Hydrogen-assisted Cracking Research Articles

Influence of Preheating and Post Heating on Diffusible Hydrogen Content, Residual Stresses and Hydrogen Assisted Cracking (HAC) Susceptibility of Induction Assisted Gas Metal Arc Welded P91 Steel Joint

Influence of Preheating and Post Heating on Diffusible Hydrogen Content, Residual Stresses and Hydrogen Assisted Cracking (HAC) Susceptibility of Induction Assisted Gas Metal Arc Welded P91 Steel Joint

Experimental and crystal plasticity study on hydrogen-assisted fatigue crack growth behavior of IN625 superalloy

The fatigue crack growth (FCG) behavior of IN625 alloy was studied by experimental methods and crystal plasticity simulations. Based on the experimental FCG rate curves, it is evident that hydrogen significantly accelerates FCG, and calculations show that this acceleration factor reaches a maximum of 2.41 times at 1 Hz. Hydrogen results in smaller plastic deformation zones compared to hydrogen-free samples. The interaction between hydrogen and dislocations leads to the nucleation of micro-voids along the slip planes, promoting the hydrogen-assisted cracking process. Lower loading frequencies results in finer fatigue striations and more pronounced hydrogen embrittlement features on the fracture surface.

A new understanding of hydrogen-assisted cracking of coarse-grained heat-affected zone in X65 pipeline steel through {110} lath bainite boundary texture

The susceptibility of subzones of the coarse-grained heat-affected zone (CGHAZ) in X65 pipeline steel to hydrogen embrittlement was studied through an in situ crack-tip opening displacement test in an H2S-containing environment. The intercritically reheated CGHAZ (IC-CGHAZ) exhibited the highest embrittlement factor of 89.4%, compared to 64.0% for the sub-critically reheated CGHAZ (SC-CGHAZ). Hydrogen transportation by dislocations to massive-slender martensite/austenite (M/A) constituents initiated cracks in IC-CGHAZ. Deterioration of lath bainite (LB) boundaries, with separation of M/A-ferrite interface, accelerated crack propagation across prior austenite grains and promoted hydrogen-assisted degradation of fracture toughness. Reheated CGHAZ at a peak temperature of 620 °C led to an increased intensity of the {110} LB boundary texture by up to 52% in SC-CGHAZ. This enhanced texture facilitated dislocation slipping along {110} LB boundary planes, thereby promoting deformation compatibility and preventing the deterioration of LB boundaries in the presence of hydrogen.

Investigating variations in hydrogen-assisted crack propagation of X52 pipeline steel with different microstructural characteristics

In this study, the fracture behavior of two X52 pipeline steels with different microstructures in gaseous hydrogen environments was investigated. Specimen with polygonal ferrite and spheroidal pearlite exhibited reduced crack propagation resistance and brittle morphology in hydrogen gas, with crack selectively propagating along specific low-index planes (such as {001} and {011}). Conversely, specimen with acicular ferrite and spheroidal pearlite maintained ductile fracture behavior in hydrogen gas, characterized by crack blunting. The possible mechanisms of hydrogen-induced fracture toughness degradation were discussed in relation to grain boundary configuration and hydrogen content.

High-temperature fracture behavior of an α/β Titanium alloy manufactured using laser powder bed fusion

The room and high temperature (up to 600 °C) mechanical properties, with emphasis on the fracture toughness and fatigue resistance, of an α/β titanium alloy that was additively manufactured using the laser powder bed fusion (LPBF) technique were evaluated in the as-printed (α’ lath martensite with negligible β phase content) and heat-treated (α/β structure with a significant volume fraction of the β phase) states for critically examining the β phase's role in the fracture and fatigue behavior (given the significantly higher diffusion rates of various species in β compared to α). Experimental results reveal that the heat-treated sample exhibits superior ductility and fracture initiation toughness at elevated temperatures, compared to the as-printed sample, due to the presence of β ligaments in the former. They also prevent strain localization along the prior β grain boundaries, and their absence in the as-printed state leads to cracking along those boundaries. While the fatigue crack growth (FCG) rates in both the as-printed and heat-treated samples deteriorated with increasing temperature, the threshold for FCG generally increased, which is attributed to creep-induced crack tip blunting. Moreover, a double Paris exponent phenomenon is observed for the heat-treated sample at 300 °C, attributed to the hydrogen-assisted crack growth, with β phase providing an accelerated diffusion pathway. Overall, the experimental results and their analyses illustrate the intricate relationship between creep, hydrogen diffusion, and the β phase in dictating the fracture behavior of LPBF α/β titanium at elevated temperatures.

Role of slip in hydrogen-assisted crack initiation in Ni-based alloy 725.

We conduct in situ tensile straining experiments to investigate the role of hydrogen and slip in crack initiation in nickel-based alloy 725. Our experiments reveal no tendency for hydrogen to enhance localized slip and no necessity of slip for crack initiation. We use electrochemical charging to introduce hydrogen into samples, melt extraction to measure hydrogen content, and digital image correlation to analyze localized plastic strains during in situ tensile tests in a scanning electron microscope. Cracks initiate both in regions with and without nearby localized slip. Moreover, the fraction of cracks initiating with no nearby slip is greater at higher hydrogen content. Slip-assisted crack initiation generally occurs at locations where intergranular slip is arrested, especially at intersections of slipping coherent twin boundaries with thin twin lamellae. Cracks that initiate without nearby slip occur at a wider variety of microstructural features, including inclusions, triple junctions, and surface flaws.

In situ investigation of hydrogen embrittlement induced by δ phase in selective laser-melted GH4169 superalloy

Direct evidence of hydrogen-assisted crack nucleation and propagation associated with the δ phase in the selective laser melted GH4169 superalloy was obtained. The analysis of hydrogen trapping sites using thermal desorption spectroscopy revealed that the δ phase exhibits strong hydrogen capture capability, with a hydrogen desorption activation energy of 35.45 ± 2.51 kJ/mol. In addition, spatially resolved hydrogen mapping conducted by scanning Kelvin probe force microscopy and hydrogen microprint technique provided further evidence for the δ phase as a deep hydrogen trapping site. The atomic-scale characterization sufficiently reveals the deformation mechanism of the δ phase induced by dislocation accumulation. Hydrogen-promoted dislocation slip localization facilitates the formation of microvoid defects in the δ phase, which is the main reason for the δ phase fracture, and induces intergranular and transgranular cracks.

Chloride-Induced Stress Corrosion Cracking of Friction Stir-Welded 304L Stainless Steel: Effect of Microstructure and Temperature

Dry storage canisters of used nuclear fuels are fabricated using SUS 304L stainless steel. Chloride-induced stress corrosion cracking (CISCC) is one of the major failure modes of dry storage canisters. The cracked canisters can be repaired by friction stir welding (FSW), a low-heat input ‘solid-phase’ welding process. It is important to evaluate the ClSCC resistance of the friction stir welded material. Stress corrosion cracking (SCC) studies were carried out on mill-annealed base materials and friction stir welded 304L stainless U-bend specimens in 3.5% NaCl + 5 N H2SO4 solution at room temperature and boiling MgCl2 solution at 155 °C. The engineering stress on the outer fiber of the FSW U-bend specimen was ~60% higher than that of the base metal (BM). In spite of the higher stress level of the FSW, both materials (FSW and BM) showed almost similar SCC failure times in the two different test solutions. The SCC occurred in the thermo-mechanically affected zone (TMAZ) of the FSW specimens in the 3.5% NaCl + 5 N H2SO4 solution at room temperature, while the stirred zone (SZ) was relatively crack-free. The failure occurred at the stirred zone when tested in the boiling MgCl2 solution. Hydrogen reduction was the cathodic reaction in the boiling MgCl2 solution, which promoted hydrogen-assisted cracking of the heavily deformed stirred zone. The emergence of the slip step followed by passive film rupture and dissolution of the slip step could be the SCC events in the 3.5% NaCl + 5 N H2SO4 solution at room temperature. However, the slip step height was not sufficient to cause passivity breakdown in the fine-grained SZ. Therefore, the SCC occurred in the partially recrystallized softer TMAZ. Overall, the friction-stirred 304L showed higher tolerance to ClSCC than the 304L base metal.

Influence of Nb on the hydrogen-assisted cracking behaviour in multiphase stainless steel: Phase fractions, stacking fault energies, and nanosized NbC precipitation

Nb alloying has been reported to deteriorate the hydrogen embrittlement resistance of multiphase steels, which contrasts to the case of single-phase metallic materials. This study clarifies the impact of Nb alloying on the hydrogen embrittlement behaviour of a novel multiphase stainless steel. The findings revealed a 17 % reduction in the hydrogen embrittlement sensitivity upon Nb incorporation. It was found that higher austenite fractions in the Nb-bearing steels impeded hydrogen ingress. The austenite phase in such Nb-bearing steels possesses a higher stacking fault energy, thereby delaying martensitic transformation and crack initiation. The precipitation of nanometre-sized NbC in the matrix obstructed hydrogen diffusion, which indirectly inhibited crack initiation and propagation.

On the suitability of single-edge notch tension (SENT) testing for assessing hydrogen-assisted cracking susceptibility

Combined experiments and computational modelling are used to increase understanding of the suitability of the Single-Edge Notch Tension (SENT) test for assessing hydrogen embrittlement susceptibility. The SENT tests were designed to provide the mode I threshold stress intensity factor (Kth) for hydrogen-assisted cracking of a C110 steel in two corrosive environments. These were accompanied by hydrogen permeation experiments to relate the environments to the absorbed hydrogen concentrations. A coupled phase-field-based deformation–diffusion-fracture model is then employed to simulate the SENT tests, predicting Kth in good agreement with the experimental results and providing insights into the hydrogen absorption–diffusion–cracking interactions. The suitability of SENT testing and its optimal characteristics (e.g., test duration) are discussed in terms of the various simultaneous active time-dependent phenomena, triaxiality dependencies, and regimes of hydrogen embrittlement susceptibility.

CO2 effect on the fatigue crack growth of X80 pipeline steel in hydrogen-enriched natural gas: Experiment vs DFT

Utilizing the existing natural gas grid presents a promising method for transporting hydrogen on a large scale. However, the effects of natural gas and its impurities on hydrogen-assisted cracking in pipeline steel have not been adequately studied. This study aims to investigate the fatigue performance of X80 pipeline steel in hydrogen-enriched natural gas (HENG) environments and in mixtures containing the impurity CO2. This is achieved through fatigue crack growth rate (FCGR) tests and density functional theory (DFT) calculations. The experimental results show that the FCGR in H2 is slightly faster than that in HENG, whereas it is slower than that in the N2/CO2/H2 mixtures. The enhanced FCGR by CO2 further increases with the increasing CO2 content. DFT computational results indicate that the adsorbed CO2 on the iron surface significantly accelerates the migration of H atoms from surface to subsurface. This promotes the entry of hydrogen into the steel.

The effect of low hydrogen content on hydrogen embrittlement of additively manufactured 17–4 stainless steel

This work aims to evaluate the impact of small amounts of hydrogen on the hydrogen-assisted cracking (HAC) of 17-4 martensitic stainless steel (SS) prepared by additive manufacturing (AM). To elucidate the effect of processing on the hydrogen–material interactions, the obtained results were compared with a conventionally manufactured (CM) counterpart. It was found that the hydrogen uptake of AM 17-4 SS is higher compared to CM; however, its resistance to HAC is improved. These differences are attributed to the presence of stronger hydrogen trapping sites, retained austenite and the absence of Nb-rich precipitates in the AM 17-4 SS. The effect of processing on the microstructure and the susceptibility to hydrogen-induced damage and hydrogen embrittlement is discussed in detail.

Hydrogen contribution to low temperature embrittlement during PWR exposure of an alloy 82 weld metal

The embrittlement of alloy 82 welds exposed to a simulated pressurised water reactor (PWR) environment was analysed and compared with that observed for cathodically hydrogen-precharged specimens. Similarities in mechanical behaviour, i.e. the evolution of the constitutive equations with a decrease in flow stress compared with non-precharged specimens, and in the fracture modes, with brittle zones in the outer layer, enabled us to conclude that the embrittlement observed in simulated PWR environment corresponded to a two-step hydrogen-assisted cracking mechanism. The first step corresponded to hydrogen absorption into the surface layer leading to crack initiation, and the second step to hydrogen localisation ahead of the crack tip promoting crack propagation.

Hydrogen-assisted cracking and damage tolerance of high-strength lath-martensite steel bars for structural applications

The paper addresses the hydrogen-assisted cracking and damage tolerance of high-strength lath martensite steel bars assessed from slow strain rate tensile tests. These were carried out on fatigue precracked specimens simultaneously charged with hydrogen in a standardized 20 % aqueous solution of ammonium thiocyanate at 50 °C and in air, at room temperature, for comparison. The fractographic analysis of the tested specimens showed the steel sensitivity to hydrogen uptake, which gives rise to the sub-critical extension of the pre-existing crack in two phases, initiation and growth, with both hydrogen-enhanced decohesion (HEDE) and hydrogen-enhanced localized plasticity (HELP) being synergically involved as damage mechanisms. Despite this, the damage tolerance behavior of the steel is highly satisfactory because the crack size causing the steel failure in tension slightly exceeds the theoretical limit of plastic collapse under combined tension and bending loading, regardless of the environment aggressiveness. Although H-assisted failure loads fit the theoretical limit loads, the fast propagation of the crack under constant load beyond the small-scale yielding regime could represent a real threat for the structural use of these steel bars in aggressive media unless the service loads are limited in accordance with such behavior.

Towards a better understanding of hydrogen-assisted cracking in multiphase stainless steel

Given the high strength of multiphase stainless steel, it is imperative to study its hydrogen embrittlement behavior. However, the understanding of hydrogen-assisted crack initiation and propagation is limited. In this study, we investigate the hydrogen-assisted cracking behavior of multiphase stainless steel through crack analysis, hydrogen permeation test, and hydrogen desorption experiments. Our findings reveal that hydrogen-assisted cracks initiate at the martensite packet boundaries and propagate along the packet boundaries, block boundaries, prior austenite grain boundaries and through ferrite. Additionally, we have elucidated the hydrogen trap sources and proposed a hydrogen-assisted cracking mechanism.

Deciphering Hydrogen Embrittlement Mechanisms in Ti6Al4V Alloy: Role of Solute Hydrogen and Hydride Phase.

Ti6Al4V (Ti64) is a versatile material, finding applications in a wide range of industries due to its unique properties. However, hydrogen embrittlement (HE) poses a challenge in hydrogen-rich environments, leading to a notable reduction in strength and ductility. This study investigates the complex interplay of solute hydrogen (SH) and hydride phase (HP) formation in Ti64 by employing two different current densities during the charging process. Nanoindentation measurements reveal distinct micro-mechanical behavior in base metal, SH, and HP, providing crucial insights into HE mechanisms affecting macro-mechanical behavior. The fractography and microstructural analysis elucidate the role of SH and HP in hydrogen-assisted cracking behaviors. The presence of SH heightens intergranular cracking tendencies. In contrast, the increased volume of HP provides sites for crack initiation and propagation, resulting in a two-layer brittle fracture pattern. The current study contributes to a comprehensive understanding of HE in Ti6Al4V, essential for developing hydrogen-resistant materials.

An approach to coupling the gas flow dynamics and thermodynamics of hydrogen solubility in L485ME steel grade for estimation of fracture toughness

The paper presents the problem of coupling the gas flow dynamics in pipelines with the thermodynamics of hydrogen solubility in steel for the estimation of the fracture toughness. In particular, the influence of hydrogen blended natural gas transmission on hydrogen solubility and, consequently, on fracture toughness is investigated with a focus on the L485ME low-alloy steel grade. Hydraulic simulations are conducted to obtain the pressure and temperature conditions in the pipeline. The hydrogen content is calculated from Sievert’s law and, as a consequence, the fracture toughness of the base metal and heat-affected zone is estimated. Experimental data is used to define hydrogen-assisted crack size propagation in steel as well as to a plane strain fracture toughness. The simulations are conducted for a real natural gas transmission system and compared against the threshold stress intensity factor. The results showed that the computed fracture toughness for the heat-affected zone significantly decreases for all natural gas and hydrogen blends. The applied methodology allows for identification of the hydrogen-induced embrittlement susceptibility of pipelines constructed from thermomechanically rolled tubes worldwide most commonly used for gas transmission networks in the last few decades.

Grain Refinement Effect on Resistance to Hydrogen-assisted Crack Growth in Equiatomic CoCrFeNi High-entropy Alloy with Different H Charging Conditions

Grain Refinement Effect on Resistance to Hydrogen-assisted Crack Growth in Equiatomic CoCrFeNi High-entropy Alloy with Different H Charging Conditions

A Phase-Field Regularized Cohesion Model for Hydrogen-Assisted Cracking

Hydrogen-assisted cracking (HAC) usually causes premature mechanical failure of the material and results in structural damage in hydrogen environments. A phase-field regularized cohesion model (PF-CZM) was proposed to address hydrogen-assisted cracking. It incorporated the hydrogen-enhanced decohesion mechanism to decrease the critical energy release rate to address damage initiation and progression in a chemo-mechanical coupled environment. This model is based on coupled mechanical and hydrogen diffusion responses, driven by chemical potential gradients, and the introduction of hydrogen-related fracture energy degradation laws. The coupling problem is solved by an implicit time integral, in which hydrogen concentration, displacement and phase-field order parameters are the main variables. Three commonly used loading regimes (tension, shear, and three-point bending) were provided for comparing crack growth. Specifically, (i) hydrogen-dependent fracture energy degradation, (ii) mechanical–chemical coupling, and (iii) the diffusion coefficient D is influenced by both the phase field and the chemical field. By considering these factors, the PF-CZM model provided a variational framework by coupling mechanical loading with concentration diffusion for studying the complex interplay between a chemo-mechanical coupled environment and material damage, thereby enhancing our understanding of hydrogen-assisted cracking phenomena.

Investigations on hydrogen-assisted cold cracking of laser welded AHSS

AbstractThis study aims to investigate the impact of various surface conditions prior to welding on the susceptibility of materials to cold cracking, including an analysis of fracture surfaces. Additionally, a novel method is introduced for quantifying the presence of diffusible hydrogen using thermal desorption analysis (TDA). This method allows for the determination of diffusible hydrogen concentration in thin sheet welded joints without use of welding consumables. Three different cold-rolled Advanced high-strength steel (AHSS) samples with different surface conditions, such as coatings, lubrication, or water, are examined to assess their susceptibility to cold cracking. In addition to measuring the diffusible hydrogen content in both the base material and the coating, the overall hydrogen content of the base material is also measured using the melt extraction (ME) method. The new method for quantifying diffusible hydrogen in weld metal is applied to investigate different welding variations, intentionally introducing hydrogen through coatings and hydrogenous fluids on the sheet surface. By combining the assessment of cracking susceptibility and hydrogen content, a better understanding of critical hydrogen levels leading to hydrogen-assisted cracking (HAC) is achieved. The results of this study demonstrate that the occurrence of cold cracking in specific AHSS samples increases when either lubrication or both coating and water or lubricant are added. Additionally, the presence of diffusible hydrogen in the welds of all materials is found to increase with the introduction of hydrogenous layers to the material. Although a critical hydrogen content is identified, no clear correlation between the amount of hydrogen and cracking susceptibility can be determined. These findings have significant implications for the welding of cold-formed AHSS, particularly in the automotive industry where safety and lightweight design are of paramount importance.