Hydrogen Embrittlement Of Steel Research Articles

Evaluating hydrogen embrittlement susceptibility of operated natural gas pipeline steel intended for hydrogen service

Green hydrogen produced by renewable energy sources is expected to play an important role as a decarbonized energy carrier. It can be transported cost-effectively over long distances by pipelines. Hydrogen transport through existing natural gas pipeline networks is supposed to be prospective. However, a possible degradation of gas pipeline steels as a result of their long-term operation should be taken into account in assessing the prospects of using the existing gas network for hydrogen transportation safely. In this study, hydrogen embrittlement susceptibility of low-carbon pipeline steel in the as-received state and after long-term operation is investigated. The influence of long-term operation on the microstructure, mechanical properties, and fracture mechanism of steel is assessed, considering the direction of cutting the specimens relative to the pipe axis. The electrolytic hydrogen pre-charging process with different intensities is used to analyze the influence of absorbed hydrogen on the mechanical behaviour of steel by tensile tests of uncharged and hydrogen-charged specimens. The as-delivered steel is not prone to hydrogen embrittlement after moderate hydrogen charging, while the operated one is sensitive to it. Metallographic and fractographic analyses revealed a crucial role of non-metallic inclusions in the hydrogen embrittlement of steel, which depended on its technical state and hydrogen charging conditions. Moderate hydrogen charging led to intergranular embrittlement of steel, while intensive − to transgranular embrittlement, indicating different mechanisms of transport of hydrogen absorbed by the metal.

Hydrogen Embrittlement as a Conspicuous Material Challenge─Comprehensive Review and Future Directions.

Hydrogen is considered a clean and efficient energy carrier crucial for shaping the net-zero future. Large-scale production, transportation, storage, and use of green hydrogen are expected to be undertaken in the coming decades. As the smallest element in the universe, however, hydrogen can adsorb on, diffuse into, and interact with many metallic materials, degrading their mechanical properties. This multifaceted phenomenon is generically categorized as hydrogen embrittlement (HE). HE is one of the most complex material problems that arises as an outcome of the intricate interplay across specific spatial and temporal scales between the mechanical driving force and the material resistance fingerprinted by the microstructures and subsequently weakened by the presence of hydrogen. Based on recent developments in the field as well as our collective understanding, this Review is devoted to treating HE as a whole and providing a constructive and systematic discussion on hydrogen entry, diffusion, trapping, hydrogen-microstructure interaction mechanisms, and consequences of HE in steels, nickel alloys, and aluminum alloys used for energy transport and storage. HE in emerging material systems, such as high entropy alloys and additively manufactured materials, is also discussed. Priority has been particularly given to these less understood aspects. Combining perspectives of materials chemistry, materials science, mechanics, and artificial intelligence, this Review aspires to present a comprehensive and impartial viewpoint on the existing knowledge and conclude with our forecasts of various paths forward meant to fuel the exploration of future research regarding hydrogen-induced material challenges.

The Role of Welding Parameters in Hydrogen Embrittlement Mitigation: A Case Study in Steel

This research investigates the mitigation of hydrogen embrittlement in steel, focusing on the effects of metallurgical hydrogen and the efficacy of various reduction techniques. Key findings demonstrate that vacuum treatment during steel casting combined with thermal treatment significantly lowers hydrogen content, enhancing steel's resistance to embrittlement. Welding processes differ in susceptibility to hydrogen-induced cracking, with submerged arc welding (SAW) showing the least and shielded metal arc welding (SMAW) the most susceptibility. Employing multipass welding, along with preheating and post-weld heat treatments, effectively minimizes hydrogen-related cracking by promoting even hydrogen distribution and desorption. The study highlights the successful application of fluoride-ion-containing welding fluxes, such as CaF2 and KF, to reduce weld hydrogen levels through chemical reactions. Furthermore, the choice of welding parameters, particularly the arc voltage, substantially impacts the hydrogen concentration in the welds. Additionally, the incorporation of hydrogen-binding elements such as yttrium significantly reduces the level of free hydrogen, thereby enhancing resistance to hydrogen corrosion. The research underlines the need for selecting appropriate welding methods and parameters to effectively reduce the adverse effects on welded joints. In conclusion, optimizing vacuum and thermal treatments, along with developing innovative welding materials, is imperative to control hydrogen content, crucial to the longevity and reliability of steel products in hydrogen-sensitive applications such as the oil and gas sector.

Hydrogen embrittlement in high strength fasteners: Comparison between bainitic and tempered martensitic steels

The scope of this work is to explore innovative microstructure typologies, as well as heat treatments, for the manufacturing of high-strength steel fasteners aimed at obtaining a reduced susceptibility to hydrogen embrittlement. The research evaluates the role of microstructure and the notch tensile strength (RNTS) in relation to the geometry tested on hydrogen embrittlement of steels used in fasteners production. High-strength steel fasteners are increasingly used especially in Automotive industry to mechanically join parts together, increase vehicle performance and promote car weight reduction. High-strength steel fasteners, included in property class 12.9 and higher, are characterized by an ultimate tensile strength above 1200 MPa, despite the remarkable mechanical performance they are historically prone to hydrogen embrittlement phenomena. The phenomenon of hydrogen embrittlement is widely investigated, characterized by its unpredictability and its ability to result in brittle fractures. In this study, slow strain rate tensile tests were conducted to investigate and compare the effect of internal hydrogen concentration on the mechanical properties of fasteners with martensitic microstructure in property classes 10.9and 12.9, as well as innovative high strength fasteners with bainitic microstructure in property class 12.9U.The commonly utilized methodologies for assessing hydrogen embrittlement in fasteners are standardized procedures primarily focused on mechanical tests conducted on finished fasteners. They do not effectively differentiate the influence of surface treatment from material selection and fastener design. For this reason, during the present research, a simpler, faster and very promising methodology has been used. This procedure could be the basis for developing a new Standard guideline for prevention of hydrogen delayed fracture. Additionally, SEM fractography has been interpreted according to the well-known HELP and HEDE models.

In-situ measurement of hydrogen entry and hydrogen embrittlement of steel by atmospheric corrosion

Hydrogen entry and hydrogen embrittlement of high-strength steel in atmospheric corrosion environment was investigated using an in-situ hydrogen permeation technique and a strain gage method, respectively. The hydrogen concentration increased at the beginning of corrosion and when the corrosion reaction was accelerated, such as when a typhoon approached. The hydrogen embrittlement occurred when the surface hydrogen concentration exceeded the critical hydrogen concentration. It is directly demonstrated that hydrogen embrittlement crack initiation, arrest, and propagation are repeated accompanied with hydrogen entry and release due to environmental changes, leading to final fracture.

A first principles study on H-atom interaction with bcc metals

Solute hydrogen trapping has long been proposed as one of the mechanisms for hydrogen embrittlement in steel. It has been reported that the maximum hydrogen trapping energy of metallic solutes ranged from −0.7 eV to −0.9 eV. In this work, the mechanism of metal-H interaction in Cr-Mo steels was investigated with first principles calculations by modelling the binary alloy Fe-X (X = C, Si, Mn, Cr, Mo) system with reference to the chemical composition of Cr-Mo steels. The formation of hydrogen bonds in the case of H atoms located at different sites in Fe-X crystals was analyzed. Results indicated that various atomic doping had different roles in hydrogen effect in the steel, with C, Si and Mo doping making the solid solution of hydrogen in Fe crystals easier, while Mn and Cr doping was rather more difficult. In Fe-Mn and Fe-Cr crystals, the repulsion between Fe lattices was insignificant when H atoms were located in tetrahedral sites, which considerably reduced the binding energy in the crystal. When H atoms were dissolved into the crystal, the interatomic bonding interactions in Fe-X crystals were weakened, resulting in higher charge density fluctuations. The current work extends the understanding of H-atom diffusion and migration in steel from the microscopic scale to the atomic and electronic scales, which underpins the physics for tailoring chemical elements of bcc metals towards higher resistance to hydrogen embrittlement.

Stiffness-based method to identify the threshold load of low hardness steels using the Incremental step loading test

Hydrogen embrittlement (HE) is one of the main problems related to the use of metallic materials in sour or wet environments. The Incremental Step-Loading (ISL) test used to evaluate the susceptibility to HE of steels has gained more visibility over recent years, thus allowing for the determination of the threshold load (Pth) in H+ enriched environments. However, the ISL standard, ASTM F1624, limits the test to steels with a minimum hardness of 33 HRC. Even for those steels with 33 HRC, the results present some misinterpretations. In addition to this fact, one needs to consider that there are several applications where steels with hardness below 33 HRC are used, as for instance, in fasteners and tool joints under cathodic protection used in the oil and gas industry, for which hardness varies from 26 to 32 HRC. In light of the aforementioned, the standard limitation represents a major disadvantage related to the application of the ISL test. Grounded upon the said, the aim of the present study is to propose a methodology based on the specimen stiffness to be used in the ISL test results, allowing the Pth determination of steels with hardness lower than 33HRC. Conventional and extended ISL tests were performed in two steels (4137-M and 4130-M) with a 32HRC hardness values. Applying the stiffness-based method on the the conventional ISL test results, a threshold load (Pth) of 71.5 %PFFS and 66.0 %PFFS were found for the 4137-M and 4130-M steels, respectively. To validate these results, extended ISL tests were performed on both steels and the results showed a Pth of 73.7 %PFFS for the 4137-M steel and 66.0 %PFFS for the 4130-M steel. The results from the conventional ISL test, using the stiffness-based method proposed in this study, provided values similar or with differences lower than 5 %PFFS, when compared alongside the extended ISL tests. Moreover, ISL tests were performed on the same steels with 40 HRC hardness, and the AISI4137-M presented a Pth of 21.6 %PFFS and for 4130-M the Pth was 22.0 %PFFS. The main conclusion obtained from these tests was that, when large amount of plastic deformation is not present on ISL test, the load drop visual detection is sufficient to determine the Pth. As expected, it was observed that both steels with 40 HRC presented higher HE susceptibility than the 32 HRC ones. This behavior was due to higher stress concentration at the notch root presented by the higher hardness condition. The stiffness-based method proved to be robust and capable of separate yielding from hydrogen induced cracking of low hardness steels and could also be used to identify the Pth values of steels with hardness lower than that specified by the ASTM F1624 standard, and which are tested using the ISL test.

Hydrogen behavior during high-temperature plastic deformation in low-alloy steels

• Interaction mechanism between thermoplastic deformation and HE. • Cross scale simulation based on MD and DFT. • Proposal and mechanism of hydrogen inhibition recovery. Hydrogen embrittlement of steel has been widely studied; however, the hydrogen behavior during thermoplastic deformation is still unknown. The hydrogen behavior in thermoplastic deformation may have a significant impact on the properties of materials after processing. In this study, hydrogen embrittlement samples were obtained using electrolytic hydrogen charging, and thermoplastic deformation experiments of hydrogen-charged samples at different temperatures were conducted. Hydrogen slightly increased the flow stress, particularly when the deformation temperature was 1123 K. Microstructure characterization revealed that the samples with a high hydrogen content had a higher dislocation density. Molecular dynamics and density functional theory calculations were performed to understand this mechanism. The difference in Gibbs free energy between systems showed that hydrogen reduced the driving force of defect recovery, making recovery more difficult. This microstructure evolution law explained the experimentally observed increase in the dislocation density due to hydrogen. The increase in dislocation density leads to an increase in the flow stress. This study provides useful information and understanding about the behavior of hydrogen during alloy processing. Improving the alloy processing method may be a powerful way to inhibit hydrogen embrittlement.

Estimation of Fatigue Crack Growth Rate in Heat-Resistant Steel by Processing of Digital Images of Fracture Surfaces

The micro- and macroscopic fatigue crack growth (FCG) rates of a wide class of structural materials were analyzed and it was concluded that both rates coincide either during high-temperature tests or at high stress intensity factor (SIF) values. Their coincidence requires a high level of cyclic deformation of the metal along the entire crack front as a necessary condition for the formation of fatigue striations (FS). Based on the analysis of digital fractographic images of the fatigue fracture surfaces, a method for the quantitative assessment of the spacing of FS has been developed. The method includes the detection of FS by binarization of the image based on the principle of local minima, rotation of the highlighted fragments of the image using the Hough transform, and the calculation of the distances between continuous lines. The method was tested on 34KhN3M steel in the initial state and after long-term operation (~3 × 105 h) in the rotor disk of a steam turbine at a thermal power plant (TPP). Good agreement was confirmed between FCG rates (both macro and microscopic, determined manually or using digital imaging techniques) at high SIF ranges and their noticeable discrepancy at low SIF ranges. Possible reasons for the discrepancy between the micro- and macroscopic FCG rates at low values of the SIF are analyzed. It has also been noted that FS is easier to detect on the fracture surface of degraded steel. Hydrogen embrittlement of steel during operation promotes secondary cracking along the FS, making them easier to detect and quantify. It is shown that the invariable value of the microscopic FCG rate at a low SIF range in the operated steel is lower than observable for the steel in the initial state. Secondary cracking of the operated steel may have contributed to the formation of a typical FS pattern along the entire crack front at a lower FCG rate than in unoperated steel.

The Potential of the Internal Friction Technique to Evaluate the Role of Vacancies and Dislocations in the Hydrogen Embrittlement of Steels

Hydrogen embrittlement of steels is known to have considerable impact in many engineering sectors. To be able to mitigate the hydrogen embrittlement problem, a profound comprehension of the interaction of hydrogen with the steel microstructure is required. Especially the interaction of hydrogen with dislocations and vacancies is very relevant as these defects are known to play an important role in hydrogen embrittlement. At present, thermal desorption spectroscopy is mostly used to study hydrogen–defect interactions. However, information obtained solely by this technique is insufficient to obtain a full understanding of the interaction of hydrogen with these defects in the steel microstructure. Herein, the use of internal friction, as a complementary technique to thermal desorption spectroscopy, to reveal the interaction of hydrogen with dislocations and vacancies, is reviewed based on the present understanding in the literature. Furthermore, the opportunities to use internal friction to characterize the interaction between hydrogen and these defects and to give more insight into the hydrogen embrittlement mechanism are discussed. It is demonstrated that internal friction has not yet been used to its full potential for this purpose, although it entails the opportunity to develop fundamental insights into the hydrogen embrittlement phenomenon.

Cycled hydrogen permeation through Armco iron – A joint experimental and modeling approach

Understanding hydrogen embrittlement in steels requires research in hydrogen diffusion and trapping at microstructural defects. The present paper deals with hydrogen permeation and trapping at defects in the base material, Armco iron, eliminating effects coupled with alloying and precipitation. Cycled permeation curves are recorded and evaluated by using sound diffusion models to identify hydrogen trap sites as dislocations, grain boundaries and vacancies and assign their trapping energies. Furthermore, trap densities are evaluated and used together with the trapping energies as parameters in an adapted diffusion equation for hydrogen, interpreting the experiments significantly better than simple use of classical Fick’s laws.

Hydrogen in Aluminium-Coated Steels Exposed to Synthetic Seawater

Thermally sprayed aluminium (TSA) coatings provide protection to offshore steel structures without the use of external cathodic protection (CP) systems. These coatings provide sacrificial protection in the same way as a galvanic anode, and thus hydrogen embrittlement (HE) becomes a major concern with the use of high strength steels. The effect of TSA on the HE of steel seems to remain largely unknown. Further, the location of hydrogen in TSA-coated steel has not been explored. To address the above knowledge gap, API 5L X80 and AISI 4137 steel coupons, with and without TSA, were prepared and the amount of hydrogen present in these steels when cathodically polarised to −1.1 V (Ag/AgCl) for 30 days in synthetic seawater was determined. One set of TSA-coated specimens was left at open circuit potential (OCP). The study indicates that the amount of hydrogen present in TSA-coated steel is ~100 times more than the amount found in uncoated steel, and that the hydrogen seems to be largely localised in the TSA layer.

Hydrogen Uptake of Duplex 2205\u202fat H2 Partial Pressures up to 100\u202fbar

Microbiological methanation is investigated in an underground natural gas reservoir. Since H2 is involved in the process, hydrogen embrittlement of steel must inevitably be considered. Therefore, a routine for testing has been developed and a unique autoclave test bench was designed to simulate field conditions. The 2205 duplex stainless steel (UNS S31803) was investigated. Constant load tests (CLTs) and immersion tests with subsequent hydrogen analyses were performed. The specimens were exposed to different partial pressures of H2 under both dry and wet conditions (with brine). Additionally, the influence of CO2 under wet conditions was covered. Tests were performed at two different temperatures (25 °C and 80 °C) and lasted for 30 days. In general, the duplex stainless steel shows a good resistance to hydrogen embrittlement, but a significantly higher hydrogen uptake was obtained compared to other steel grades.

Study of the Protective Efficiency of Bactericides Against Steel Corrosion in Low-Mineralized Sulfide-Containing Environments with Different pH Values

In this work, the effectiveness of three industrial bactericides and urotropine in inhibiting corrosion and hydrogen embrittlement of steels in 0.5% NaCl solution at different H2S concentrations and pH values was investigated. The capability of the studied substances for chemical inactivation of hydrogen sulfide was also experimentally evaluated. It has been shown that bactericides effectively inhibit corrosion only if at least 50 mg/L of H2S are presented in the medium.

The effect of hydrogen concentration on the fracture surface of medium Mn steels

To balance good strength and ductility, Medium Mn steels have been considered as the new generation materials used in automotives. However, they show delayed fracture, which is thought to relate to hydrogen. Therefore, in order to understand their mechanical properties with various hydrogen contents, it is very important to assess their safety. In this study, the effect of hydrogen on the mechanical properties of several medium Mn steels (MMSs) with different Mn content and treatments were investigated. For medium Mn steels, the stability of the retained austenite (RA) was examined and the hydrogen permeation test was performed. Austenite, as a barrier to hydrogen diffusion, leads to a tortuous diffusion path, which reduces the diffusion rate of hydrogen in MMSs. Increasing the Mn content increases the volume fraction of RA in the specimen. The stress-strain curves of MMSs were divided into three parts, determined by the stability and content of RA. Slow strain rate tensile tests with hydrogen charging were performed to investigate the behaviour of hydrogen diffusion and the mechanism of hydrogen embrittlement (HE). After the tests, the hydrogen content was measured and the fracture surface was observed and analysed. The phenomenon of HE in steels has been mainly explained based on the mechanisms of hydrogen-enhanced localised plasticity (HELP), hydrogen-enhanced decohesion (HEDE), and hydrogen assisted micro ovoid coalescence (HDMC). Due to the existence of hydrogen, fracture morphology changes from ductile mode to brittle mode. It was also found that under the same strain rate, tensile strength and elongation decrease gradually as hydrogen concentration increases, resulting in final failure.

A fully coupled implementation of hydrogen embrittlement in FE analysis

Proper understanding of hydrogen embrittlement in steel is of paramount importance in several engineering applications, e.g. oil & gas and hydrogen storage & transport.This phenomenon can be modelled by means of a mass diffusion analysis driven by mechanical fields, i.e. hydrostatic stress gradient and plastic strain. Since the mechanical response depends on the hydrogen content itself, continuum mechanics and mass diffusion equations are fully coupled.Accordingly in this paper a fully coupled–cohesive zone implementation is presented for the Abaqus Finite Element code, adopting the coupled thermal–stress analysis and the analogy between mass diffusion and heat transfer. The implementation requires extensive use of FORTRAN user subroutines and common blocks to share data, plus some auxiliary Python scripts.With the aim to provide a practical example to the use of the code, a FE model reproducing a fracture toughness test of C(T) specimen charged with atomic hydrogen is described. Moreover, a sensitivity analysis of the model shows the capability of the developed numerical tool in predicting hydrogen embrittlement.The code developed in this paper is open source under a permissive free software license.

Hydrogen permeation barriers: Basic requirements, materials selection, deposition methods, and quality evaluation

Abstract An effective permeation reduction of gaseous hydrogen isotopes into a metal wall by introducing a barrier is essential in two main fields: prevention of hydrogen-embrittlement in steels and control of the tritium inventory in future nuclear fusion reactors. By far the most important advances and relevant studies originate from the Nuclear Fusion Community where tritium retention is an important issue, influencing safety issues. Stable permeation barriers are searched among materials with the lowest bulk hydrogen solubility and diffusivity. Besides a few specific pure metals, like beryllium and tungsten, dense oxides, nitrides and carbides have been mostly investigated. Coating techniques for preparation of well adhered and perfect barriers are evidently of the same importance as the material selection itself. Most attractive are the techniques where an ad-layer is formed simply by oxidation. Other methods require specific gas environments with strong electric and magnetic fields, which may represent a limit for the ad-layers uniform coverage over large and uneven areas. Evaluation of the achieved barrier performances is another challenging task. Several new methods, which can trace hydrogen isotopes in bulk at very low concentrations, often miss in the determination of their mobility. Also, they do not reveal the role of barrier defects. The classical gas permeation rate method through coated membranes is still the most reliable option to determine the actual Hydrogen Permeation Barrier (HPB) efficiency. At elevated temperature, the hydrogen permeation rate is recorded at the downstream side of a coated membrane exposed to a substantially higher hydrogen upstream pressure. By using modern vacuum instrumentation techniques, even the most effective barriers can be well characterised.

Numerical analysis of hydrogen transport into a steel after shot peening

Abstract Surface peening is a potential method of suppressing hydrogen embrittlement (HE). But experimental observations in literatures have shown that it can suppress HE of steels exposed to a mild hydrogen-containing environment, but in a severe hydrogen-containing environment it enhances HE. To explain this from the perspective of hydrogen transport and concentration, this paper gives a numerical analysis of hydrogen transport into a PSB1080 high strength steel after shot peening (SP) focusing on the combined effect of residual compressive stress and SP plastic deformation on diffusion. The diffusion model established by Oriani and Sofronis et al. is used, which considers the effect of the increase of trap sites due to plastic strain and assumes that the populations of hydrogen in trap sites and in normal lattice sites are in equilibrium. The results were related to experimental observations. In mild hydrogen-containing environment, the increase of trap sites due to SP can significantly reduce the apparent hydrogen diffusivity, thus suppress the transport and resulting hydrogen concentration level in normal lattice sites. As a result, hydrogen trapped at grain boundaries is reduced, and HE mechanism changes from HEDE to simultaneous HELP and HEDE. Intergranular fracture is suppressed thus reducing HE. And the suppression of hydrogen transport increases with increasing shot velocity, as a faster shot gives rise to more severe plastic deformation. In severe hydrogen-containing environment, SP deformation has little influence on diffusivity but significantly increases trapped hydrogen, leading to irreversible hydrogen blisters hence enhancing HE.

Electrochemical fracture analysis of in-service natural gas pipeline steels

Long-term operation of natural gas transit pipelines implies aging, hydrogen-induced and stress corrosion cracking and it causes hydrogen embrittlement of steels, degradation of mechanical properties associated to a safe serviceability of pipelines, and failure risk increase. The implementation of effective diagnostic measures of pipelines steels degradation would allow planning actions in order to reduce a risk of fracture. In this paper, a new scientific and methodical approach based on the electrochemical analysis of fracture surface for evaluation of in-service degradation of operated pipeline steels was developed. It was suggested that carbon diffusion to grain boundaries and to defects inside grains, intensified by hydrogen, under long-term operation led to formation of nanoparticles of carbides, which resulted in intergranular cracking of operated pipeline steels under service and their transgranular cracking under impact toughness testing. Therefore, fracture surface was enriched by carbon compounds, and electrochemical characteristics were sensitive to this. In-service degradation of ferrite-pearlite pipeline steels was accompanied by a sharp shift in open-circuit potential of the fracture surface (brittle fracture) of specimens after impact toughness tests compared with that of polished steel surfaces. A significant difference between potentials of the fracture surface and the polished steel surface (over 60 mV in 0.3% NaCl solution) of specimens made of ferrite-pearlite pipeline steels observed after their long-term operation was evidently due to the increased content of carbon compounds on the fracture surface. Mechanism of ferrite-pearlite pipeline steels embrittlement under operation consisted in carbides enrichment not only grain boundaries, but also intragranular defects, has been revealed, as it is indicated by an increase of carbon content on transgranular fracture surfaces determined electrochemically.

Novel Methods for Prevention of Hydrogen Embrittlement in Iron

Iron is the most widely used metal in the world. However, hydrogen embrittlement in steels—iron based alloys—is an important issue related to the safety of our infrastructure, such as railroads and bridges. Therefore, the prevention of hydrogen embrittlement in steels is necessary. In the present study, we demonstrate two novel methods for the prevention of hydrogen embrittlement in iron: one involves the low-energy implantation of helium, which is usually an element harmful to metals, into iron, the other is inducing damage to the iron surface by ion irradiation. In general, irradiation with high-energy particles leads to metal brittleness. In the former method, the driving force for hydrogen embrittlement in iron is weakened, in the latter method, hydrogen diffusion in iron is prevented because of trapping of hydrogen atoms in the vacancies produced by the irradiation. As a result, hydrogen embrittlement in iron was suppressed by both methods.