain boundary, then gives rise to the steel premature fracture.

Isothermal high-temperature fatigue behaviour of a near-γ titanium aluminide alloy

AbstractThe high-temperature fatigue behaviour of smooth cylindrical specimens of a near-γ-TiAl alloy with duplex microstructure was studied performing total-strain-controlled low-cycle-fatigue tests in the temperature range 500 – 750 °C. The tests were run in air and high vacuum. Mean stress, environmental degradation (oxygen- and hydrogen-induced embrittlement) and plastic strain range were identified to be the most significant parameters affecting damage evolution. The cyclic stress– strain response was found to depend strongly and characteristically on temperature. Below the brittle-to-ductile-transition temperature (TBD) of about 650 °C, cyclic deformation leads to a pronounced initial hardening manifesting itself in an increase of stress amplitude and a decrease of plastic strain range. Conversely, cyclic deformation curves from tests performed aboveTBDshow a marked state of saturation which is established already after few cycles. With increasing temperature, fatigue life decreases in vacuum. However, testing in air not only decreases fatigue life tremendously as compared to vacuum, but also leads to an inverse temperature effect, i. e., the number of cycles to failure increases with temperature.

Assessment of hydrogen embrittlement on advanced high strength steels revealed by in-situ electrochemical micro-cantilever bending test

In the current study, the hydrogen-induced embrittlement on advanced high strength steels (AHSSs) is evaluated by in-situ electrochemical microcantilever bending (IECB) tests. Microcantilevers of 1200 M and 1400 M steels were bent while hydrogen charged inside a miniaturized electrochemical cell and then compared to bent-cantilevers in the air. The results of bending experiments and post-mortem evaluation of the bent-cantilevers showed that the plastic deformation occurred for the bent-cantilevers in the air. At the same time, the reduction of yield stress and the formation of hydrogen-enhanced cracking happened for the hydrogen-charged cantilevers. The results indicated that the microcracks are initiated and propagated adjacent to the clamped boundaries of the cantilevers, where the stress intensity is topmost. This finding is demonstrated by created step-wise cracks in 1400 M representative bent cantilever. The results show that the hydrogen-enhanced dislocation nucleation and hydrogen-reduced dislocation mobility are responsible for plastic deformation and hydrogen-enhanced cracking behavior. • The effect of hydrogen on advanced high strength steels was evaluated by micro-cantilever bending tests. • Plastic deformation occurred for the bent-cantilevers in the air. • Hydrogen assisted cracking happened due to hydrogen dislocation interactions. • Cracks were initiated and propagated beside the clamped boundaries of the cantilevers.

Hydrogen embrittlement of bulk W-0.5 wt% ZrC alloy induced by annealing in hydrogen atmosphere

Annealing of a tungsten alloy containing 0.5 wt% zirconium carbide (WZC) in hydrogen atmosphere induced hydrogen embrittlement, which was investigated by exploring the evolution of the tungsten grain size and orientation, the second phase particles distribution, and the tensile properties of the hydrogen-containing and hydrogen-free WZC samples. Thermal desorption spectroscopy used to determine the hydrogen retention revealed a broad hydrogen desorption peak at 1000 – 1300 K, whose hydrogen origin was attributed to the trapping sites in the non-stoichiometric ZrCx of the WZC samples after annealing in hydrogen atmosphere at 1300 °C. Hydrogen retention resulted in the degradation of mechanical properties including strength and ductility and in the deterioration of the ductile-to-brittle-transition behavior. The results emphasize the importance of the atmosphere choice for annealing tungsten materials to avoid hydrogen embrittlement and to ensure good mechanical properties.

Effect of tempering temperature on hydrogen embrittlement in V-containing low alloy high strength steel

Three different tempering temperature were designed to investigate the effect of tempering temperature on microstructure, tensile behavior and hydrogen embrittlement sensitivity in a V-containing low alloy high strength steel. Results showed that with increasing tempering temperature, on one hand, the steel displayed decrease in strength and increase in ductility as usual, on the other hand, the susceptibility to hydrogen-induced embrittlement reduced on the same precharging hydrogen condition. These changes on properties were explained from their microstructure variation observed by X-ray diffraction (XRD) and electron backscatter diffraction (EBSD).

An Analysis of the Hydrogen Embrittlement Resistance of Aluminum Alloys

By means of quantum chemistry, it is established that tungsten and rhenium are most effective alloying elements capable of increasing the resistance of aluminum alloys to hydrogen-induced embrittlement. Tungsten (W) and rhenium (Re) atoms produce strong compression of aluminum lattice, while having sufficiently large covalent radii. In addition, each W and Re atom forms stable chemical bonds with 12 surrounding Al atoms. As a result, W and Re dopants strongly bind Al atoms, thus significantly increasing the energy of vacancy formation and suppressing the process of hydrogen-induced embrittlement. The main mechanical properties of the most hydrogen-resistant aluminum compound, WReAl24, have been calculated using the density functional theory.

Quantitative Evaluations of Hydrogen Diffusivity in V-X (X = Cr, Al, Pd) Alloy Membranes Based on Hydrogen Chemical Potential.

Vanadium (V) has higher hydrogen permeability than Pd-based alloy membranes but exhibits poor resistance to hydrogen-induced embrittlement. The alloy elements are added to reduce hydrogen solubility and prevent hydrogen-induced embrittlement. To enhance hydrogen permeability, the alloy elements which improve hydrogen diffusivity in V are more suitable. In the present study, hydrogen diffusivity in V-Cr, V-Al, and V-Pd alloy membranes was investigated in view of the hydrogen chemical potential and compared with the previously reported results of V-Fe alloy membranes. The additions of Cr and Fe to V improved the mobility of hydrogen atoms. In contrast, those of Al and Pd decreased hydrogen diffusivity. The first principle calculations revealed that the hydrogen atoms cannot occupy the first-nearest neighbor T sites (T1 sites) of Al and Pd in the V crystal lattice. These blocking effects will be a dominant contributor to decreasing hydrogen diffusivity by the additions of Al and Pd. For V-based alloy membranes, Fe and Cr are more suitable alloy elements compared with Al and Pd in view of hydrogen diffusivity.

A new perspective on hydrogen diffusion and hydrogen embrittlement in low-alloy high strength steel

Hydrogen diffusion and hydrogen induced embrittlement have been studied in low-alloyhigh strength steel tempered at three different temperature using electrochemical permeation and mechanical tensile tests, respectively. After multiple hydrogen trap sites around dislocation core was first proposed, the quantitative relations between hydrogen diffusivity, hydrogen concentration, as well as activation energy for hydrogen diffusion and hydrogen trap sites density were developed. In addition, the hydrogen-induced embrittlement would result from higher trap density and higher hydrogen concentration. Hence the connection among hydrogen diffusion, microstructure and hydrogen induced embrittlement were established where the hydrogen trap sites density served as a bridge.

The Character of Hydrogen Embrittlement in Mooring Chain Steel

The digital image correlation method has been applied to directly observe the local strain and crack formation in mooring chain steel during tensile tests in air or when simultaneously charging hydrogen in different ways, viz. including/excluding the notch root. Interestingly, hydrogen accumulation promoted crack initiation on the surface when the local strain reached approximately 0.9%, while strain of 19% to 20% was reached in the hydrogen-free specimens before visible crack formation. Even through the stress–strain curves prior to the sudden drop indicate a negligible effect of hydrogen, its presence can greatly reduce the stress-induced crack initiation. In addition, hydrogen introduced while avoiding the notch root can disorganize the regular distribution of strain produced by the notch before crack initiation. Therefore, hydrogen-induced embrittlement below the critical stress criterion can be explained by hydrogen-enhanced localized plasticity, while above the critical stress criterion, hydrogen-enhanced decohesion provides a better explanation.

Hydrogen-induced embrittlement of nickel-chromium-molybdenum containing HSLA steels

ABSTRACTSeveral advanced nickel-chromium-molybdenum high strength lowalloy steels newly developed by our research team exhibit excellent mechanical strength, toughness and hardenability. However, the phenomenon of hydrogen-induced embrittlement will easily occur for these high strength steels. In this research, the hydrogeninduced embrittlement of 8625-Modified steel (8625M steel) was studied. Experimental results show that the dominant hydrogen trapping site of the 8625M steel is dislocation, of which trapping energy is about 20 kJ/mol, indicating that the hydrogens trapped in the dislocations are diffusible. The as-quenched 8625M steel has the highest dislocation density and accordingly the highesthydrogen content after hydrogen charging. This makes the asquenched 8625M steel exhibit severe hydrogen embrittlement. After tempering at 200°C and 300°C, the dislocation density drops, and hence these tempered specimens have lower ultimate tensile strength loss. After 400°C tempering, the hydrogen embrittlement phenomenon becomes serious again, being ascribed to the formation of needlelike and film-like cementite which will weaken the strength of martensite. After 500°C tempering, the 8625M steel has the lowest dislocation density, and the inter-lath cementite become discontinuous and spheroidal, making the 500°C tempered specimen have the lowest ultimate tensile strength loss and the highest elongation after hydrogen charging in this study.