Hydrogen Gas Environment Research Articles

Effect of Hydrogen Exposure on the Notch Tensile Properties of High Strength Steel in Hydrogen Gas Environment

The effect of hydrogen exposure on high strength steel, SCM435, based on a sharp notched specimen was investigated. Tensile tests were carried out in hydrogen gas and helium gas environments. In the hydrogen gas environment, specimens that were not exposed to hydrogen gas and specimens that were exposed to hydrogen gas for 48 h were used. As the result of the tensile tests with specimens of various notch depths, the tensile strengths of the hydrogen-gas-exposed specimens were higher than that of the non-exposed specimens. The tensile strength increases with the exposure time in hydrogen gas until hydrogen homogeneously diffuses in the entire specimen for the notched specimens of t =1.0 mm. The fracture surfaces of the specimens in hydrogen gas showed an intergranular fracture near the notch root while the specimens in helium gas showed a fracture mode of microvoid coalescence. The crack initiation stress of the non-exposed specimen was lower than that of the 48h-hydrogen-exposed specimen.

Effects of Mechanical and Environmental Factors on the Notch Tensile Strength of 1,300MPa Class SCM435 High-Strength Steel in Hydrogen Gas

There are several factors that affect the strength of high-strength steel SCM435 as a sharp notched specimen in a hydrogen gas environment. In this paper, tensile tests were carried out in several hydrogen and helium gas environments. The examined factors were the gas pressure, the gas temperature, the cross-head speed and the notch root radius. The results of the tensile tests in the hydrogen gas environments showed a decrease in the tensile strengths for any given environmental factor. This was not observed in the helium gas environments. Additionally, by investigating the area of intergranular fracture, it was found that the tensile strength had a reciprocal relationship with the area of the intergranular fracture regardless of several environmental factors.

Hydrogen Concentration Estimation Based on Density Functional Theory in Aluminum and Alpha Iron under Gaseous Hydrogen Environments

Hydrogen Concentration Estimation Based on Density Functional Theory in Aluminum and Alpha Iron under Gaseous Hydrogen Environments

Development of EAM Potential for Fe with Pseudo-Hydrogen Effects and Molecular Dynamics Simulation of Hydrogen Embrittlement

Numerous studies have reported that solute hydrogen atoms and lattice defects have strong interactions, and that hydrogen atoms significantly change the stability and/or mobility of lattice defects. Although molecular dynamics (MD) simulations can treat complicated interactions of various lattice defects, the time scale is insufficient to treat hydrogen diffusion so as to influence the lattice-defect generation and cooperative motion of hydrogen atoms and lattice defects. Here we developed an interatomic potential for Fe with pseudo-hydrogen effects on lattice-defect energies and performed MD simulations of tensile loading. First, we estimated the lattice-defect energies of Fe and hydrogen-trap energies of lattice defects by using first-principle calculations and evaluated the lattice-defect energies under a practical gaseous hydrogen environment. Second, we refitted the existing embedded-atom-method potential for Fe to represent the lattice-defect energies amended by hydrogen effects. Finally, we confirmed that our potential is applicable for various phenomena by estimating the reproducibility of grain-boundary energies that are not employed for potential fitting. Our tensile-loading simulations of a nano specimen show that hydrogen reduces elongation at rupture.

1009 第一原理計算を用いた化学ポテンシャル評価に基づく水素ガス環境における金属への固溶水素濃度の評価(OS9,OS10 合同ポスターセッション,OS・一般セッション講演)

1009 第一原理計算を用いた化学ポテンシャル評価に基づく水素ガス環境における金属への固溶水素濃度の評価(OS9,OS10 合同ポスターセッション,OS・一般セッション講演)

Hydrogen Embrittlement Properties of Stainless and Low Alloy Steels in High Pressure Gaseous Hydrogen Environment

Recent research on Hydrogen Environment Embrittlement (HEE) susceptibility of stainless and low alloy steels in highly pressurized gaseous hydrogen environments was reviewed from the viewpoint of tensile properties, hydrogen absorption and fatigue properties.HEE susceptibility evaluated by Slow Strain Rate Test (SSRT) in high pressure hydrogen environments strongly depended on steel chemical compositions. Austenitic stainless steels such as type 316L or iron-based superalloy as A286 showed sufficient resistance to HEE, while stainless steels with low levels of alloying elements such as type 304L showed a remarkable ductility loss in high pressure gaseous hydrogen due to martensitic transformation. Martensitic stainless or low alloy steels also showed a remarkable ductility loss in gaseous hydrogen.Relationship between HEE susceptibility and an amount of hydrogen absorption was investigated. HEE susceptibility and hydrogen embrittlement under cathodic charging in aqueous solution showed the same dependence on the amount of hydrogen absorption, which implies HEE occurs by hydrogen absorption from external gaseous hydrogen environments.Fatigue properties in high pressure gaseous hydrogen environments were evaluated by means of internal or external pressurization tests. Austenitic stainless steels such as type 316L showed little decrease in fatigue life by hydrogen, while metastable stainless steel as type 304 or precipitation hardened superalloy as A286 showed degradation in fatigue life by hydrogen gas. Low alloy steel also showed a decrease in fatigue life in hydrogen, while high strength low alloy steel with much Mo and V showed longer fatigue life than conventional steel.

Hydrogen–Grain Boundary Interaction in Fe, Fe–C, and Fe–N Systems

Highly accurate predictions of hydrogen’s influence on material strength and development of materials with minimal hydrogen effects are essential to prevent failure under various hydrogen environments. Here, we investigated the influence of misorientation angle and solute elements (carbon and nitrogen) on the cohesive energy of symmetrical tilt grain boundaries (STGBs) in bcc Fe under a gaseous hydrogen environment by using density functional theory. We found a good correlation among GB energy, GB free volume, and the hydrogen concentration at GBs under hydrogen environments: high-energy GBs have large gaps, and many hydrogen atoms are captured at these spaces. Thus, higher-energy GBs are more influenced by hydrogen. It is also shown that the binding energy between hydrogen and a GB is negligible when nitrogen or carbon atoms exist at the GB at their solubility limit. Therefore, carbon and nitrogen atoms exclude hydrogen atoms from GBs and improve the cohesive energy of GBs under hydrogen environments.

On the environmental similitude for fracture in the SENT specimen and a cracked hydrogen gas pipeline

We investigate the use of laboratory fracture specimens to ascertain the resistance to hydrogen embrittlement of a hydrogen pipeline with an axial crack on the inner diameter (ID) surface. In particular, we study the interaction of hydrogen with material elastoplasticity in single edge notch tension (SENT) specimens loaded in hydrogen gas at a pressure of 15MPa. We find that the transient and steady state hydrogen concentration fields in the neighborhood of the crack tip in the SENT specimen and the real-life pipeline are essentially the same. This environmental similitude warrants the use of the SENT specimen in a gaseous hydrogen environment to examine the compatibility of steel pipelines with hydrogen.

Dependence of Stress Corrosion Cracking of Alloy 690 on Temperature, Cold Work, and Carbide Precipitation—Role of Diffusion of Vacancies at Crack Tips

Abstract The growth rate of stress corrosion cracking (SCC) was measured for cold-worked, thermally treated Alloy 690 (UNS N06690, CW TT 690) and cold-worked, solution-treated Alloy 690 (CW ST 690) in hydrogenated pressurized water reactor (PWR) primary water under static load condition. Three important patterns were observed. First, intergranular stress corrosion cracking (IGSCC) was observed in CW TT 690 in PWR primary water in the range between 320°C and 360°C; this rate of SCC growth was slower than in CW mill-annealed Alloy 600 (UNS N06600, CW MA 600). No significant IGSCC was observed in CW ST 690 after 5,109 h in hydrogenated PWR primary water at 360°C. This is opposite of the behavior reported in the literature for high-temperature caustic solutions. Second, to assess the role of creep, rates of creep crack growth were measured in air, argon, and hydrogen gas environments using 20% CW TT 690 and 20% CW MA 600 in the range between 360°C and 460°C; intergranular creep cracking (IG creep cracking) wa...

Fretting Wear of a Bearing Steel in Hydrogen Gas Environment Containing a Trace of Water

Fretting wear tests on a bearing steel under gross slip condition were conducted in hydrogen and nitrogen gas environments containing water at 2 to 70 ppm using a new gas-tight chamber. Wear in hydrogen and nitrogen is sensitive to the water content of the gases and it increases as the water content increases. Water in these environmental gases reduces the coefficient of friction during the early cycles of experiments. Furthermore, exposure of the test specimens to high pressure hydrogen (40 MPa, 373 K, 200 hours) before the experiments enhances wear. These findings are consistent with the findings obtained in the authors' previous study, wherein the water content should have been higher and a comparison between hydrogen and nitrogen was not carried out because of insufficient control of water content. In this paper it is shown that wear in hydrogen is slightly larger than in nitrogen.

Investigation of Mechanism for Intergranular Fatigue Crack Propagation of Low Carbon Steel JIS S10C in Hydrogen Gas Environment

In order to investigate the mechanism for the intergranular fatigue crack propagation of a low carbon steel in a low pressure hydrogen gas environment, two kinds of examinations were carried out. One examined the effect of the cyclic pre-strain on the crack growth behavior. The other was the in-situ observation of intergranular fatigue crack propagation in a hydrogen gas environment. The main results are as follows. (1) SEM observation of the specimen surface morphology of a plain specimen fatigued in hydrogen gas showed that a gap at the grain boundary was induced by slip behavior, but not in nitrogen gas. (2) A specimen cyclic-prestrained in hydrogen gas showed slight influences on the increase in the crack propagation rate. (3) Mating intergranular facets on the fatigue fracture surfaces showed the matching of a striation-like pattern in the manner anticipated from the damage mechanism of (1). (4) The environment-change test from hydrogen to nitrogen during the fatigue test showed that intergranular facets appeared even in nitrogen. Results (3) and (4) suggests that the damaging process of (1) is valid in an actual fatigue crack. (5) In-situ observation of the crack propagation behavior in hydrogen gas showed that a crack propagated faster along the grain boundary. However, no visible discontinuous crack advances appeared as a large number of load repetitions was required. Phenomena considered to be a damage process (1) appeared ahead of a crack tip. Based on these results, a convincing mechanism for the intergranular fatigue crack propagation process is as follows. Grain boundaries just ahead of a crack tip are damaged due to the large number of hydrogen-enhanced slip repetitions, therefore, the fatigue crack becomes easier to propagate along the grain boundary in hydrogen.

Microscopic Observation of the Brittle-Striation Formation Mechanism in Low Carbon Steel Fatigued in Hydrogen Gas (TEM and EBSD Observation Corresponding to Fractography)

Observations by Transmission Electron Microscopy and Electron Backscatter Diffraction corresponding to Fractography were conducted in order to investigate the brittle-striation formation mechanism of low carbon steel JIS S10C in a hydrogen gas environment. The main results are as follows: (1) The quasi-cleavage (QC) facets plane with brittle-striations does not coincide with the (100) cleavage plane. (2) Slip deformation distributions reflecting the brittle-striation formation processes are observed by TEM. One of the conceivable brittle-striation formation mechanisms which can explain these results is as follows. A striation line is formed during the loading part of the cycle as a trace of blunting by slips. A stable ductile crack then starts growing. These processes are similar to those in the normal ductile fracture from a crack; that is, a ductile tearing process in tension.

Friction and Wear of Ferrous Materials in a Hydrogen Gas Environment

A novel technique was developed to control the concentration of water between 0.1 - 20 ppm and of oxygen between 0.3 - 2 ppm in hydrogen over a pin-on-disk apparatus. The developed technique simulates commercially available hydrogen gas at the point of use. This hydrogen usually contains sub-ppm to single-digit ppm levels of water and oxygen. The influence of impurities on the tribological properties of hardened chromium steel (JIS SUJ2) was obvious under the studied conditions, while the influence on austenitic stainless steel (JIS SUS316L) was not significant by comparison with that found in our previous study concerning higher water concentrations. The coefficient of friction of JIS SUJ2 increased with a decrease in the water concentration even at the smallest concentrations investigated in this study.

Investigation of the Mechanism for Brittle-Striation Formation in Low Carbon Steel Fatigued in Hydrogen Gas (Fractographic Observation on Fracture Processes Visualized by Controlling Load Sequence and Testing Environment)

In order to investigate the brittle-striation formation mechanism of a low carbon steel JIS S10C fatigued in a hydrogen gas environment, fractographic observations of the visualized fracture phenomena during some processes of brittle-striation formation were conducted. The following results were obtained. A striation line is formed during the loading part of the cycle as a trace of blunting by slip. A stable ductile crack then starts growing. These processes are similar to those during the normal ductile fracture from a crack; that is, a ductile tearing process in tension. Based on the experimental results, a brittle-striation formation model, in which hydrogen only enhances the microscopic ductile tearing process just ahead of a crack tip, was proposed. The model rationally explains the peculiar load-frequency effect in the quasi-cleavage range on the fatigue crack growth which reveals a lower growth rate in spite of lowering the load-frequency.

Loading-Frequency Effects on Fatigue Crack Growth Behavior of a Low Carbon Steel JIS S10C in Hydrogen Gas Environment

In order to clarify the loading-frequency effect on the fatigue crack growth behavior of a low carbon steel JIS S10C in a hydrogen gas environment, fully reversed bending fatigue tests were carried out. The main results are as follows. The loading-frequency effect on the FCG revealed a complex behavior; that is, not only acceleration, but also deceleration even in the same low loading-frequency range. The slight acceleration appears in the low growth rate range in which the ductile fracture mode is predominant. The deceleration appears due to the transition behavior from a quasi-cleavage fracture mode with a higher FCGR to a ductile one with a lower FCGR. This shows that lowering the load frequency does not necessarily lead to an unpredictable fatigue crack growth.

Fatigue Properties and Degradation Mechanism for Stainless and High Strength Steels in High Pressure Gaseous Hydrogen Environment

In order to ensure the safety of pipe and vessel used in high pressure gaseous hydrogen for fuel cell vehicles and hydrogen stations, material properties should be clarified and the mechanical structure needs to be designed. In this study, a cyclic pressurization fatigue test was conducted using tubular specimens in the high pressure gaseous hydrogen environment. Stable austenitic stainless steel SUS316L showed no degradation of fatigue life in high pressure gaseous hydrogen environment. In contrast, metastable austenitic stainless steel SUS304, precipitation hardening steel A-286 and low alloy steel SCM435 (high and low strength) showed degradation of fatigue life in high pressure gaseous hydrogen environment. Higher strengthened SCM435 showed degradation more significantly. It was clarified that the fatigue cracks grew along the interface between martensite phase and austenite phase in SUS304 with the use of Electron Back Scattering Diffraction Pattern (EBSD). Sub-cracks and intergranular fractures were observed in the fracture surface of A-286 which was tested in hydrogen environment. Intergranular fractures were observed in the fracture surface of high strengthened SCM435 and transgranular fractures were observed in the fracture surface of low strengthened SCM435 which was tested in hydrogen environment.

Smoothing of microfabricated silicon features by thermal annealing in reducing or inert atmospheres

In this work, high-temperature annealing of reactive ion etched silicon microstructures in H2 and Ar gases is studied. Three types of structural features were etched with four different masks into ⟨100⟩-oriented silicon wafers. Scanning electron microscope and atomic force microscope (AFM) results show that when smoothing due to surface diffusion and desorption of silicon is taking place in both the argon and hydrogen gas environments, the three types of features respond differently to the treatments. The surface diffusion was observed to be strongly dependent on temperature in argon, whereas the transport was more linear and controllable in the hydrogen gas environment. For hydrogen, AFM studies were performed to observe the details of the smoothing process. Finally, some potential applications of these transport phenomena are discussed.

A Review of Fatigue Crack Growth for Pipeline Steels Exposed to Hydrogen.

Hydrogen pipeline systems offer an economical means of storing and transporting energy in the form of hydrogen gas. Pipelines can be used to transport hydrogen that has been generated at solar and wind farms to and from salt cavern storage locations. In addition, pipeline transportation systems will be essential before widespread hydrogen fuel cell vehicle technology becomes a reality. Since hydrogen pipeline use is expected to grow, the mechanical integrity of these pipelines will need to be validated under the presence of pressurized hydrogen. This paper focuses on a review of the fatigue crack growth response of pipeline steels when exposed to gaseous hydrogen environments. Because of defect-tolerant design principles in pipeline structures, it is essential that designers consider hydrogen-assisted fatigue crack growth behavior in these applications.

Microstructure and Tensile Properties of ODS Ferritic Steels Produced by Mechanical Alloying in Argon and Hydrogen Gas Environments

Two types of oxide dispersion strengthened (ODS) ferritic steels have been produced by mechanical alloying (MA) either in argon or in hydrogen atmosphere, and vacuum hot pressing (VHP). A drastic reduction in the oxygen and nitrogen contents after VHP was strongly affected by hydrogen gas used as the MA atmosphere. MA in hydrogen was found to be effective for refining the steel matrix and enhancing the tensile ductility of the ODS ferritic steels.

Degradation of fatigue properties in high pressure gaseous hydrogen environment evaluated by cyclic pressurization tests

Fatigue properties in high pressure gaseous hydrogen environment were investigated for pipe materials used in fuel cell vehicles and hydrogen stations. Cyclic pressurization tests were conducted using a tubular specimen filled with hydrogen pressurized up to 90MPa. Tested materials were types 316L, 304 and A286 stainless steels, low alloy steels such as JIS SCM435 (1.0Cr-0.2Mo), Cr-Mo-V steels. The fatigue life in hydrogen was compared with that in inert gas to evaluate the effect of gaseous hydrogen on fatigue properties. The fatigue life in hydrogen was slightly shorter than that in argon in the case of a stable stainless steel type 316L. In contrast, a metastable stainless steel type 304 showed a remarkable degradation of the fatigue life in the hydrogen environment. Although the fatigue lives in hydrogen of type 316L and 304 stainless steels decreased with the increase in the cycle times, the fatigue lives remained unchanged over 102 of the cycle time. The fatigue life of low alloy SCM435 steel in hydrogen extremely decreased. The fatigue life of high-strength austenitic steel A286 in hydrogen is much better than that of low alloy SCM435 steel at the same tensile strength. The Cr-Mo-V steels showed longer fatigue lives than JIS SCM 435 at same strength levels in hydrogen. Fracture surfaces revealed transgranular cracking for the Cr-Mo-V steels, while intergranular cracking was observed for SCM435 with tensile strength more than 1.2 GPa. It was assumed that the carbide precipitation affected the fracture morphology.