Hydrogen Charging Current Density Research Articles

Characterization of hydrogen embrittlement sensitivity of 18CrNiMo7-6 alloy steel surface-modified layer based on scratch method

PurposeThe purpose of this paper is to assess the hydrogen embrittlement sensitivity of carbon gradient heterostructure materials and to verify the reliability of the scratch method.Design/methodology/approachThe surface-modified layer of 18CrNiMo7-6 alloy steel was delaminated to study its hydrogen embrittlement characteristics via hydrogen permeation, electrochemical hydrogen charging and scratch experiments.FindingsThe results showed that the diffusion coefficients of hydrogen in the surface and matrix layers are 3.28 × 10−7 and 16.67 × 10−7 cm2/s, respectively. The diffusible-hydrogen concentration of the material increases with increasing hydrogen-charging current density. For a given hydrogen-charging current density, the diffusible-hydrogen concentration gradually decreases with increasing depth in the surface-modified layer. Fracture toughness decreases with increasing diffusible-hydrogen concentration, so the susceptibility to hydrogen embrittlement decreases with increasing depth in the surface-modified layer.Originality/valueThe reliability of the scratch method in evaluating the fracture toughness of the surface-modified layer material is verified. An empirical formula is given for fracture toughness as a function of diffused-hydrogen concentration.

Hydrogen-assisted fatigue crack propagation behavior of a C–N co-doped interstitial high-entropy alloy

The hydrogen-assisted fatigue crack propagation behavior of a C–N co-doped interstitial high-entropy alloy (iHEA) was investigated under in-situ electrochemical hydrogen charging. The cracking path, deformation microstructure, and fractography were characterized via multiple methods. Results suggest that hydrogen uptake shows a certain acceleration on the fatigue crack propagation rate (FCGR) of the iHEA, and such acceleration increases are intensified when increasing the hydrogen-charging current density. Crack propagation along grain boundaries and a remarkable decrease in the extent of plastic deformation immediately near to the crack surface have also been observed. This decrement of critical plastic strain for fatigue crack propagation primarily accelerates the FCGR.

Effects of hydrogen charge on the intergranular corrosion of high-defect-density ultrapure ferrite stainless steel

This research scrutinizes the intricate effects of hydrogen charging on crystal defects and passive film properties in high-defect-density 443 ultrapure ferritic stainless steel. It discerns that with non-saturated hydrogen at hydrogen traps, escalated hydrogen charging current density results in increased hydrogen capture. These trapped atoms fill the defects, thus mitigating the stress level and fostering the growth of chromium oxides within the passive film. Consequently, the alloy’s resistance to intergranular corrosion is enhanced.

Effect of Electrochemical Hydrogen Charging on Blistering and Mechanical Properties Behavior of Q690 Steel

The purpose of this work is to study the effect of charging conditions on hydrogen damage. The effects of electrochemical hydrogen charging current density and time on hydrogen-induced blistering (HIB), cracking behavior, and mechanical properties of Q690 steel are studied by electrochemical hydrogen charging, microstructure observation, and slow strain rate tensile (SSRT) tests. The results show that HIB and internal cracks occur when the Q690 steel is charged at different current densities. The charging conditions have a significant effect on the HIB characteristics of the material and the morphology, number, size, and location of internal cracks. The geometrical parameters of blisters on the surface of Q690 steel are quantitatively evaluated, and deeper cracks are found at higher hydrogen concentrations. At high hydrogen charging current density (50 mA/cm2), due to the accumulation of a large number of hydrogen atoms and the precipitation of hydrogen, the active sites on Q690 steel surface increase dramatically, leading to the initiation of a large number of blisters. At this time, high current density is responsible for the initiation of blisters. The relationship between hydrogen charging current density and mechanical properties of Q690 steel is studied, and the change in the fracture morphology is observed. The Q690 steel was damaged and failed due to an internal crack caused by excessive hydrogen pressure. On the other hand, electrochemical hydrogen charging leads to the degradation of mechanical properties and the transition from ductile fracture to brittle fracture.

The compact-strip-produced martensitic steel possessing better resistance to hydrogen-induced delayed cracking

Hydrogen-induced delayed cracking (HIDC) of martensitic steel limits its extensive application in lightweight automobile industry. Up to now, the research regarding HIDC of compact-strip-produced martensitic steel (CSP-MS) has not been reported. The HIDC behavior of CSP-MS steel was investigated. It was found that with the increase of hydrogen-charging current density in slow strain rate tensile tests, tensile strength of the two martensitic steels is relatively similar, however elongation decreases significantly while hydrogen embrittlement index (IHE) increases dramatically. The IHE of CSP-MS steel is lower than that of conventional produced martensitic steel (Con-MS) under all test conditions, as indicating that CSP-MS steel has better resistance to HIDC. The small size of TiN in CSP-MS steel leads to delayed initiation of microcrack than that of Con-MS steel, which is the mechanism for its superior resistance to HIDC. This work provides a new avenue for large-scale application of martensitic steel in automotive industry.

Research on hydrogen permeation in the X80 steel heat-affected zone with different heat inputs

Through electrochemical hydrogen permeation experiment at different hydrogen charging current densities, the hydrogen diffusion kinetic parameters such as penetration time tB , steady-state hydrogen permeation current density I ∞, hydrogen diffusion coefficient D, adsorbed hydrogen concentration C 0, hydrogen flux J, and hydrogen trap density NT in the heat-affected zone of X80 steel welding with different heat input were analyzed. The results show that the penetration time gradually decreases, and the I ∞ gradually increases with the increase of hydrogen charging current density. The penetration time of BM at the same hydrogen charging current density is the smallest, and the penetration times of CGHAZ specimens with different heat input conditions are relatively close. BM has the most significant hydrogen diffusion coefficient and negligible hydrogen trap density at the same hydrogen charging current densities. For CGHAZ, D significantly decreases and NT substantially increases, and there exists a threshold value that makes the lowest D in the CGHAZ with different heat inputs.

Interaction between dislocations, precipitates and hydrogen atoms in a 2000 MPa grade hot-stamped steel

Inhibiting the diffusion and aggregation of hydrogen atoms can effectively improve the resistance to hydrogen embrittlement (HE) of high strength hot-stamped steel. Here we investigate the interaction between dislocations, precipitates and hydrogen atoms in a 2000 MPa grade hot-stamped steel through a combination of microstructure characterization and HE sensitivity tests. Results show that HE susceptibility indexes increase with the increase of hydrogen charging current density, and the corresponding HE mechanism transfers from hydrogen-enhanced localized plasticity (HELP) dominates to hydrogen-enhanced decohesion (HEDE) dominates. Additionally, dislocations as reversible hydrogen traps with an activation energy of 36.3 kJ/mol, and through calculation, dislocations can carry hydrogen atoms to move. Moreover, we find that dispersed V-rich (Ti, V)C precipitates can refine grain to increase the number of reversible hydrogen traps, pin dislocations to inhibit H–dislocation interaction, and act as irreversible hydrogen traps to capture hydrogen atoms and, consequently, raise the resistance to HE.

Effect of Hydrogen Charging on the Stress Corrosion Cracking Behavior of X70 Steel in Simulated Deep Seawater Environment

The effects of hydrogen charging on the electrochemical and stress corrosion cracking (SCC) behavior of X70 steel in a simulated deep seawater environment were investigated by using electrochemical measurements, slow strain rate tensile (SSRT) tests, and corrosion morphology characterization through SEM. The results showed that the concentrations of the adsorbed hydrogen in X70 steel after precharging under different hydrostatic pressures increased gradually and tended to be steady with the charging time. High hydrostatic pressures promoted the hydrogen permeation of X70 pipeline steel by promoting the permeating rate and quantity. The SCC susceptibility of X70 steel decreased first and then increased with the hydrogen-charging current density. The area reduction loss (Iψ) and true strain loss (Iε) exhibited the lowest SCC susceptibility at the 25 mA/cm2 hydrogen-precharging current density. The elongation rate loss (Iδ) exhibited the lowest SCC susceptibility at the 50 mA/cm2 hydrogen-precharging current density.

Effect of cyclic plastic deformation on hydrogen diffusion behavior and embrittlement susceptibility of reeling-pipeline steel weldments

The hydrogen embrittlement (HE) susceptibility and hydrogen permeation behavior of reeling-pipeline welded joint with/without cyclic plastic deformation (CPD) were studied using the electrochemical hydrogen charging technique. Results indicated that the surface of welded joint emerged hydrogen-induced damage containing cracks and blisters. The degree of hydrogen-induced damage increased with the increase of hydrogen charging time and current density. When the hydrogen charging current density and time was 50 mA/cm2 and 4 h, respectively, the area ratio of hydrogen-induced damage of overall welded joint with CPD process was reduced from 6.61% to 2.28%, and the damage ratio of different sub-zones in welded joint was also decreased. The oxidized inclusions enriching Al–Mg–Ca elements acted as the initiation sites for hydrogen-induced damages. The effective diffusion coefficient of as-welded joint was 2.63 × 10−6 cm2/s, while that of welded joint with CPD showed a smaller value of 1.36 × 10−6 cm2/s. The welded joint with CPD process presented better resistance to HE, which was attributed to the increased density of hydrogen traps and the formation of dislocation cells to disperse hydrogen uniformly and reduce the possibility of local accumulation and recombination of diffusible hydrogen. Sub-zones in welded joint without CPD process were considerably more sensitive to hydrogen-induced damage, which indicated the important role of microstructure and dislocation density in HE mechanisms. The order of HE susceptibility from low to high was weld metal, base metal and heat affected zone.

Limiting Current Density of Oxygen Reduction under Ultrathin Electrolyte Layers: From the Micrometer Range to Monolayers

AbstractThe oxygen reduction reaction (ORR) under ultrathin electrolyte layers is a key reaction in many processes, from atmospheric corrosion to energy conversion in fuel cells. However, the ORR current under ultrathin electrolyte layers is difficult to measure using conventional electrochemical methods. Hence, reliable data are scarce for the micrometer range and totally missing for the sub‐micrometer range of the electrolyte layer thickness. Here, we report a novel hydrogen‐permeation‐based approach to measure the ORR current underneath thin and ultrathin electrolyte layers. By using a Kelvin‐probe‐based measurement of the potential, which results from dynamic equilibrium of oxygen reduction and hydrogen oxidation, and the corresponding hydrogen charging current density, the full current‐potential relationship can be constructed. The results shed a new light on the nature of the limiting current density of ORR underneath ultrathin layers of electrolyte.

The mutual effect of hydrogen and cyclic plastic deformation on ductility degradation of X65 reeled-pipeline welded joint

The safe service of reeled-pipeline welded joint subjected to multiple cyclic plastic deformation (CPD) is challenged by hydrogen embrittlement (HE) in the process of gas and petroleum transportation. Therefore, this work aims to study the interrelation of hydrogen and the ductility of X65 reeled-pipeline welded joint with CPD by using electrochemical hydrogen charging. The results showed that hydrogen could lead to the ductility degradation, regardless of whether the CPD process was performed. But the hydrogen-induced ductility degradation for the welded joint with CPD was retarded. When the hydrogen-charging current density was 50 mA/cm2, the hydrogen embrittlement index (IUE) based on the uniform elongation for welded joint with CPD was 0.33, while that of as-welded joint was 0.53, which indicated that CPD process reduced the sensitivity to HE. The morphology of tensile fracture indicated that brittle cracks initiated at the composite oxide inclusion enriched Al–Mg–Ca–S elements, and propagated radially by quasi-cleavage fracture pattern. The CPD process led to the increase of dislocations acting as reversible hydrogen traps, which significantly enhanced the hydrogen content of welded joint from 1.001 ppm to 2.516 ppm. However, the dislocation walls and cells related to the CPD process hindered the diffusion of hydrogen, and homogeneous distribution of dislocations after CPD dispersed trap sites for capturing hydrogen, which played important roles in delaying hydrogen-induced fracture.

Hydrogen embrittlement behavior of high strength low carbon medium manganese steel under different heat treatments

Hydrogen embrittlement (HE) behavior was investigated in a low carbon medium Mn steel with three different volume fraction of retained austenite (RA), which was obtained after different heat treatments. The hydrogen permeation test showed a higher permeability for directly water quenched specimen compared to quench-tempered specimens. Melt extraction test showed hydrogen concentration increased with hydrogen charging current density in the order of directly quenched specimen, QLA, quenched with low-temperature annealed specimens and QHA quenched with high-temperature annealed specimens. Slow strain-rate tensile test was employed to examine the HE behavior, the HE indices decreased with the increase of RA irrespective of increased hydrogen concentration. HE susceptibility can be suppressed by raising intercritical annealing temperature because Mn enrichment increases the stability of RA.

Effect of CrxCy–NiCr coating on the hydrogen embrittlement of 17-4 PH stainless steel using the smooth bar tensile test

A CrxCy–NiCr cermet coating was fabricated using the supersonic plasma spray technique, and its effect on the hydrogen embrittlement of 17-4 PH stainless steel was studied through electrochemical hydrogen charging and slow strain rate tensile testing. The index of hydrogen embrittlement susceptibility was calculated, and the results show that the CrxCy–NiCr coating plays a significant role in preventing hydrogen embrittlement cracking. The hydrogen content analysis demonstrates that the CrxCy–NiCr coating enhances the resistance to hydrogen embrittlement by acting as a hydrogen diffusion barrier. This effect is mainly due to the CrxCy ceramics in the cermet coating having a very low hydrogen diffusion rate. In addition, the strength and ductility of the specimen without the coating decrease gradually with increasing hydrogen charging current density. According to the tensile testing results and the fracture surface analysis, the hydrogen embrittlement phenomenon is explained by a mixed mechanism involving hydrogen-enhanced local plasticity and hydrogen-enhanced decohesion.

An Evaluation Method for Hydrogen Embrittlement of High Strength Steel Sheets Using U-bend Specimens

An evaluate method for hydrogen embrittlement property of high strength steel sheet has been proposed in this study. To take into consideration of the effect of plastic strain in addition to the effects of applied/residual stress and diffusible hydrogen, U-bend specimens have been adopted because steel sheets for automobiles are usually used after press forming into various parts. After U-shape bending, the specimen was loaded using a bolt. The proposed evaluation method is based on the measurement of critical hydrogen content or critical hydrogen charging condition for hydrogen embrittlement fracture at given stress and strain conditions. The hydrogen charging current density was increased in step-wise manner until cracking was observed, and cracking was detected by optical observation and by monitoring voltage between the sample and a counter electrode. The critical hydrogen contents for specimens with varied applied stress were obtained by means of thermal desorption spectroscopy. For the critical hydrogen content, both the hydrogen contents in strained portion of the specimen and no-strained portion were measured. The former is affected by introduced dislocations caused by straining and the latter is thought to be proportional to the hydrogen fugacity. Both critical hydrogen contents tended to be decreased slightly when the applied stress was relatively high.

Effect of hydrogen on the fracture toughness of X65 high-frequency welded pipeline

The effect of hydrogen on the fracture toughness of X65 high-frequency welded (HFW) pipelines was investigated both in a hydrogen environment and in air. The hydrogen environment was created by in situ hydrogen charging, using a simulated soil solution as the electrolyte. Four current densities were used, namely 1, 2, 4, and 8 mA/cm2. The fracture toughness was characterized by the crack tip opening displacement (CTOD). The CTOD values of the base metal and weld metal decreased with increasing hydrogen charging current density, and a higher reduction was seen in the weld metal. In addition, the hydrogen permeation and electron backscattered diffraction (EBSD) measurements were also applied to the base metal and weld metal to evaluate the hydrogen-induced cracking (HIC) susceptibility. The results showed that the weld metal had a higher HIC susceptibility than that of the base metal.

A study on stress corrosion cracking and hydrogen embrittlement of Jethete M152 martensitic stainless steel

Stress corrosion cracking and hydrogen embrittlement of Jethete M152 martensitic stainless steel were investigated by using constant load and slow strain rate tension test, optical microscope, transmission electron microscope and scanning electron microscope. The results show that lath martensite was formed and no austenite was observed. Stress corrosion cracking and hydrogen embrittlement were intensified with enhancing stress level and increasing hydrogen charging current density. Fractographic analysis revealed that corrosive environment resulted in the distinct change of fracture morphology from dimple to intergranular. It is indicated that undeformable Al2O3 inclusion is an important factor in stress corrosion cracking and hydrogen embrittlement for Jethete M152 steel. Meanwhile, it is beneficial to enhance resistance to stress corrosion cracking and hydrogen embrittlement by decreasing the inclusion size.

Hydrogen embrittlement behavior of Inconel 718 alloy at room temperature

Hydrogen embrittlement of Inconel 718 alloy was investigated. Multi-scale observation technique were employed, comprising slow strain rate tensile tests, scanning electron microscopy and transmission electron microscopy analysis. The results demonstrate that hydrogen charging deteriorates mechanical properties of the alloy. Inconel 718 alloy shows partial Portevin-Le Chatelier (PLC) effect at room temperature when hydrogen charging current density is 220 mA cm−2 and 590 mA cm−2. Moreover, plastic deformation features with dislocation cells are detected in hydrogen-induced brittle zone. Thus, it is concluded that dragging effect of hydrogen atoms on dislocations contributes to PLC effect.

Effect of Hydrogen Charging Conditions on Hydrogen Blisters and Pitting Susceptibility of 445J1M Ferritic Stainless Steel

The surface morphology and pitting susceptibility of 445J1M ferritic stainless steel in a NaCl solution before and after hydrogen charging were investigated using the atomic force microscope, X-ray photoelectron spectroscopy (XPS), potentiodynamic polarization, critical pitting temperature and the electrochemical impedance spectroscopy measurements. The content of hydrogen in 445J1M stainless steel increased from 1.7 ppm to 4.8 ppm with increasing the hydrogen-charging current density from 0 mA/cm2 (uncharged) to 25 mA/cm2. Hydrogen charging has induced blisters on the sample surface but not caused significant changes in the surface roughness. The size of hydrogen blisters on the samples increased with the rise of hydrogen charging current density. No direct connection could be found between the locations of hydrogen blisters and pitting nucleation. The pitting susceptibility and the instability of passive films both increased with the hydrogen-charging current density as shown by the electrochemical and XPS results. The breakdown potential decreased significantly with the increase of hydrogen-charging current density, accompanied by an increased passive current density. The decreased content of metal oxides in the passive films and the additional hydrogen oxidation reactions related to the permeated hydrogen can account for the deteriorated corrosion performance of the 445J1M ferritic stainless steel after hydrogen charging.

Failure mechanism transition of hydrogen embrittlement in AISI 304 K-TIG weld metal under tensile loading

The effect of hydrogen on the tensile properties of AISI 304 K-TIG weld metal is investigated in this study. Fractographic analysis demonstrates a transition from quasi-cleavage/cleavage fracture to intergranular fracture in the brittle zone as the hydrogen-charging current density increases, which is attributed to the interplay of crystalline defect, hydrogen atoms, and α′ martensite transformation sites. It is believed that at low current density, α′ martensite nucleates and grows homogeneously in the interior of the grain. At high current density, the stress-induced α′ martensite forms preferentially at the grain boundary, which undergoes severe strain localisation and hydrogen atom segregation.

Effect of pH and hydrogen on the stress corrosion cracking behavior of duplex stainless steel in marine atmosphere environment

Electrochemical and stress corrosion cracking (SCC) behaviors of 2205 duplex stainless steel (DSS) of different microstructures in the marine atmosphere environment with various pH values and hydrogen charging current densities were investigated by employing electrochemical measurements and the slow strain rate tensile (SSRT) method. Results indicated that the resistance of 2205 DSS to pitting corrosion deteriorated as the pH decreased, and the susceptibility to SCC improved in spite of the decrease in pH or the increase in hydrogen charging current density. As compared to the microstructure of the as-received specimen, microstructures of the normalized and especially the quenched samples were more vulnerable to SCC.