Apparent Hydrogen Diffusivity Research Articles

Hydrogen permeation in iron-chromium-aluminum (FeCrAl) alloys and the effects of microstructure and surface oxide

Iron–chromium–aluminum (FeCrAl) class alloys are candidates for use as cladding for accident-tolerant fuels and moderators. In this context, hydrogen isotope permeation in FeCrAl alloys is an important material property. In the present work, the apparent permeability, effective diffusivity, and apparent solubility of hydrogen in the FeCrAl alloys C26M and Kanthal D (KD) were measured with gas-driven hydrogen permeation. Permeation measurements were conducted at temperatures of 400 to 700 °C and at gas-driven pressures from 1 to 100 kPa. In particular, the effect of grain size on hydrogen transport was studied with KD samples with three different microstructures: nanocrystalline (NC), ultra-fine grained (UFG), and coarse-grained (CG). The UFG and NC specimens had higher apparent activation energies (73.4 kJ mol-1 and 65.2 kJ mol-l, respectively) for hydrogen permeability than the CG sample (46.9 kJ mol-1). An aluminum oxide layer formed on the primary- and secondary-side surfaces of all samples subjected to permeation experiments which demonstrated the propensity of FeCrAl alloys to form these innate oxide permeation barriers.

Grain refinement's effect on hydrogen embrittlement of 304 austenitic stainless steel: A comparative investigation of hydrogen in-situ charging vs. pre-charging

Controversy surrounds the potential of grain refinement in suppressing metal hydrogen embrittlement (HE). The literature presents two methods for introducing hydrogen into metals: hydrogen pre-charging (HPC) and hydrogen in-situ charging (HISC). This study compares the effect of grain refinement on HE under electrochemical HPC and HISC conditions, focusing on type 304 austenitic stainless steel with a grain size range of 0.5–35 μm. HE behaviors were evaluated through tensile testing and fracture morphology analyses, while hydrogen diffusion and concentration were examined using hydrogen uptake amount measurements and hydrogen permeation tests, complemented by finite element (FE) simulations. Results indicate that coupling with plastic deformation significantly accelerated hydrogen transport in the HISC condition, leading to higher apparent hydrogen diffusivity compared to the HPC condition, with grain boundaries (GBs) act as hydrogen traps. Under the HISC, grain refinement reduced HE susceptibility by decreasing the apparent diffusivity due to an increased trapping effect of GBs and suppressing intergranular fracture by reducing the hydrogen amount distributed to each GB (hydrogen occupancy of the GBs). However, grain refinement to below 1 μm increased HE under the HPC condition. Hydrogen permeation tests showed that under the HPC, grain refinement slightly decreased hydrogen diffusivity. In the ultrafine-grained specimen, as GBs trapped more hydrogen atoms, they not only provided hydrogen to stress-concentrated lattices and newly-formed dislocations by detrapping but also maintained a higher hydrogen occupancy of the GBs, thus increasing HE. It is concluded that whether grain refinement suppresses HE depends primarily on the resulting hydrogen occupancy of the GBs, which is influenced by the charging conditions rather than the quantity of traps.

Hydrogen transport in 17−4 PH stainless steel: Influence of the metallurgical state on hydrogen diffusion and trapping

The recent interest for dihydrogen concerning its ability to decarbonize numerous sectors of our society highlighted the necessity to develop alloys combining high mechanical properties and good resistance to hydrogen embrittlement. With this in mind, the 17–4 PH precipitation hardened stainless steel was studied in order to understand the interactions between hydrogen and the different microstructural elements. Advanced physicochemical characterizations (XRD, SEM, ACOM/TEM) were coupled with electrochemical permeation tests on different metallurgical states of 17–4 PH alloy. The apparent hydrogen diffusivity was around 10−13 m2.s−1 at 23 °C and was found highly dependent on the microstructure. More specifically, when copper precipitates were fine, the copper precipitates/matrix interfaces were found to be the major trapping site. In addition, nature of these interfaces, which can be varied depending on thermal treatments, seemed to influence reversibility of the trapping.

Investigation of Hydrogen Diffusion in High Hardness Steels

Development of high hardness steels (HHS) for use in armor, shipbuilding, construction and automotive requires investigation into their sensitivity to hydrogen embrittlement. Hydrogen embrittlement, often caused by environmental corrosion, significantly impairs the mechanical properties of steel, producing increased local hardness and increased likelihood of catastrophic brittle failure. Mitigation of embrittlement can employ the introduction of hydrogen traps or phase barriers into the steel. In this work, we employed the Devanathan-Stachurski method to investigate the diffusion of hydrogen atoms through a steel membrane. The effect of strong hydrogen trapping was observed as an apparent change in hydrogen diffusivity from the initial and subsequent diffusion trials. We compared three different high hardness steel samples and used two methods to determine the apparent diffusivity and number of strong and weak hydrogen traps. Metallographic analysis of the samples illustrates the effect of composition on the diffusivity data. Figure 1

Effect of Microstructure on the Mechanical Properties and Fracture Toughness of API X65 Pipeline Steel in the Presence of Hydrogen

This study investigated the influence of microstructure on the mechanical properties and fracture toughness of API X65 pipeline steel in the presence of hydrogen. In this study, electrochemical method was used for hydrogen charging and indentation technique was applied to obtain the fracture toughness. The results showed that in the presence of hydrogen, elongation (EL%), reduction of area (RA), ductile fracture percentage, and fracture toughness of all microstructures decreased. The microstructure of martensite (M) + bainite (B) + ferrite (F), had the highest hydrogen trapping and uptake (Capp) as 8.58 × 10–6 mol cm−3 and the lowest apparent hydrogen diffusivity (Dapp) as 5.68 × 10−10 m2 s−1; thus, the maximum decrements of 33% in fracture toughness, 40% in ductile fracture percentage, 47% in RA, and 35% in EL% were observed. However, the microstructure of ferrite (F) + degenerated perlite (DP) + martensite-austenite micro constituent (M/A), where the lowest value of 5.85 × 10–6 mol cm−3 for Capp and the highest value of 8.5 × 10–10 m2 s−1 for Dapp had the minimum decrements as 2% in fracture toughness, 10% in ductile fracture percentage, 4% in RA, and 7% in El%. According to the obtained results, depending on the type of microstructures, hydrogen-induced work softening or hardening were observed by decreasing or increasing the yield stress respectively.

Effects of deep geological environments for nuclear waste disposal on the hydrogen entry into titanium

Abstract The surface of nuclear waste container will be completely wetted by the groundwater infiltrating through the bentonite or concrete buffer after the closure of its deep geological disposal. Because of its excellent corrosion resistance, titanium is one of the candidates for the container materials for high-level nuclear waste (HLNW) disposal. However, once oxygen depleted in the large time scale deep geological disposal, titanium container will suffer from hydrogen embrittlement (HE). Therefore, in order to predict the potential danger of the HLNW container caused by HE, the hydrogen entry into titanium was studied at different temperatures in simulated deep geological environment of Beishan, which is the preselected HLNW disposal area in China. Devanathan-Stachurski cell methods were firstly implemented in measuring apparent hydrogen diffusivity in titanium with hydrides being formed during hydrogen charging at low temperature ranges (298–373 K). Given the characteristic of the Devanathan-Stachurski cell method's capable of getting apparent diffusivity with combined influencing factors easily, the technique provides a simple way to measure the parameter that is necessary for the estimation of hydrogen penetration depth, facilitating the design of HLNW containers.

Combined effects of prior plastic deformation and sensitization on hydrogen embrittlement of 304 austenitic stainless steel

Austenite stainless steels (ASSs) may suffer from both cold deformation and sensitization prior to hydrogen exposure. There is scant data in literature on the combined effect of prior deformation and sensitization on the hydrogen embrittlement (HE) of ASSs. The present study investigated the combined effects of tensile plastic prestrain (PS) and 650 °C sensitization (ST) on the HE of 304 steel by hydrogen pre-charging and tensile testing. The results are explained by terms of pre-existing α′ martensite content. PS higher than 10% can enhance HE significantly by inducing severe α′ transformation prior to hydrogen exposure. Prior ST also enhances HE, but submitting the prestrained and α′-containing 304 steel to short-time ST can diminish the enhancement of HE by prestraining, as ST can cause the reversion of α′ to austenite, reducing pre-existing α′ content. It is inadvisable to make 304 steel be sensitized/welded firstly and deformed subsequently, even if the ST time is short such as what happens during welding, because this treating sequence can induce more α′ than prestraining alone, enhancing HE more significantly. Apparent hydrogen diffusivity can be related quantitatively to pre-existing α′ content, proving directly that α′ platelets can act as diffusion “highways” in ASSs. It is indicated that pre-existing α′ can enhance subsequently the HE of ASSs is because it can lead to a large amount of hydrogen entering the ASSs during hydrogen exposure by acting as diffusion “highways”. HE is enhanced by increasing hydrogen amount rather than by pre-existing α′ itself.

Effect of α′ Martensite Content Induced by Tensile Plastic Prestrain on Hydrogen Transport and Hydrogen Embrittlement of 304L Austenitic Stainless Steel

Effects of microstructural changes induced by prestraining on hydrogen transport and hydrogen embrittlement (HE) of austenitic stainless steels were studied by hydrogen precharging and tensile testing. Prestrains higher than 20% at 20 °C significantly enhance the HE of 304L steel, as they induce severe α′ martensite transformation, accelerating hydrogen transport and hydrogen entry during subsequent hydrogen exposure. In contrast, 304L steel prestrained at 50 and 80 °C and 316L steel prestrained at 20 °C exhibit less HE, due to less α′ after prestraining. The increase of dislocations after prestraining has a negligible influence on apparent hydrogen diffusivity compared with pre-existing α′. The deformation twins in heavily prestrained 304L steel can modify HE mechanism by assisting intergranular (IG) fracture. Regardless of temperature and prestrain level, HE and apparent diffusivity ( D app ) increase monotonously with α′ volume fraction ( f α ′ ). D app can be described as log D app = log ( D α ′ s α ′ / s γ ) + log [ f α ′ / ( 1 − f α ′ ) ] for 10 % < f α ′ < 90 % , with D α ′ is diffusivity in α′, s α ′ and s γ are solubility in α′ and austenite, respectively. The two equations can also be applied to these more typical duplex materials containing both BCC and FCC phases.

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.

Vapor-deposited iron sulfide films as a novel hydrogen permeation barrier for steel: Deposition condition, defect effect, and hydrogen diffusion mechanism

Hydrogen embrittlement is a serious problem in the oil/gas industry. In this work, various iron sulfide (FeS) films, including iron monosulfide (FeS), pyrite (FeS2), and pyrrhotite (Fe7S8), were synthesized in X80 steel by chemical vapor deposition at 200 °C, 300 °C, 400 °C, and 500 °C. The corrosion resistance and hydrogen permeation properties of the FeS films were investigated through electrochemical methods. Results indicated that FeS films significantly improved the hydrogen barrier properties of the X80 steel, which was closely related to the crystal structure type and defects of FeS films. Defects like microcracks and pinholes during deposition can increase the porosity of the film, resulting in the film properties decreased. Moreover, FeS film (at 300 °C), which had the smallest apparent hydrogen diffusivity (D ˜ 2.64 × 10−7 cm2/s) and apparent subsurface concentration (Capp ˜ 1.12 μmol/cm3), had the best hydrogen barrier properties. The corrosion resistance of FeS film (300 °C) was excellent.

Hydrogen Embrittlement in Advanced High Strength Steels and Ultra High Strength Steels: a new investigation approach

In order to reduce CO2 emissions and fuel consumption, and to respect current environmental norms, the reduction of vehicles weight is a primary target of the automotive industry. Advanced High Strength Steels (AHSS) and Ultra High Strength Steel (UHSS), which present excellent mechanical properties, are consequently increasingly used in vehicle manufacturing. The increased strength to mass ratio compensates the higher cost per kg, and AHSS and UHSS are proving to be cost-effective solutions for the body-in-white of mass market products.In particular, aluminized boron steel can be formed in complex shapes with press hardening processes, acquiring high strength without distortion, and increasing protection from crashes. On the other hand, its characteristic martensitic microstructure is sensitive to hydrogen delayed fracture phenomena and, at the same time, the dew point in the furnace can produce hydrogen consequently to the high temperature reaction between water and aluminum. The high temperature also promotes hydrogen diffusion through the metal lattice under the aluminum-silicon coating, thus increasing the diffusible hydrogen content. However, after cooling, the coating acts as a strong barrier preventing the hydrogen from going out of the microstructure. This increases the probability of delayed fracture. As this failure brings to the rejection of the component during production, or, even worse, to the failure in its operation, diffusible hydrogen absorbed in the component needs to be monitored during the production process.For fast and simple measurements of the response to diffusible hydrogen of aluminized boron steel, one of the HELIOS innovative instruments was used, HELIOS II. Unlike the Devanathan cell that is based on a double electrochemical cell, HELIOS II is based on a single cell coupled with a solid-state sensor. The instrument is able to give an immediate measure of diffusible hydrogen content in sheet steels, semi-products or products, avoiding time-consuming specimen palladium coating with a guided procedure that requires virtually zero training.Two examples of diffusible hydrogen analyses are given for Usibor®1500-AS, one before hot stamping/ quenching, and one after hot stamping, suggesting that the increase in the number of dislocations during hot stamping could be the main responsible for the lower apparent diffusivity of hydrogen.

Study on the Hydrogen Embrittlement of Aermet100 Using Hydrogen Permeation and SSRT Techniques

Aermet100 steel suffers greatly from hydrogen embrittlement due to its ultra-high strength. During the corrosion process as part of its service life, reduction of H+ in an acidic environment and H2O in a deaerated near-neutral environment are the main sources of hydrogen generation. Hydrogen permeation into Aermet100 steel can occur even in the atmosphere. After tempering, the coherent precipitations can hinder diffusion of hydrogen in the tempered steel, causing the apparent hydrogen diffusivity and steady hydrogen permeation current to decrease. The fracture morphology of tempered Aermet100 steel after a slow strain rate test in an acidic solution is predominantly micro-void coalescence with few inner cracks. As the solution pH decreases, micro-cracks initiate not only on the side surface but also within the steel. Coalition of micro-cracks accelerates the overall cracking process.

Design of (Nb, Mo)40Ti30Ni30 alloy membranes for combined enhancement of hydrogen permeability and embrittlement resistance

The effect of substitution of Nb by Mo in Nb40Ti30Ni30 was investigated with respect to microstructural features and hydrogen dissolution, diffusion and permeation. As-cast Nb40−xMoxTi30Ni30 (x = 0, 5, 10) alloys consist of primary bcc-Nb phase and binary eutectic (bcc-Nb + B2-TiNi). The substitution of Nb by Mo reduces the hydrogen solubility in alloys, but may increase (x = 5) or decrease (x = 10) the apparent hydrogen diffusivity and permeability. As-cast Nb35Mo5Ti30Ni30 exhibits a combined enhancement of hydrogen permeability and embrittlement resistance as compared to Nb40Ti30Ni30. This work confirms that Mo is a desirable alloying element in Nb that can contribute to a reduction in hydrogen absorption and an increase in intrinsic hydrogen diffusion, thus improving embrittlement resistance with minimal permeability penalty.

Effect of bainite in microstructure on hydrogen diffusion and trapping behavior of ferritic steel used for sour service application

Abstract

Effect of shot peening on hydrogen embrittlement of high strength steel

The effect of shot peening (SP) on hydrogen embrittlement of high strength steel was investigated by electrochemical hydrogen charging, slow strain rate tensile tests, and hydrogen permeation tests. Microstructure observation, microhardness, and X-ray diffraction residual stress studies were also conducted on the steel. The results show that the shot peening specimens exhibit a higher resistance to hydrogen embrittlement in comparison with the no shot peening (NSP) specimens under the same hydrogen-charging current density. In addition, SP treatment sharply decreases the apparent hydrogen diffusivity and increases the subsurface hydrogen concentration. These findings are attributed to the changes in microstructure and compressive residual stress in the surface layer by SP. Scanning electron microscope fractographs reveal that the fracture surface of the NSP specimen exhibits the intergranular and quasi-cleavage mixed fracture modes, whereas the SP specimen shows only the quasi-cleavage fractures under the same hydrogen charging conditions, implying that the SP treatment delays the onset of intergranular fracture.

Determining the Directionally-Dependent Effective Hydrogen Diffusivity of High Strength Steel Strand

<p class="1Body">An important factor in the Hydrogen Embrittlement (HE) of cold-worked carbon steel strand is the effective hydrogen diffusivity of the strand material. The speed at which HE can occur is determined by the transport of the hydrogen to locations of stress concentrations. A Scanning Kelvin Probe (SKP) was used to measure the flattened surface of strand wires before and after being charged with hydrogen to determine a relationship between the delta work function measured (and indirectly the potential of the specimen) and the presence of hydrogen near the surface of that area of the specimen. Numerous scans were performed to determine a change in delta work function between the probe and the specimen. This change in delta work function was related to the presence of hydrogen at the specimen surface over time, giving a rate of hydrogen movement within a specific area of the specimen (both in the radial and drawn directions). The change in delta work function over time was then related to the diffusion of hydrogen over time in a given area resulting in a directional effective diffusivity of hydrogen through the strand which includes the effects of hydrogen trapping and method of hydrogen transport.</p><p class="1Body">The results indicate that the effective or apparent hydrogen diffusivity in the drawn direction in pearlitic, cold worked, carbon steel strand is 5.24E-08 cm<sup>2</sup>/sec. The effective hydrogen diffusivity in the radial direction was faster (3.56E-07 cm<sup>2</sup>/sec) as compared to the wire drawn direction.</p>

Determining the Directionally-Dependent Effective Hydrogen Diffusivity of High Strength Steel Strand

<p class="1Body">An important factor in the Hydrogen Embrittlement (HE) of cold-worked carbon steel strand is the effective hydrogen diffusivity of the strand material. The speed at which HE can occur is determined by the transport of the hydrogen to locations of stress concentrations. A Scanning Kelvin Probe (SKP) was used to measure the flattened surface of strand wires before and after being charged with hydrogen to determine a relationship between the delta work function measured (and indirectly the potential of the specimen) and the presence of hydrogen near the surface of that area of the specimen. Numerous scans were performed to determine a change in delta work function between the probe and the specimen. This change in delta work function was related to the presence of hydrogen at the specimen surface over time, giving a rate of hydrogen movement within a specific area of the specimen (both in the radial and drawn directions). The change in delta work function over time was then related to the diffusion of hydrogen over time in a given area resulting in a directional effective diffusivity of hydrogen through the strand which includes the effects of hydrogen trapping and method of hydrogen transport.</p><p class="1Body">The results indicate that the effective or apparent hydrogen diffusivity in the drawn direction in pearlitic, cold worked, carbon steel strand is 5.24E-08 cm<sup>2</sup>/sec. The effective hydrogen diffusivity in the radial direction was faster (3.56E-07 cm<sup>2</sup>/sec) as compared to the wire drawn direction.</p>

Hydrogen effects on the microstructure of a 2.25Cr–1Mo–0.25 V steel welded joint

The effect of hydrogen in a 2.25Cr–1Mo–0.25 V steel welded joint was studied using tensile mechanical and hydrogen permeation tests. Hydrogen diffusivity and solubility were determined by electrochemical (room temperature) and gas permeation (350–500 °C) tests. The hydrogen permeation curve for the base metal, at room temperature exhibited a strong deviation of sigmoidal shape indicating the influence of deep traps as martensite and austenite phases. The hydrogen solubility at room temperature obtained for the base material was equal to 21.8 molH m−3. At high temperatures (350–500 °C) the apparent hydrogen diffusivity was: D=1.3·10−6exp(−32.2±4kJ/molRT) m2 s−1 for the base metal and D=2.0·10−7exp(−27.3±3kJ/molRT) m2 s−1 for the weld metal. Stress–strain tests revealed that in the hydrogenated samples, applying elastic stress, there was increase of hydrogen embrittlement of this alloy due to the enhancement of hydrogen solubility.

Investigation of hydrogen transport behavior of various low-alloy steels with high-pressure hydrogen gas

The apparent hydrogen diffusivity and the saturated hydrogen content of Cr–Mo and Ni–Cr–Mo steels were determined with high-pressure hydrogen gas. Surface effects on hydrogen entry and exit were also investigated by using palladium-coated samples and by diffusion analysis using the finite-element method. Hydrogen contents of hydrogen-exposed cylindrical specimens of various sizes were measured by means of gas chromatography–mass spectrometry to obtain the saturated hydrogen content. The diffusivity was determined by fitting the solution of a diffusion equation to the experimental hydrogen contents determined by desorption at various constant temperatures. In the specimens examined, surface effects were significant at room temperature. The temperature dependences of the diffusivity were reasonably consistent with reference data mainly measured with electrochemical charging. These results were interpreted in terms of hydrogen trapping. Ordinary electrochemical charging represents a more severe condition than exposure to high-pressure hydrogen, for example, at 100 MPa.

Electrochemical investigation on the hydrogen permeation behavior of 7075-T6 Al alloy and its influence on stress corrosion cracking

The hydrogen permeation behavior and stress corrosion cracking (SCC) susceptibility of precharged 7075-T6 Al alloy were investigated in this paper. Devanthan–Stachurski (D-S) cell tests were used to measure the apparent hydrogen diffusivity and hydrogen permeation current density of specimens immersed in 3.5wt% NaCl solution. Electrochemical experiment results show that the SCC susceptibility is low during anodic polarization. Both corrosion pits and hydrogen-induced cracking are evident in scanning electron microscope images after the specimens have been charging for 24 h.