Effect of high-pressure hydrogen environment in elastic and plastic deformation regions on slow strain rate tensile tests for iron-based superalloy A286

To investigate the effects of a high-pressure hydrogen environment in the elastic and plastic deformation regions, we performed slow strain-rate tensile tests of iron-based superalloy A286 at 150 °C by switching the atmosphere from 70 MPa hydrogen to air during the tests. The relationship between the nominal strain exposed to a hydrogen environment and the relative reduction in area (RRA) revealed that in the plastic deformation region, the RRA value decreased gradually depending on the nominal strain exposed to hydrogen, but in the elastic deformation region, the RRA value decreased rapidly. The RRA value further decreased when the stress cycle was applid in the elastic region. The fracture surface exhibited an intragranular slip plane fracture similar to that of the hydrogen-charged specimen. These phenomena suggest that the lattice decohesion theory is dominant in the elastic region, where hydrogen embrittlement occurs owing to an increase in the content of dissolved hydrogen.     

Dependence of hydrogen embrittlement on hydrogen in the surface layer in type 304 stainless steel

Hydrogen embrittlement (HE) together with the hydrogen transport behavior in hydrogen-charged type 304 stainless steel was investigated by combined tension and outgassing experiments. The hydrogen release rate and HE of hydrogen-charged 304 specimens increase with the hydrogen pressure for hydrogen-charging (or hydrogen content) and almost no HE is observed below the hydrogen content of 8.5 mass ppm. Baking at 433 K for 48 h can eliminate HE of the hydrogen-charged 304 specimen, while removing the surface layer will restore HE, which indicates that hydrogen in the surface layer plays the primary role in HE. Scanning electron microscopy (SEM) and scanning tunnel microscopy (STM) observations show that particles attributed to the strain-induced α′ martensite formation break away from the matrix and the small holes form during deformation on the specimen surface. With increasing strain, the connection among small holes along {111} slip planes of austenite will cause crack initiation on the surface, and then the hydrogen induced crack propagates from the surface to interior.     

Simulation of the impact of internal pressure on the integrity of a hydrogen-charged Type-316L stainless steel during slow strain rate tensile test

A hydrogen-charged Type-316L austenitic stainless steel represents a slight loss of tensile ductility and cup-and-cone fracture accompanied by small-sized dimple. The reduction in the dimple size is interpreted to be attributed to void sheets caused by localized slip deformations by hydrogen. This paper aims to clarify the contribution of an internal pressure to the characteristic void growth of a hydrogen-charged Type-316L stainless steel during slow strain rate tensile (SSRT) test in air at room temperature. The internal pressure of pre-existing voids in the specimen charged by 100 MPa hydrogen gas at 270 °C for 200 h was simulated by diffusion-desorption analysis of hydrogen with the finite differential method (FDM). The subsequent impact of the internal pressure on the void growth was simulated by fracture-mechanics approach with the finite element method (FEM). The simulations performed under various void morphologies and fracture toughness suggested that the internal pressure in the voids was significantly low, hardly affecting the void growth.     

Effects of hydrogen pressure and prior austenite grain size on the hydrogen embrittlement characteristics of a press-hardened martensitic steel

The effects of hydrogen gas pressure and prior austenite grain size (PAGS) on the susceptibility of a 22MnB5 press-hardened martensitic steel (PHS) to hydrogen embrittlement were studied. The hydrogen test apparatus at NIST-Boulder was modified for tensile testing of plate-type and sheet-type specimens in gaseous hydrogen. This modification made it possible to evaluate the slow strain rate tensile (SSRT) properties of the PHS with three different PAGS at various hydrogen pressures (0.21 MPa–5.5 MPa). SSRT testing in gaseous hydrogen resulted in significant reductions of both the tensile strength and ductility, as compared to those measured in air. In addition, the presence of gaseous hydrogen resulted in a transition in fracture morphology from the near-45° slant fracture to a more brittle fracture along a plane perpendicular to the tensile axis. The hydrogen-affected fracture zones were connected to the sheet specimen free surfaces, signifying the effect of external hydrogen. The fracture surfaces of the hydrogen-embrittled specimens contained relatively flat, “cleavage-like” facets, the size of which depended on the PAGS or packet size. The PHS having the largest PAGS represented generally larger secondary cracks and straighter crack paths in addition to a greater area fraction of the “cleavage-like” facets, likely indicative of a lower frequency of crack deflections. Compared to the largest PAGS condition, the two PHS with smaller PAGS were more resistant to the hydrogen-induced fracture especially at relatively low hydrogen gas pressures (<0.52 MPa). In contrast, with an increase in hydrogen pressure, all PHS specimens exhibited significant decreases in tensile strength and ductility. The positive effect of refining martensitic microstructure, at the low hydrogen pressures, is likely associated with improved toughness of the smaller grain-sized specimens.     

Evaluation of the pressure dependence of the cycle durability and thermodynamics of a metal hydride compressor composed of ternary V40 and V70TiCr

In this study, the cycle durability and thermodynamic characteristics of V₄₀TiCr and V₇₀TiCr were examined to evaluate their performance as metal hydride compressors. The cycles of incomplete hydrogen absorption under low pressure increased the hysteresis in the higher hydrogen concentration region, wherein cycling was not conducted, thereby forming an unavailable region; however, the equilibrium absorption pressure recovered after several full cycles at higher pressure. Due to the thermodynamic evaluation after 300 full cycles, V₄₀TiCr with 0.70, 0.53, and 0.44 of Ti/Cr ratio are expected to compress 1.2 wt% of hydrogen from 0.25 to 4.9 MPa, 1.96–22.2 MPa, and 5.97–46.8 MPa, respectively, between 40 and 150 °C. V₇₀TiCr with a low Ti/Cr ratio (0.33) demonstrated good cycle durability and is expected to compress 1.7 wt% of hydrogen 10 times from 5.4 to 54.8 MPa between 35 and 155 °C.     

Hydrogen embrittlement of the coarse grain heat affected zone of a quenched and tempered 42CrMo4 steel

The coarse grain heat affected zone (CG-HAZ) of welds produced in a quenched and tempered 42CrMo4 steel was simulated by means of a laboratory heat treatment consisting in austenitizing at 1200 °C for 20 min, oil quenching and finally applying a post weld heat treatment at 700 °C for 2 h (similar to the tempering treatment previously applied to the base steel). A tempered martensite microstructure with a prior austenite grain size of 150 μm and a hardness of 230 HV, similar to the aforementioned CG-HAZ weld region, was produced. The effect of the prior austenite grain size on the hydrogen embrittlement (HE) behaviour of the steel was studied comparing this coarse-grained microstructure with that of the fine-grained base steel, with a prior austenite grain size of 20 μm.The specimens used in this study were charged with hydrogen gas in a reactor at 19.5 MPa and 450 °C for 21 h. Cylindrical specimens were used to determine hydrogen uptake and hydrogen desorption behaviour. Smooth and notched tensile specimens tested under different displacement rates were also used to evaluate HE.Embrittlement indexes, EI, were generally quite low in the case of hydrogen pre-charged tensile tests performed on smooth tensile specimens. However, very significant embrittlement indexes were obtained with notched tensile specimens. It was observed that these indexes always increase as the applied displacement rate decreases. Moreover, hydrogen embrittlement indexes also increase with increasing prior austenite grain size. In fact, the embrittlement index related to the reduction in area, EI_(RA), reached values of over 20% and 50% for the fine and coarse grain size steels, respectively, when tested under the lowest displacement rates (0.002 mm/min).A comprehensive fractographic analysis was performed and the main operative failure micromechanisms due to the presence of internal hydrogen were determined at different test displacement rates. While microvoids coalescence (MVC) was found to be the typical ductile failure micromechanism in the absence of hydrogen in the two steels, brittle decohesion mechanisms (carbide-matrix interface decohesion, CMD, and martensitic lath interface decohesion, MLD) were observed under internal hydrogen. Intergranular fracture (IG) was also found to be operative in the case of the coarse-grained steel tested under the lowest displacement rate, in which hydrogen accumulation in the process zone ahead of the notch tip is maximal.     

Biohydrogen production improvement using hot compressed water pretreatment on sake brewery waste

Most hydrogen is derived from fossil fuels. Therefore, more environmentally friendly methods for hydrogen production have been investigated. The present report describes a hot compressed water (HCW) pretreatment to increase hydrogen production using sake lees, which is an industrial waste of sake production. The inoculum is obtained from treated biogas slurry. The temperatures of HCW are 130 (0.3 MPa), 150 (0.5 MPa), and 180 °C (0.8 MPa) for 15–120 min. Gas production was analyzed using gas chromatography; fermentation liquid analyses were performed using HPLC. The modified Gompertz model was used to determine hydrogen potential, lag time, and production rate. Results show an increase in the degradation of sake lees with longer holding time and higher temperature. Total sugar and organic acids also are influenced by HCW pretreatment. The maximum hydrogen yield was obtained at 130 °C for 60 min with the result 112.07 mL H₂/g COD. The HCW pretreatment successfully decreased the lag phase of biohydrogen production and increased the degree of acidification. Clostridium butyricum, C. acetobutylicum, and other Clostridium sp. were identified in all samples, while Pantoea agglomerans was detected in two samples.     

Intercritical annealing temperature dependence of hydrogen embrittlement behavior of cold-rolled Al-containing medium-Mn steel

The present investigation attempts to evaluate the influence of intercritical annealing temperature (T_IA) on the hydrogen embrittlement (HE) of a cold-rolled Al-containing medium-Mn steel (Fe-0.2C-4.88Mn-3.11Al-0.62Si) by using electrochemical hydrogen-charging, slow strain rate tensile test and scanning electron microscope. The results show that an excellent combination of strength and ductility (the product of ultimate tensile strength and total elongation) up to ∼53 GPa·% was obtained for the specimen intercritically annealed at an intermediate temperature of 730 °C, whereas the HE index increases significantly with an increase in T_IA up to 850 °C. Being different from the typical dimple ductile fracture for the uncharged specimen, the hydrogen-charged specimen exhibits a mixed brittle interface decohesion and ductile intragranular fracture mode in the crack initiation region and the brittle fracture fraction increases with increasing T_IA. Both the stability and amount of austenite play a critical role in governing the HE behavior of TRIP-assisted medium-Mn steel. Thus, it is suggested that suitable T_IA should be explored to guarantee the safety service of automotive parts made of this type of steel in addition to acquiring excellent mechanical properties.     

Effect of strain-induced martensite on hydrogen embrittlement of austenitic stainless steels investigated by combined tension and hydrogen release methods

The hydrogen transport behavior together with hydrogen embrittlement (HE) in hydrogen-charged type 304 and 316 stainless steels during deformation was investigated by combined tension and outgassing experiments. The specimens were thermally hydrogen-charged in 30 MPa hydrogen at 473 K for 48 h. HE of hydrogen-charged type 304 steel decreases with increasing prestrain and almost no HE is observed in hydrogen-charged type 316 steel. Prior strain-induced α′ martensite formed by the prestrain at 208 K has little relation with HE, while dynamic α′ martensite formed during deformation after the prestrain shows obvious HE. The differences in hydrogen diffusivity and solubility between α′ martensite and austenite (γ) induce hydrogen diffusion from dynamic α′ martensite and then its accumulation at the boundary between the α′-rich and γ-rich zones, resulting in crack initiation at the boundary between the α′-rich and γ-rich zones.     

Hydrogen embrittlement of structural steels: Effect of the displacement rate on the fracture toughness of high-pressure hydrogen pre-charged samples

The aim of this paper is to study the effect of the displacement rate on the fracture toughness under internal hydrogen of two different structural steels grades used in energy applications. To this end, steel specimens were pre-charged with gaseous hydrogen at 19.5 MPa and 450 °C for 21 h and then fracture toughness tests were carried out in air at room temperature. Permeation experiments were also conducted to obtain the hydrogen diffusion coefficients of the steels. It was observed that the lower the displacement rate and the higher the steel yield strength, the stronger the reduction in fracture toughness due to the presence of internal hydrogen. A change in the fracture micromechanism was also detected. All these findings were justified in terms of hydrogen diffusion and accumulation in the crack front region in the different steel specimens.     

Low-temperature tensile and impact properties of hydrogen-charged high-manganese steel

Low-temperature mechanical properties of a high-manganese austenitic steel were evaluated with and without hydrogen pre-charging to examine the applicability of the alloy as a material for hydrogen infrastructure. The high-manganese steel, along with the conventional 304 and 316 L austenitic steels, was examined for hydrogen-related properties including hydrogen content after gas-phase pre-charging, tensile properties, and Charpy impact toughness at different temperatures ranging from room temperature to −80 and −196 °C, respectively, and the resultant fracture surfaces. Under hydrogen-charged conditions, the high-manganese steel showed low-temperature mechanical properties comparable to those of conventional austenitic steels, suggesting the potential of the alloy for structural applications in hydrogen environment.     

Demonstration of a single-stage metal hydride hydrogen compressor composed of BCC V40TiCr alloy

In this study, demonstration of a one-stage metal hydride hydrogen compressor (MH compressor) by using a BCC alloy was performed. It was estimated that V₄₀Ti₂₂Cr₃₈ could compress approximately 1.6 wt% of hydrogen from 1.0 to 10 MPa in 20–140 °C temperature range from equilibrium theory via pressure-composition-isotherm measurements. For demonstration of an actual MH compressor, a kg-scale experimental system was set up; V₄₀Ti₂₂Cr₃₈ (1.4 kg) was introduced into a 1-inch cylindrical vessel with a heat-medium flow tube outside. As a result, 1.0 MPa of hydrogen can be compressed into the hydrogen cylinder at >10 MPa by hydrogen absorption at 10 °C and desorption at 160 °C for 30 min each (1 cycle/h) to achieve a compression rate of 0.23 Nm³/h and indicate the potential of the practical MH compressors by using BCC alloy.     

Valorisation of vegetable market wastes to gas fuel via catalytic hydrothermal processing

Residues of leek, cabbage and cauliflower from the market places as representatives of lignocellulosic biomass were processed via hydrothermal gasification to produce energy fuel. The experiments were carried out in a batch reactor at temperatures 300, 400, 500 and 600 °C and corresponding pressures varying in the range of 7.5–43 MPa. Natural mineral additives trona, dolomite and borax were used as homogenous catalysts to determine their effects on the gasification. More than 70 wt% of carbon in vegetable residue samples were detected in the gas phase after the hydrothermal gasification process at 600 °C. The addition of trona mineral further promoted the gasification reactions and as a result, less than 5 wt% carbon remained in the solid residue at the same temperature, degrading the biomass samples into gas and liquid products. The fuel gas with the highest calorific value was recorded to be 25.6 MJ/Nm³, from the hydrothermal gasification of cabbage at 600 °C, when dolomite was used as the homogeneous catalyst. The liquid products obtained in the aqueous phase were detected as organic acids, aldehydes, ketones, furfurals and phenols. The gas products were consisted of hydrogen, carbon dioxide, methane, and as minors; carbon monoxide and low molecular weight hydrocarbons (ethane, propane, etc.). Above 500 °C, all biomass samples yielded 50–55 vol% of CH₄ and H₂ while the CO₂ composition was around 40 vol% as the gas product.     

The dependence of fatigue crack growth on hydrogen in warm-rolled 316 austenitic stainless steel

The fatigue crack growth rate of warm-rolled AISI 316 austenitic stainless steel was investigated by controlling rolling strain and temperature in argon and hydrogen gas atmospheres. The fatigue crack growth rates of warm-rolled 316 specimens tested in hydrogen decreased with increasing rolling temperature, especially 400 °C. By controlling the deformation temperature and strain, the influences of microstructure (including dislocation structure, deformation twins and α′ martensite) and its evolution on hydrogen-induced degradation of mechanical properties were separately discussed. Deformation twins deceased and dislocations became more uniform with the increase in rolling temperature, inhibiting the formation of dynamic α′ martensite during the crack propagation. In the cold-rolled 316 specimens, deformation twins accelerated hydrogen-induced crack growth due to the α′ martensitic transformation at the crack tip. In the warm-rolled specimens, the formation of α′ martensite around the crack tip was completely inhibited, which greatly reduced the fatigue crack growth rate in hydrogen atmosphere.     

Effects of stress concentration on the mechanical properties of X70 in high-pressure hydrogen-containing gas mixtures

This study aims to investigate the mechanical properties of X70 pipeline steel under the synergistic influence of hydrogen and stress concentration. Slow strain rate tensile tests and low-cycle fatigue tests were performed on the specimens with different stress concentration factors (Kt) in 10 MPa nitrogen/hydrogen mixtures. Results show that the degradation degree of the ductility and fatigue life of X70 steel induced by hydrogen increases with the increase of Kt, and as the hydrogen partial pressure in mixtures increases, the influence of Kt on hydrogen-induced degradation increases as well. In addition, finite element analysis was performed via a modified hydrogen diffusion/plasticity coupled model to study the effect of Kt on hydrogen distribution in the specimens, which can influence the mechanical properties of X70. The maximum hydrogen concentration consistently appears at the notch tip of the specimen and increases with the increase of Kt, which is proposed to be one of the reasons for the severe hydrogen embrittlement of the specimens with large Kt. As the axial tensile force on the specimen increases, the maximum hydrogen concentration at the notch tip begins to be dominated by hydrogen in the normal interstitial lattice sites and, subsequently, in the trapping sites.     

Cold-rolled magnesium hydride strips decorated with cold-sprayed Ni powders for solid-state-hydrogen storage

The present work reports for the first time application of cold spray coating for doping plastically deformed Mg-strips by different concentrations of fine Ni powders. For present study, Mg rods were cold-rolled for 300 passes and then coated by Ni fine powders, using a cold spray process operated at 150 °C under high argon gas pressure. The Ni powders were pelted into Mg-substrate through the high-velocity jet at a speed of 500 m/s. Under these preparation conditions, Ni powders were plastically deformed at the surface of Mg strips to create numerous pores and cavities, worked as hydrogen diffusion gateway. The as-coated Mg sheets with 3-Ni layers (5.28 wt%) possessed good hydrogenation/dehydrogenation kinetics, implied by a short absorption/desorption time (5.1/11 min) of 6.1 wt% hydrogen at 150 °C/10 bar and 200 °C/200 mbar, respectively. The fabricated solid-state hydrogen storage nanocomposite strips revealed good cyclability of achieving 600 cycles at 200 °C without failure of degradation.     

Damage associated with interactions between microstructural characteristics and hydrogen/methane gas mixtures of pipeline steels

There is no common standard for blended hydrogen use in the natural gas grid; hydrogen content is generally based on delivery systems and end-use applications. The need for a quantitative evaluation of hydrogen-natural gas mixtures related to the mechanical performance of materials is becoming increasingly evident to obtain long lifetime, safe, and reliable pipeline structures. This study attempts to provide experimental data on the effect of H₂ concentration in a methane/hydrogen (CH₄/H₂) gas mixture used in hydrogen transportation. The mechanical performance under various blended hydrogen concentrations was compared for three pipeline steels, API X42, X65, and X70. X65 exhibited the highest risk of hydrogen-assisted crack initiation in the CH₄/H₂ gas mixture in which brittle fractures were observed even at 1% H₂. The X42 and X70 samples exhibited a significant change in their fracture mechanism in a 30% H₂ gas mixture condition; however, their ductility remained unchanged. There was an insignificant difference in the hydrogen embrittlement indices of the three steels under 10 MPa of hydrogen gas. The coexistence of delamination along with the ferrite/pearlite interface, heterogeneous deformation in the radial direction, and abundance of nonmetallic MnS inclusions in the X65 sample may induce a high stress triaxiality at the gauge length at the beginning of the slow strain rate tensile process, thereby facilitating efficient hydrogen diffusion.     

Hydrogen embrittlement and associated surface crack growth in fine-grained equiatomic CoCrFeMnNi high-entropy alloys with different annealing temperatures evaluated by tensile testing under in situ hydrogen charging

The effect of the annealing temperature after cold rolling on hydrogen embrittlement resistance was investigated with a face-centered cubic (FCC) equiatomic CoCrFeMnNi high-entropy alloy using tensile testing under electrochemical hydrogen charging. Decreasing annealing temperature from 800 °C to 750 °C decreased grain sizes from 3.2 to 2.1 μm, and resulted in the σ phase formation. Interestingly, the specimen annealed at 800 °C, which had coarser grains, showed a lower hydrogen embrittlement susceptibility than the specimen annealed at 750 °C, although hydrogen-assisted intergranular fracture was observed in both annealing conditions. Because the interface between the FCC matrix and σ was more susceptible to hydrogen than the grain boundary, the presence of the matrix/σ interface significantly assisted hydrogen-induced mechanical degradation. In terms of intergranular cracking, crack growth occurred via small crack initiation near a larger crack tip and subsequent crack coalescence, which has been observed in various steels and FCC alloys that contained hydrogen.     

Effects of hydrogen on the fracture toughness of CrMo and CrMoV steels quenched and tempered at different temperatures

Tempering temperatures ranging between 500 and 720 °C were applied in order to analyse the relationship between steel microstructure and the deleterious effect of hydrogen on the fracture toughness of different CrMo and CrMoV steels. The influence of hydrogen on the fracture behaviour of the steel was investigated by means of fracture toughness tests using CT specimens thermally pre-charged with hydrogen gas.First, the specimens were pre-charged with gaseous hydrogen in a pressurized reactor at 19.5 MPa and 450 °C for 21h and elasto-plastic fracture toughness tests were performed under different displacement rates. The amount of hydrogen accumulated in the steel was subsequently determined in order to justify the fracture toughness results obtained with the different steel grades. Finally, scanning electron microscopy was employed to study both the resulting steel microstructures and the fracture micromechanisms that took place during the fracture tests.According to the results, hydrogen solubility was seen to decrease with increasing tempering temperature, due to the fact that hydrogen microstructural trapping is lower in relaxed martensitic microstructures, the strong effect of the presence of vanadium carbides also being noted in this same respect. Hydrogen embrittlement was also found to be much greater in the grades tempered at the lowest temperatures (with higher yield strength). Moreover, a change in the fracture micromechanism, from ductile (microvoid coalescence, MVC), in the absence of hydrogen, to intermediate (plasticity-related hydrogen induced cracking, PRHIC) and brittle (intergranular fracture, IG), was appreciated with the increase in the embrittlement indexes.     

Hydrogen production enhancement using hot gas cleaning system combined with prepared Ni-based catalyst in biomass gasification

This paper investigates the hot gas temperature effect on enhancing hydrogen generation and minimizing tar yield using zeolite and prepared Ni-based catalysts in rice straw gasification. Results obtained from this work have shown that increasing hot gas temperature and applying catalysts can enhance energy yield efficiency. When zeolite catalyst and hot gas temperature were adjusted from 250 °C to 400 °C, H₂ and CO increased slightly from 7.31% to 14.57%–8.03% and 17.34%, respectively. The tar removal efficiency varies in the 70%–90% range. When the zeolite was replaced with prepared Ni-based catalysts and hot gas cleaning (HGC) operated at 250 °C, H₂ contents were significantly increased from 6.63% to 12.24% resulting in decreasing the hydrocarbon (tar), and methane content. This implied that NiO could promote the water-gas shift reaction and CH₄ reforming reaction. Under other conditions in which the hot gas temperature was 400 °C, deactivated effects on prepared Ni-based catalyst were observed for inhibiting syngas and tar reduction in the HGC system. The prepared Ni-based catalyst worked at 250 °C demonstrate higher stability, catalyst activity, and less coke decomposition in dry reforming. In summary, the optimum catalytic performance in syngas production and tar elimination was achieved when the catalytic temperature was 250 °C in the presence of prepared Ni-based catalysts, producing 5.92 MJ/kg of lower heating value (LHV) and 73.9% tar removal efficiency.