Hydrogen Embrittlement Sensitivity Research Articles

Hydrogen-assisted cracking in 2205 duplex stainless steel: Initiation, propagation and interaction with deformation-induced martensite

The present work evaluates hydrogen-assisted cracking in 2205 duplex stainless steel by performing electron backscatter diffraction (EBSD) on in-situ hydrogen charged tensile tested specimens. The hydrogen embrittlement sensitivity increases with the electrochemical hydrogen charging time. The hydrogen presence results in deformation-induced martensite formation in the austenite during in-situ tensile straining, which starts immediately after yielding. Hydrogen-assisted cracking starts at a later stage in the tensile test and the cracks mainly initiate in austenite. The deformation-induced martensite is not vulnerable for crack initiation, neither is its interface with the austenite matrix. The presence of hydrogen-assisted cracks depends on the strain level reached in the specimen and is therefore most pronounced in the necked region. Crack propagation occurs through austenite, ferrite and their interface and is mainly governed by strain fields. Finally, propagation also occurs by coalescence of several smaller cracks.

Effect of Relative Humidity on Mechanical Degradation of Medium Mn Steels.

Medium Mn steels have been considered as the next-generation materials for use in the automotive industry due to their excellent strength and ductility balance. To reduce the total weight and improve the safety of vehicles, medium Mn steels look forward to a highly promising future. However, hydrogen-induced delayed cracking is a concern for the use of high strength steels. This work is focused on the service characteristics of two kinds of medium Mn steels under different relative humidity conditions (40%, 60%, 80% and 100%). Under normal relative humidity (about 40%) at 25 °C, the hydrogen concentration in steel is 0.4 ppm. When exposed to higher relative humidity, the hydrogen concentration in steel increases slowly and reaches a stable value, about 0.8 ppm. In slow strain rate tensile tests under different relative humidity conditions, the tensile strength changed, the hydrogen concentration increased and the elongation decreased as well, thereby increasing the hydrogen embrittlement sensitivity. In other words, the smaller the tensile rate applied, the greater the hydrogen embrittlement sensitivity. In constant load tests under different relative humidity conditions, the threshold value of the delayed cracking of M7B (‘M’ referring to Mn, ‘7’ meaning the content of Mn, ‘B’ denoting batch annealing) steel maintains a steady value of 0.82 σb (tensile strength). The threshold value of the delayed cracking of M10B significantly changed along with relative humidity. When relative humidity increased from 60% to 80%, the threshold dropped sharply from 0.63 σb to 0.52 σb. We define 80% relative humidity as the ‘threshold humidity’ for M10B.

The hydrogen embrittlement sensitivity of duplex stainless steel with different phase fractions evaluated by in-situ mechanical testing

The influence of the austenite (gamma) phase fraction on the hydrogen embrittlement of duplex stainless steel is investigated. Heat treatments are performed to create two duplex stainless steel specimens, containing 50% and 44% of austenite, respectively. Mechanical testing with and without hydrogen charging reveals that significant embrittlement occurs regardless of the austenite fraction. A higher austenite fraction results in a reduced ductility loss under the presence of hydrogen. Samples with a higher ferrite fraction are embrittled more due to their higher hydrogen diffusivity. In-situ tensile tests, interrupted at the ultimate tensile strength, show hydrogen-assisted cracks on the specimen surface both in austenite and ferrite and across the alpha/gamma interface.

New Rapid prototyping technology for the prevention of hydrogen embrittlement of metal strips

Hydrogen embrittlement is a serious concern for advanced steels. In this research, twin-roll strip vibration cast-rolling was developed independently as a novel method for steel strip industrial production that inhibits hydrogen embrittlement. It reduces the hydrogen embrittlement sensitivity by optimizing the microstructure of strip steel products during the manufacturing process. Control experiments and cross-scale simulations were performed to reveal the phenomena and mechanisms that inhibit hydrogen embrittlement. The results show that the twin-roll strip vibration cast-rolling process can effectively reduce the hydrogen embrittlement sensitivity of steel strips.

Effect of strain rate on environmental hydrogen embrittlement susceptibility of a severely cold-rolled Al–Cu alloy

This study investigated the effect of strain rate ranging between 1.7 × 10−4 and 1.7 × 10−8 s−1 on environmental hydrogen embrittlement behavior in a severely cold-rolled Al–Cu alloy. Elongations of the specimens tensile-tested in humid air (HA) decreased significantly compared with the specimens tensile-tested in dry nitrogen gas at strain rates of 1.7 × 10−5, 1.7 × 10−6 and 1.7 × 10−7 s−1. With decreasing the strain rate, the hydrogen embrittlement sensitivity (HES) index of the alloy first increased and then decreased with the maximum occurring at 1.7 × 10−6 s−1, exhibited a largest amount of desorbed hydrogen. The characteristics of the fracture behavior of the specimens tensile-tested in HA also changed with the strain rate. Thermal desorption spectroscopy results revealed that the amount of trapped hydrogen at dislocations and/or second phase particles has a correlation with HES index.

Effect of laser peening with different power densities on vibration fatigue resistance of hydrogenated TC4 titanium alloy

Laser peening (LP) treatment with different power densities was used to improve the vibration fatigue resistance of hydrogenated TC4 titanium alloy. Compressive residual stress (CRS), micro-hardness and micro-structure of hydrogenated LPed specimens were firstly measured. Vibration fatigue test was then carried out to compare the fatigue life and fractures of LPed and non-LPed hydrogenated specimens. It was found that LP-induced high level CRS suppressed the permeation of hydrogen atoms through material surface, which may reduce the hydrogen embrittlement sensitivity. The CRS also prohibited the fatigue crack initiation and propagation by increasing the fatigue limit and crack propagation threshold of hydrogenated specimen. Grain morphologies of α phase and β phase were refined after LP. Beneficial crystal defects inside the α phase and β phase tangled more free hydrogen atoms, which was believed to be crucial factors to inhibit the generation of initial hydrogen-induced crack. Fracture morphologies further confirmed that LP changed the location of fatigue crack initiation (FCI) and slowed down the fatigue crack growth (FCG) rate of hydrogenated specimens. Finally, a strengthening mechanism of LP on the vibration fatigue resistance of hydrogenated specimen was proposed.

A study of annealing time to surface characteristics and hydrogen embrittlement on AlSi coated 22MnB5 during hot stamping process

Hydrogen embrittlement is influenced by material sensitivity, residual stress and hydrogen uptake. During hot stamping process, there are various factors that affect hydrogen embrittlement, such as annealing time during the heating process. As the annealing time increases, the color of the metallic coating gradually turns from blue to red and microstructure becomes larger. When the surface properties of automotive steel are changed, it is necessary to check whether there is any problem in electro-coating process and corrosion resistance. In this study, we investigated the effect of the metallic layers by diffusion of Fe and defect sensitivity resulting of the electrocoating process such as pinhole, corrosion resistance and hydrogen embrittlement sensitivity of steel, with annealing time in the hot stamping heating furnace. Coating workability shows similar results regardless of annealing time, but the sensitivity of hydrogen embrittlement is greatly influenced by annealing time in the hot-stamping furnace. And we have found a way to manage optimal annealing time to reduce of hydrogen embrittlement sensitivity on hot stamping steel by chroma- meter.

Hydrogen charging of Al–Mg–Si-based alloys by friction in water and its effect on tensile properties

In order to introduce high amounts of hydrogen into aluminum alloys, hydrogen charging in peak-aged Al–Mg–Si-based alloys (A6061-T6) by means of friction in water (FW) was investigated and the hydrogen embrittlement (HE) sensitivity of the samples was evaluated. Al–Mg–Si alloys containing different amounts of iron (from 0.1 to 0.7 mass %) were prepared in order to clarify the effect of iron on the HE sensitivity. Hydrogen charging was carried out by polishing the alloy surface for 1 h with a silicon carbide emery paper in water at room temperature. For comparison, hydrogen-uncharged alloy specimens were also prepared. The total amount of hydrogen in the Al–Mg–Si alloys clearly increased after the FW process, during which hydrogen was generated by the chemical reaction between water and the non-oxide coated aluminum alloys. After hydrogen charging by the FW process, the Al–Mg–Si alloy with a low iron content (0.1 mass %) showed a decrease in ductility in conventional strain rate tensile testing; conversely, alloys with higher iron contents (0.2 and 0.7 mass %) did not show a decrease in ductility. This suggests that peak-aged Al–Mg–Si alloys with high iron contents are less sensitive to HE.

Hydrogen embrittlement sensitivity of X100 pipeline steel under different pre-strain

In the present study, the influences of hydrogen on the mechanical properties as well as the pre-strain on the HE susceptibility of X100 pipeline steel were investigated by combining electrochemical hydrogen charging and tensile experiments. Both the yield and tensile strength decrease with the increasing hydrogen charging time no matter the values of pre-strain. When the charging time is 12 h, the yield strength and tensile strength was reduced by 3% and 9%, respectively. The longer the charging time, the stronger the HE damage of the steel. Besides, when the hydrogen charging time is same, HE sensitivity increases with the pre-strain values. When the charging time is 6 h, the HE sensitivity coefficient is 40.24% without pre-strain, and it increases to 49.26% with the pre-strain value increases to the 2%. The hydrogen effective diffusion coefficient reduces gradually with the increasing pre-strain values. The coefficient is 5.45 × 10−7 cm2/s without pre-strain and it reduces to 1.21 × 10−7 cm2/s with the pre-strain value increases to the 3%. When the hydrogen charging time is same, HE sensitivity increases with the pre-strain values.

Hydrogen embrittlement risk control of prestressed tendons during electrochemical rehabilitation based on bidirectional electro-migration

Abstract Bidirectional electro-migration rehabilitation (BIEM) is type of electrochemical rehabilitation that allows for simultaneous chloride ion removal and inhibitor injection into the steel bar surface. The inhibitor migrates across the surface of the steel bar, altering its pH and forming a thin layer of isolation that reduces hydrogen evolution. In this paper, sensitivity of hydrogen embrittlement was studied using constant strain rate tensile analysis, fracture energy ratio, and fracture morphology. When compared with electrochemical chloride extraction (ECE), BIEM treatment enhanced the critical current density and reduced the stripes number in radical zone. The fracture energy ratio remained at a high level, even with a current density and BIEM treatment time that were no more than 3 A/m2 and 14 d respectively. The results indicated that the sensitivity of prestressed tendons to hydrogen embrittlement after BIEM was markedly lower than that after ECE. Collectively, these results indicate that BIEM treatment can mitigate the application limitations of the current electrochemical rehabilitation technology used on prestressed concrete structures.

Effects of source of hydrogen entry on hydrogen embrittlement sensitivity of Al–Zn–Mg base alloys with high amount of zinc

Effects of source of hydrogen entry on hydrogen embrittlement sensitivity of Al–Zn–Mg base alloys with high amount of zinc

Effect of static hydrogen charging on corrosion and hydrogen embrittlement of High strength steel

The corrosion and hydrogen embrittlement properties of 1000MPa grade high strength steel in sea water are studied by weightlessness test under the condition of cathode polarization and slow strain tensile test (SSRT) after static hydrogen filling . The fracture characteristics of the specimen are observed with SEM. The results show that the most positive cathodic protection potential of high strength steel in sea water is -780 mV. The tensile test shows that with the negative shift of the polarization potential and the increase of hydrogen charging time, the elongation and the shrinkage of the high strength steel decrease gradually. The fracture mode transforms from ductile to cleavage and intergranular fracture. It can be seen that the toughness of the material decreases and the hydrogen embrittlement sensitivity increases gradually. Especially, the effect of polarization potential on hydrogen embrittlement of materials is more obvious.

Hydrogen embrittlement susceptibility of a Ni-16Mo-7Cr base superalloy

This study investigated the hydrogen embrittlement sensitivity of a Ni-16Mo-7Cr base superalloy under different hydrogen pre-charging states. Detailed electromicroscopy characterization has been employed on the hydrogen pre-charged alloy after tensile testing to understand the mechanism of hydrogen-assisted cracking. The results show that the tensile strength of the alloy is remarkably decreased with the increasing of hydrogen pre-charging time, whereas the yield strength remains stable all the time. The fractographic study combined with ECCI analysis by Scanning Electron Microscopy demonstrates that the cracks propagated predominantly along the grain boundary in the presence of hydrogen, and a few can propagate along planar dislocation slip bands (DSBs) especially along the intersections between nonparallel DSBs. The proposed hydrogen embrittlement mechanism for the Ni-16Mo-7Cr base superalloy is that the coalescence and widening of the nano-voids, which are resulted from the interaction between the hydrogen and dislocations, cause the crack initiation and propagation along the grain boundary, and further cause the alloy intergranular fracture.

Strengthening mechanism and hydrogen-induced crack resistance of AISI 316L stainless steel subjected to laser peening at different power densities

Microstructural response of AISI 316L stainless steel to laser peening (LP) was examined by means of optical microscopy (OM) and transmission electron microscopy (TEM) in order to analyze the effects of LP on hydrogen-induced cracking (HIC) resistance. Depth profiles of near-surface microhardness and surface compressive residual stress (CRS) of LP treated specimens were presented respectively. Slow strain rate tensile tests were performed on the hydrogen-charged samples and their corresponding stress-strain curves as well as fracture morphologies were finally investigated in detail. The results demonstrated that LP induced a grain refinement effect on the treated surface while a maximum refining rate of 56.18% was achieved at the laser power density of 10 GW/cm2. The near-surface microhardness also exhibited an attenuation trend with the increasing depth. The surface CRS positively correlated with power density before it reached a threshold value. A special U-shaped dislocation tangle band was observed in the LP treated specimen which served as hydrogen trapping sites. The LP treated samples exhibited better toughness after hydrogen charging from both macro mechanical properties and micro fracture morphologies. LP-induced grain refinement and CRS are believed to be the main contributing factors towards inhibiting the diffusion of hydrogen atoms which ultimately leads to the reduction of the hydrogen embrittlement sensitivity of AISI 316L stainless steel.

Study of the effect of hydrogen charging on the tensile properties and microstructure of four variant heat treatments of nickel alloy 718

This study examined the hydrogen embrittlement sensitivity of nickel alloy 718 given four different heat treatments to obtain various microstructural states. The four heat treatments examined are the oil and gas 718 heat treatment, the aerospace 718 heat treatment, and two variant two-step heat treatments, with a difference in aging heat treatment named 718 low band and high band. Each heat treatment leads to differences in the precipitate morphologies of γ′, γ′′ and δ phases.Material characterisation and fractography of the examined heat treatments were performed using a high resolution FEG SEM. Three specimens of each condition were pre-charged with hydrogen and tensile properties were compared with those of non-charged specimens. It was observed that hydrogen embrittlement was associated with intergranular and transgranular microcrack formation, leading to an intergranular brittle fracture. δ phase may assist the intergranular crack propagation, and this was shown to be particularly true when this phase is coarse enough to produce crack initiation, but this is not the only factor determining embrittlement. Other microstructural features play a role, as does the strength of the material. The aerospace heat treatment, which gives the highest strength and ductility in the uncharged state, shows the greatest reduction in properties with hydrogen charging.

Effect of hydrogen on the mechanical properties of alloy 945X (UNS N09945) and influence of microstructural features

This study investigated the hydrogen embrittlement sensitivity of the precipitation hardened (PH) alloy 945X in three different metallurgical states. The three variants examined (obtained by different heat treatments) were the standard oil and gas industry condition, and two alternative microstructures with variations in fraction and morphology of γ′, γ″ and δ phases. For each metallurgical state, mechanical tests were carried out on both uncharged and hydrogen pre-charged specimens in order to evaluate the deleterious influence of hydrogen on mechanical properties. Material characterisation and post-test fractography was performed to understand the link between microstructural features, fracture behaviour, and susceptibility to hydrogen embrittlement. Fractographic analysis showed that, in the presence of hydrogen, intergranular fracture occurred for all the heat treatments, regardless the presence of δ-phase at grain boundaries. There was no simple correlation between the volume fraction of δ-phase and susceptibility to hydrogen assisted embrittlement. Rather, it was demonstrated that the morphology and distribution of δ-phase along grain boundaries plays a key role and the other precipitate phases also have an influence through their influence on the ease of strain localization.

Finite Element Analysis of Hydrogen Transport in Steel Pressure Vessel at Room Temperature

Hydrogen embrittlement is commonly considered as an important failure mechanism for some typical steel pressure vessels and pipes made of such as Cr–Mo and 4130X steels at high-pressure hydrogen environment. In previous work, we investigated the hydrogen transport mechanisms of Crmo steel pressure vessels at room temperature. Furthermore, high temperature environment may affect the hydrogen transport mechanisms and hydrogen-induced crack behaviors in these structures to a large extent. In this paper, we study the hydrogen transport mechanisms in 2.25Cr–1Mo steel pressure vessel at high temperature under the support of National Key Fundamental Research and Development Project of China (2015.1-2019.12). The main work is to explore the effects of temperature, hydrogen concentration, and structural sizes on the transient hydrogen diffusion and distribution behaviors in Crmo steel pressure vessels using finite element analysis. Numerical results show that elevated high temperature accelerates the hydrogen embrittlement sensitivity, especially at structural discontinuities.

Influence of precipitation behavior on mechanical properties and hydrogen induced cracking during tempering of hot-rolled API steel for tubing

Precipitation behavior and its effect on hydrogen embrittlement during tempering process of hot-rolled API steel designed with 0.4wt% Cr and 0.25wt% Mo were investigated. The base steel was normalized and then tempered at 650°C for up to 60min. The precipitation behavior of the examined steel was explored using transmission electron microscopy (TEM) analysis, and it was found that the precipitation sequence during tempering at 650°C were as follows: MX+M3C→MX→MX+M7C3+M23C6. The change of particle fraction was measured by electrolytic extraction technique. At the early stage of tempering, the particle fraction greatly decreased due to dissolution of M3C particle, and increased after 10min by the precipitation of M7C3 and M23C6 particles. The particle fraction showed a peak at 30min tempering and decreased again due to the dissolution of M7C3 particle. Vickers hardness tests of base steel and tempered samples were carried out, and then the hardness was changed by accompanying with the change of particle fraction. The sensitivity of hydrogen embrittlement was evaluated through hydrogen induced cracking (HIC) tests, and the results clearly proved that HIC resistance of tempered samples was better than that of base steel due to the formation of tempered martensite, and then the HIC resistance changed depending on the precipitation behavior during tempering, i.e., the precipitation of coarse M23C6 and M7C3 particles deteriorated the HIC resistance.

Effects of deformation on the microstructures and mechanical properties of carbide–free bainitic steel for railway crossing and its hydrogen embrittlement characteristics

The effects of deformation on the microstructures and mechanical properties of carbide–free bainitic steel for railway crossing were studied in detail, with an aim of analyzing the hydrogen embrittlement characteristics of the deformed bainitic steel. A small deformation could cause a notable increase in the strength and a slash decrease in uniform plasticity. High density of dislocations accumulated during the deformation and the newly formed high strength martensite should be responsible for the changes of mechanical properties. Results from the slow strain rate tests reveal that the hydrogen embrittlement sensitivity is higher for the deformed bainitic steel as compared with the undeformed steel, which also increase with increasing reduction. It should be attributed to the newly formed martensite phase, the accumulated dislocations and the heterogeneous residual stress in the deformed specimens. Fractography observations reveal a changed fracture mode from ductile to brittle with increasing hydrogen charging time.

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Hydrogen embrittlement sensitivity of SAE9254 (tensile strength of 1.7 – 2.0 GPa class) and vanadium added spring steel (9254V) with a tensile strength of 2.0 GPa class was evaluated by conventional strain rate tensile tests (CSRT) and torsion strength tests, using smooth specimens respectively. In the CSRT evaluation, the maximum tensile stress of the both steels decreased with the increment of diffusible hydrogen content. On the other hand, in the torsion tests, the maximum shear stress hardly exhibited any decrease until the hydrogen content reached 6mass ppm, where the cracking trace changed from shear plane (transverse direction of the specimen) to a resolved tensile stress plane (45°against the shear plane); fractgraphically, from micro-void coalescence (MVC) to intergranular fracture, and the torsional strength began to decrease. The resistance to hydrogen embrittlement of the CSRT properties of 9254V was superior to that of vanadium-free SAE9254 in the equivalent tensile strength level. Although the superior performance for the latter steel attributes partially to the reduction of phosphorous and sulfur contents, it should be noted that the addition of vanadium contributes the refining of prior austenite grains followed by the reduced intergranular segregation of phosphorus and sulfur. The hydrogen trapping effect at the vanadium carbide interface may contribute too. However, there was no difference between SAE9254 and 9254V in hydrogen embrittlement sensitivity when the torsion test is conducted.