Electrochemical Hydrogen Charging Research Articles

Effects of grain boundary character distribution on hydrogen-induced cracks initiation and propagation at different strain rates in a nickel-saving and high-nitrogen austenitic stainless steel

The effect of grain boundary character distribution (GBCD) on hydrogen-induced cracks (HICs) initiation and propagation in nickel-saving austenitic stainless steel was investigated at different strain rates with electrochemical hydrogen charging. The fracture strength and elongation of specimens decreased as the strain rates decreased due to more hydrogen atoms being transported by mobile dislocations. HICs are more likely to initiate at random grain boundaries (RGBs) because of poor deformation coordination of adjacent grains at RGBs after hydrogen charging. Special boundaries (SBs) deflected HICs and hindered the propagation of HICs owing to a more stable boundary structure and less strain localization during slow strain rate tensile (SSRT) deformation with hydrogen charging. Furthermore, highly efficient distributions of SBs contribute to great resistance to hydrogen embrittlement.

Effect of coating on hydrogen embrittlement of hot stamping 22MnB5 high strength steel during electrochemical charging

This study investigated the effect of Al–Si coating and its service condition on hydrogen embrittlement (HE) of hot-stamped ultra-high strength martensitic steels (22MnB5) through electrochemical hydrogen charging. The HE behaviour of coated and uncoated specimens under different charging conditions was investigated. The deterioration degree of mechanical properties of charged specimens with charging current is monotonous. At low-current charging, the more severe deterioration of coated specimens due to the excess hydrogen which was provided by corroded coatings. Contrary, with high-current charging, the integral coatings provided effective protection and retarded HE behaviour. Furthermore, the scanning electron microscopy revealed a similar transition of fractography, i.e., from ductile (uncharged) to quasi-cleavage (0.001A-2h) and a mixture of quasi-cleavage and intergranular fracture (0.1A-2h). Additionally, the coated tailor rolled blank steel was selected to investigate the effect of coating condition on HE. It revealed that the deformation-induced defects on coatings would impair the resistance to HE. Thus, we demonstrated that the Al–Si coating which effectively alleviate HE, was dependent on its integrality.

Correlation between grain size variation and hydrogen embrittlement in a cost-effective Fe40Mn40Ni10Cr10 austenitic medium entropy alloy

The effect of grain size variation (11 μm, 34 μm) on the hydrogen-induced tensile properties degradation of a Co-free cost-effective Fe40Mn40Ni10Cr10 austenitic medium entropy alloy was investigated using a slow strain rate test. Despite improving both strength and ductility with decreasing the grain size in non-charged conditions, the fine-grain alloy showed a higher relative elongation loss after electro-chemical hydrogen charging. The larger ductility loss in the fine-grain alloy was ascribed to the fast propagation rate of major intergranular cracks and the drastic strain hardening rate drop of the alloy under hydrogen charging. The Schmid factor analysis showed that the enhanced dislocation activity in the fine-grain alloy compared with coarse-grain one was responsible for rapid hydrogen transfer to the grain boundaries, fast dislocation pile-up behind the grain boundaries, and, consequently, more severe hydrogen embrittlement. The significant stress concentration near the grain boundaries and fast intergranular crack propagation were recognized to be the main reason for premature fracture in fine-grain alloy.

Effect of hydrogen traps on hydrogen permeation in X80 pipeline steel —— a joint experimental and modelling study

The permeation of hydrogen in the X80 steel was studied in this paper through thermal desorption spectroscopy, stepwise hydrogen permeation experiments and finite element modelling. Firstly, one kind of shallow trap and deep traps in X80 steel were identified through thermal desorption spectroscopy and the corresponding binding energies were obtained. According to the experiment and simulation, the deep hydrogen traps can significantly retard the first hydrogen permeation process but have almost no effect during the following charging. The X80 steel used in hydrogen compressed natural gas pipelines is exposed to hydrogen for long periods and deep traps are filled, its hydrogen permeation process is more in line with the stepwise hydrogen charging. Therefore, the stepwise hydrogen charging experiments were performed and the apparent diffusion coefficients (Dapp) and the hydrogen trap density involved in the hydrogen permeation transient (N1) were obtained using three different thickness samples. Then, a quantitative relationship in X80 steel was fitted between the N1 and the variation of hydrogen concentration. Based on the quantitative relationship and the hydrogen trap binding energies, a hydrogen permeation model in X80 steel was established. By comparing the hydrogen permeation curves obtained by our model under different boundary conditions with experiment curves, it is found that the constant concentration boundary condition model can better describe the hydrogen permeation kinetic in X80 steel under electrochemical hydrogen charging. As a result, this model can be used to predict the distribution of hydrogen in X80 steel, laying the foundation for predicting the occurrence of hydrogen embrittlement in pipeline steels.

The Effect of Strain Rate on the Hydrogen Embrittlement Susceptibility of Aluminum 7075

Abstract The effects of changing the strain rate regime from quasi-static to medium on hydrogen susceptibility of aluminum (Al) 7075 were investigated using tensile tests. Strain rates were selected as 1 s−1 and 10−3 s−1 and tensile tests were conducted on both hydrogen uncharged and hydrogen charged specimens at room temperature. Electrochemical hydrogen charging method was utilized and the diffusion length of hydrogen inside Al 7075 was modeled. Material characterizations were carried out by X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) and microstructural observations of hydrogen uncharged and hydrogen charged specimens were performed by scanning electron microscope (SEM). As opposed to earlier studies, hydrogen embrittlement (HE) was more pronounced at high strain rate cases. Moreover, hydrogen enhanced localized plasticity (HELP) was the more dominant hydrogen embrittlement mechanism at slower strain rate but coexistence of hydrogen enhanced localized plasticity and hydrogen enhanced decohesion was observed at a medium strain rate. Overall, the current findings shed light on the complicated hydrogen embrittlement behavior of Al 7075 and constitute an efficient guideline for the usage of Al 7075 that can be subject to different strain rate loadings in service.

Metallic Material Evaluation of Liquid Hydrogen Storage Tank for Marine Application Using a Tensile Cryostat for 20 K and Electrochemical Cell

A series of material tests were performed on cryogenic metallic materials meant for liquid hydrogen storage tanks using a 20 K tensile cryostat and an electrochemical hydrogen-charging apparatus. Mechanical evaluation of the electrochemically hydrogen-charged specimens was performed in a tensile cryostat using helium gas at ambient temperature and cryogenic temperature (20 K). The tensile cryostat was equipped with a vacuum jacket and a G-M cryocooler with gaseous helium. Furthermore, the cathodic electrolysis cell used for charging the specimens was adopted for internal hydrogen conditions with a reflux condenser and heating mantle to increase hydrogen diffusivity. The target materials were austenite stainless steel and aluminum alloy, which are suitable for liquefied natural gas and gaseous hydrogen environments. No significant change in the yield strength and flow stress of the hydrogen-charged specimen up to 20% strain was observed. However, changes in tensile strength and elongation were observed thereafter. Electrochemical hydrogen charging of stainless steel leads to a high concentration of hydrogen on the surface of the specimen. The resulting surface cracks reduced the flow stress. The 20 K tensile test showed discontinuous yielding in the austenitic stainless steel with an abrupt increase in temperature. The mechanical performance of the aluminum alloys improved in terms of strength and elongation. Changes in the mechanical performance and relative area reduction were observed for all the metallic materials at 300 K and 20 K.

Detection of voids in hydrogen embrittled iron using transmission X-ray microscopy

Hydrogen embrittlement remains a barrier to widespread adoption of hydrogen as a carbon-neutral energy source. Here, hydrogen embrittlement mechanisms are investigated across length scales in iron using transmission X-ray microscopy (TXM), digital image correlation (DIC), and notched tensile testing during in-situ electrochemical hydrogen charging. TXM reveals void size and spatial distribution ahead of a propagating crack. We find hydrogen charging leads to voids within ∼10 μm of the crack tip and suppression of voids beyond this distance. Near the crack tip, voids are elongated in the direction of the crack and are smaller than voids in an uncharged sample. In the presence of hydrogen, these voids lead to quasi-cleavage fracture and a sharper crack tip. DIC shows localization and reduction of plastic strain with hydrogen charging, and tensile testing reveals a reduction in fracture energy and elongation at failure. These results are discussed in the context of hydrogen embrittlement mechanisms.

Effect of Hydrogen on Corrosion Behavior of 321 Stainless Steel in NH4Cl Solution.

For a hydrogenation heat exchanger operating under severe working conditions such as high temperature, high pressure and a hydrogen environment, perforation accidents caused by NH4Cl corrosion occur frequently. However, few reports on the effect of hydrogen on the corrosion behavior of metal materials in NH4Cl aqueous solution have been published. In this paper, X-ray photoelectron spectroscopy (XPS), electrochemical dynamic potential polarization, electrochemical impedance spectroscopy (EIS), Mott–Schottky (M-S) curves and scanning electron microscopy (SEM) were used to study the effect of electrochemical hydrogen charging (EHC) on the corrosion behavior of 321 stainless steel in an NH4Cl solution environment. The results show that: (1) hydrogen can change the structure and chemical composition of 321 stainless steel passive film and promote the conversion of metal oxide to hydroxide. At the same time, it can reduce the stability of the passive film. (2) Hydrogen can increase the thermodynamic and kinetic tendency of corrosion reaction and cooperate with Cl− to promote the occurrence of pitting corrosion.

Hydrogen Embrittlement Behavior of Plastically Pre-Strained and Cathodically Hydrogen-Charged 316H Grade Austenitic Stainless Steel

In this work, the effects of electrochemical hydrogen charging of 316H grade austenitic stainless steel were investigated in order to characterize its hydrogen embrittlement (HE) resistance. The as-received 316H material was in a fully recrystallized (solution-annealed) material condition. The susceptibility to HE of the studied material was evaluated by determination of the embrittlement index from the results of conventional uniaxial tensile tests of nonhydrogenated and hydrogen-charged test specimens. The study was focused on the effects of two selected plastic pre-strain levels of tensile specimens on their resulting HE resistance. The selected pre-strains corresponded to the tensile stress conditions within the “yield stress–ultimate tensile strength” (YS–UTS) range and directly at the UTS point. The obtained embrittlement indices for the presently used pre-straining and hydrogen charging conditions indicated that the HE of the studied material states was small. However, it was revealed that the observed degradation of deformation properties of plastically pre-strained and hydrogen-charged materials was mainly caused by gradual plasticity exhaustion due to tensile straining, which well correlated with the observed effects indicated by electron backscatter diffraction analyses and indentation hardness measurements.

Resistance of Quench and Partitioned Steels Against Hydrogen Embrittlement

Multiphase ultra-high strength steels (UHSS) containing retained austenite (RA) appear to be among the most interesting steels for the automotive industry. Developments in the last decades have allowed obtaining a very good combination of mechanical strength and ductility. Quenching and partitioning (Q&P) steels have been proposed as third-generation UHSS, reaching ultimate tensile strength up to 1300 MPa along with excellent fracture elongations of more than 15%. However, the use of Q&P steels is mainly limited by their susceptibility to hydrogen embrittlement (HE). The present work investigates the influence of the Q&P heat treatment parameters on the mechanical properties and on the HE resistivity of 20Mn-Si wire rod steel. The HE resistivity was measured using incremental step load testing with in situ electrochemical hydrogen charging according to ASTM F1624-12 standard. A comprehensive microstructure characterization was performed to examine volume fraction, nucleation sites and morphologies of RA. Although the mechanical properties were similar after Q&P heat treatment, an increase in the partitioning time revealed a significant increase in the HE threshold stress of more than 200 MPa.

Investigation of the hydrogen-induced cracking of E690 steel welded joint in simulated seawater

Hydrogen-induced cracking (HIC) behavior and mechanism of E690 welded joint in simulated seawater were studied via microstructure observations, electrochemical hydrogen charging, slow strain rate tension (SSRT) tests and hydrogen content measurement. The results show that the welded joint of E690 steel has a higher HIC susceptibility than that of base metal, in which the inter-critical heat affected zone (ICHAZ) is composed of polygonal ferrite and granular bainite is the final fracture location in the joint. ICHAZ with the lowest yield strength deformed preferentially under the tensile stress, and subsequently, the proliferating dislocations with the deformation strengthening and the continuously charged hydrogen led to the HIC and brittle fracture at the ICHAZ of the welded joint. Moreover, the HIC susceptibility was linearly dependent on the logarithm of total hydrogen concentration in the steel, and the hydrogen concentration had a more obvious effect on the welded joint than the base metal. The higher density of piled dislocations adjoining the M/A islands in the welded joint exhibited a significant effect on the hydrogen agglomeration and diffusion, which enhanced the HIC susceptibility.

Investigation of hydrogen embrittlement properties of Ni-based alloy 718 fabricated via laser powder bed fusion

The hydrogen embrittlement behavior of heat-treated Alloy 718 fabricated by laser powder bed fusion was fundamentally investigated under electrochemical hydrogen charging. The H transitioned the fracture mode from ductile dimpled to transgranular fracture with a flat fracture surface. Crystallographic analysis showed that H promoted the dislocation slip band, and the resulting concentrated strain and H along the slip planes caused cracking regardless of the distribution of additive manufacturing (AM) microstructural features such as sub-grain boundaries. In addition, thermal desorption spectroscopy and H-permeation tests indicated that the AM microstructural features after heat treatment only slightly influenced the H trapping and diffusion.

Evaluation of hydrogen embrittlement by the scratch method

PurposeThe purpose of this paper is to find a new method to evaluate the hydrogen embrittlement performance of heterogeneous materials and thin film materials.Design/methodology/approachThe changes of hydrogen embrittlement properties of steel were studied by electrochemical hydrogen charging test and scratch test. The microstructure and properties of the alloy were analyzed by hardness tester, scanning electron microscope and three-dimensional morphology. The fracture toughness before and after hydrogen charging was calculated based on the scratch method.FindingsThe results showed that the hydrogen-induced hardening phenomenon occurs in the material after hydrogen charging. The scratch depth and width increased after hydrogen charging. The fracture toughness obtained by the scratch method showed that hydrogen reduces the fracture toughness of the material. The comparison error of fracture toughness calculated by indentation method was less than 5%.Originality/valueThe results show that the scratch method can evaluate the hydrogen embrittlement performance of the material. This method provides a possibility to evaluate the hydrogen embrittlement of thin-film and heterogeneous materials.

Research on the hydrogen assisted fatigue damage in X80 pipeline steel welded joint

This paper aims to investigate the mechanisms of HIC and HAFC in X80 pipeline steel welded joints through fatigue experiments conducted on the smooth fatigue specimens after a treatment of electrochemical hydrogen charging. The characterization of propagation paths of HIC and HAFC was carried out by OM and EBSD techniques. Mathematical and physical models for fatigue life and diffusible hydrogen concentration were established in X80 pipeline steel welded joint and results showed that the saturation concentration of diffusible hydrogen in X80 pipeline steel welded joint is refined to (19−20) × 10−6 mol/cm3, both HICs and HAFCs are preferentially propagated through fusion line of heat affect zone for the large variety in grain boundary and low KAM values. In addition, MnO inclusions introduced in welding process play an important role in turning away of HAFCs propagation direction despite of the straightforward HICs.

Feasibility of using ultrasonic-based prediction for hydrogen embrittlement susceptibility of high-strength heat-resistant steel 2.25Cr-1Mo-0.25V

Nondestructive evaluation for the mechanical properties loss of equipment materials serviced in the hydrogen environment is particularly vital for monitoring the equipment operating conditions. In this study, the quantitative relationship between the introduced hydrogen content and the mechanical property degradation of 2.25Cr-1Mo-0.25V steel was investigated using electrochemical hydrogen charging technique and tensile testing, and a nondestructive testing method based on pulse-echo ultrasonic measurement technique, combined with the results of mechanical assessment for hydrogen embrittlement (HE) susceptibility, was proposed to indirectly estimate the degree of hydrogen-induced plasticity loss of the steel. Moreover, signal reconstruction technique was also used to improve the measurement accuracy of ultrasonic echo signal. The results of the study showed that hydrogen present in the metal lattice intensifies the energy attenuation of ultrasonic echo, verifying the feasibility and validity of the measurement method in the effective online prediction of HE susceptibility of the tested steel.

Coupling effects of hydrogen and Dy/Nb on magnetic properties of sintered NdFeB magnets

The magnetic-property changes in sintered NdFeB magnets with different content of Dy and Nb after electrochemical hydrogen charging (EHC) were investigated. The phases of Dy2Fe14B, NbFeB, and Fe2Nb are confirmed by energy-dispersive spectrometry (EDS) and selected area electron diffraction. The electron back-scatter diffraction (EBSD) and electrochemical test show that the amount of Nd-rich grain boundary phases as hydrogen diffusion channels and the concentration of hydrogen near the surface of the magnets increase with the addition of Dy and Nb. Before and after EHC, the surface roughness and magnetic properties were measured using a laser scanning confocal microscopy, pulsed field magnetometer and flux meter. The results revealed that the surface roughness of magnets increases, owing to the absorption of hydrogen. During EHC, the remanence (Br) remains unchanged, whereas the magnitudes of the coercivity, magnetic moment (Mt), and maximum energy density ((BH)max) decrease by different degrees because of the presence of Dy and Nb compounds. Hydrogen decreases the stability of the magnet in demagnetization field by reducing the critical energy required for magnetic moment rotation, nucleation of reverse domains, and expansion of domain walls, and the presence of Dy and Nb compounds exacerbates the stability.

Study on the Effect of Microstructure Gradients Caused by Heat Gradients on Hydrogen Embrittlement Sensitivity in Heavy Forgings

The hydrogen embrittlement problem of alloy steel heavy forgings not only has the common properties of general hydrogen embrittlement, but also has the characteristics brought by its scale characteristics. The research of hydrogen embrittlement, combined with its characteristics and commonness, is of vital importance for the service safety of engineering structures. The temperature field and microstructure distribution in the machining process were investigated through the simulation of a finite element. On this basis, the physical simulation experiments were carried out to obtain the microstructure of heavy forgings in radial directions. The hydrogen embrittlement sensitivity was characterized by electrochemical hydrogen charging and slow strain rate tests (SSRT). The microstructure and fracture morphology of the samples were characterized to explore the law and mechanism of hydrogen embrittlement sensitivity gradient distribution along the axial direction. It is helpful to understand the hydrogen embrittlement of heavy forgings in order to guide engineering practice.

Influence of electrochemical hydrogenation parameters on microstructures prone to hydrogen-induced cracking

When pipeline steels are exposed to hydrogen-rich environments during service, this can lead to a degradation in mechanical properties and premature failure. These steels are often susceptible to hydrogen embrittlement and hydrogen-induced cracking (HIC) and contain very sensitive microstructures for HIC formation. This work aims to find a suitable hydrogenation methodology that allows to charge pipeline steel specimens without inducing any hydrogen related damage during the charging process. Therefore, different electrochemical hydrogen charging methodologies are evaluated. The susceptibility to HIC and blisters of two pipeline steels (API 5L grades X70 and X56), is first investigated in a sulfuric acid electrolyte. Both grades are prone to HIC in the mid-thickness section of the pipeline wall. For X56, significant blistering occurs as well, and hydrogen-induced damage could be linked to elongated MnS inclusions. For the X70 steel, hard bands are found to be vulnerable to HIC. The electrochemical charging conditions are modified for the X56 steel, where the extent of the damage is greatest due to its prone microstructure, as revealed by scanning electron microscopy. Lowering the sulfuric acid concentration and applied charging current density does lead to some reduction of blistering. However, changing to a different, sodium hydroxide-based electrolyte is more effective in mitigating the extent of the hydrogen-induced damage and the time at which it appears.

Effects of hydrogen and load frequency on the fatigue crack propagation behavior of selective laser melted Inconel 718 alloy

Hydrogen-assisted fatigue crack propagation behavior of a selective laser melted Inconel 718 alloy was investigated under in situ electrochemical hydrogen charging, and by multi-scale microstructural analysis. Results show that hydrogen significantly accelerates fatigue crack growth rate (FCGR), and such effect is intensified when decreasing load frequency. Crack propagation along cellular structure boundaries and decrease of plasticity along the crack have been evidenced. Hydrogen decreases the critical strain for crack propagation and results in the acceleration of FCGR. Lower load frequency induces higher amplitude of concentration fluctuation and larger penetration depth of hydrogen ahead of the crack tip, thus further promotes the acceleration of FCGR.

Effect of electrochemical hydrogen charging on the mechanical property and corrosion behavior of Ti-3Mo alloy

The effect of electrochemical hydrogen charging on the mechanical property and corrosion behavior of Ti-3Mo alloy was investigated. Failure analysis revealed that the crack initiation and propagation were not along the crack tip of HICs although the existence of preferential cracking in α phase. The crack tended to propagate along the α/β interface rather than directly through α phase. Besides, icorr and ip increased with an increase in charging time from 0 h to 96 h, suggesting that hydrogen charging deteriorated the corrosion resistance of the matrix, which was attributed to the redox transformation process of the passive film.