Eliminating reversible hydrogen embrittlement in high-strength martensitic steel by an electric current pulse

Hydrogen embrittlement has been a great issue in ultrahigh-strength automotive steel applications. Few studies on solving hydrogen embrittlement have been conducted in terms of removing hydrogen, and most studies focus on improving the resistance to hydrogen embrittlement through microalloying. In this study, an electric pulse was used to solve hydrogen embrittlement by removing hydrogen at 120 Hz (frequency), 180 μs (duration), and 200 A (current intensity). The temperature of the samples reached 105 °C under these parameters. Compared with the samples heat treated at the same temperature, the precharged samples processed by electric pulses had a lower hydrogen content and less ductility loss. Moreover, electric pulse processing can also reduce the approximate equilibrium concentration of hydrogen compared with heat treatment. This is due to the introduction of electrical free energy, which reduces the barrier to hydrogen diffusion, and pulsed electric current also accelerates the hydrogen diffusion.     

Suppression of hydrogen embrittlement of gear steel 20CrMnTiH with pulsed electric current

When steel is smelted and used, hydrogen penetration will lead to hydrogen embrittlement, reduce the service life of materials, and even cause safety accidents. Various defects in steel can trap hydrogen atoms as hydrogen traps, resulting in high hydrogen content in materials. In this study, 20CrMnTiH gear steel billets with high hydrogen content were treated by electric pulse. It was found that the elongation and tensile strength of the samples treated by electric pulse were improved, which is attributed to the reduction of diffusible hydrogen content in the sample. Meanwhile, as an irreversible hydrogen trap, FeO's reduction makes it easier for hydrogen atoms to diffuse and escape under the electric field. Pulse current not only promotes the diffusion of hydrogen atoms, but also eliminates some hydrogen traps. The hydrogen control method under pulse current provides another alternative for solid state dehydrogenation and repair of hydrogen embrittlement fracture.     

On the role of hydrogen in the stress corrosion cracking behavior of Q345R steel in HF vapor environment

The stress corrosion cracking (SCC) behavior of Q345R steel in hydrofluoric acid (HF) vapor environment was investigated. It is shown that Q345R has a high susceptibility to SCC in HF vapor environment, which is negatively correlated with the strain rate. Several different crack morphologies and cracking factors are verified: flat cracks in ferrite are associated with anodic dissolution triggered by micro-galvanic corrosion, and porous cracks at the pearlite and pearlite-ferrite interfaces are mainly influenced by hydrogen. The results of hydrogen charging tests show that pre-charging has little effect on the hydrogen embrittlement of Q345R steel, while in-situ charging leads to severe brittle fracture of the material, because hydrogen interacts with large number of moving dislocations generated by in-situ stretching process and penetrates more readily into the material. The synergistic relationship between hydrogen and dislocation motion is found to be the main mechanism for the transition from ductile to brittle fracture.     

Analysis of electrochemical hydrogen permeation through X-65 pipeline steel and its implications on pipeline stress corrosion cracking

Electrochemical hydrogen permeation tests were performed to measure the hydrogen permeation current through the X-65 pipeline steel in the electrolytes simulating the soil conditions to initiate near-neutral pH stress corrosion cracking (SCC) in pipelines. The hydrogen permeation current was analyzed following the constant concentration model. It is shown that, AQDS, simulating the organic compound in the soil, inhibits hydrogen permeation by decreasing the sub-surface hydrogen concentration, while sulfide promotes hydrogen permeation by inhibiting the hydrogen recombination and thus increasing the sub-surface hydrogen concentration. The steel specimen is more susceptible to stress corrosion cracking in the soil solution with a higher sub-surface hydrogen concentration, indicating that hydrogen is involved in near-neutral pH SCC in pipelines. It is suggested that hydrogen promotes the cracking of the steel, accompanying with the anodic dissolution on the crack sides and at the crack tip.     

Effects of vanadium precipitates on hydrogen trapping efficiency and hydrogen induced cracking resistance in X80 pipeline steel

In this study, the number and size distribution of vanadium precipitates and their effects on hydrogen trapping efficiency and hydrogen-induced cracking (HIC) susceptibility were investigated in X80 pipeline steel. The results showed that as the vanadium content increased, the number of nanoscale vanadium precipitates clearly increased. Furthermore, the amount of hydrogen atoms trapped by vanadium precipitates gradually increased and the hydrogen diffusion coefficient decreased from 4.74 × 10^?6 cm² s^?1 in the vanadium-free V0 steel to 8.48 × 10^?7 cm² s^?1 in the V4 steel with 0.16% V, according to hydrogen permeation results. It also reduced the possibility of hydrogen atoms diffusing into the sites of harmful defects such as large-size oxides and elongated MnS inclusions, where cracks were caused more easily. In addition, the V3 steel with 0.12% V, containing the largest number of vanadium carbide particles of less than 60 nm, had the lowest HIC susceptibility.     

Continuous monitoring of back wall stress corrosion cracking growth in sensitized type 304 stainless steel weldment by means of potential drop techniques

Stress corrosion cracking (SCC) tests on welded specimens of sensitized type 304SS with a thickness of 20 mm were performed in sodium thiosulphate solution at room temperature, with continuous monitoring of the SCC growth, using the techniques of modified induced current potential drop (MICPD), alternating current potential drop (ACPD) and direct current potential drop (DCPD). The MICPD and DCPD techniques permit continuous monitoring of the back wall SCC, which initiates from a fatigue pre-crack at a depth of about 4 mm, from which it propagates through more than 80% of the specimen thickness. The MICPD technique can decrease the effect of the current flowing in the direction of the crack length by focusing the induced current into the local area of measurement using induction coils, so that the sensitivity of the continuous monitoring of the back wall SCC is higher than that of the ACPD and DCPD techniques.     

Effect of Ce content on the hydrogen induced cracking of X80 pipeline steel

In this study, the effect of Ce content on hydrogen induced cracking (HIC) of X80 pipeline steel has been investigated. The results show that as the Ce content increased from 0 wt% to 0.0042 wt%, 0.016 wt% and 0.024 wt%, the HIC susceptibility of tested steels decreased first and then increased. The steel containing 0.016 wt% Ce possessed the lowest HIC susceptibility because Ce modified inclusions, promoted the formation of acicular ferrite, and decreased the number of hydrogen traps and intergranular cracks.     

Investigation of the hydrogen induced cracking behaviour of API 5L X65 pipeline steel

The effect of microstructural features on the hydrogen induced cracking (HIC) susceptibility of two API 5L X65 pipeline steels were investigated by cathodic charging, hydrogen permeation and hydrogen microprint experiments. Microstructural evaluation after hydrogen charging revealed cracks at the mid-thickness (segregation zone) of both plates. However, more severe cracks were observed in the plate with higher dislocation density and residual stresses. The plate with lower plastic strain and more {111}-oriented grains had less severe cracks. Inclusions found along the crack path, comprising of Si-enriched oxides and carbides contributed to the initiation and propagation of cracks. The variation of the trapping behaviour and hydrogen diffusion through the plates were examined. The results confirmed that a higher ratio of reversible to irreversible traps contributes to increasing HIC severity in steels. Additionally, hydrogen transport through the steels was most prominent along the grain boundaries, indicating the importance of grain boundary character to HIC.     

Safety assessment of austenitic steel nuclear power plant pipelines against stress corrosion cracking in the presence of hybrid uncertainties

Stress corrosion cracking (SCC) is an important degradation mechanism to be considered for safety assessment of nuclear piping components made of austenitic steels, especially in the heat-affected zones. Damage due to SCC occurs in a susceptible material, in a corrosive environment, in the presence of high temperature and high applied/residual stresses. The operating conditions and the environmental conditions show variations during the lifetime of the power plant. Also, there will be variations in micro-structural properties of the material of piping components. These variations should be taken into account while assessing the safety of the piping component against SCC. This can be accomplished by treating the relevant variables as random or fuzzy depending upon the source and type of uncertainty. In this paper, an attempt has been made to compute the fuzzy failure probabilities of a piping component against SCC with time, using an approach combining the vertex method with the Monte Carlo simulation technique. The initiation and propagation stages of stress corrosion cracks are modelled using a modified PRAISE approach. The degree of sensitisation, material fracture toughness, yield strength, ultimate strength and applied stress are considered as random variables, while operating temperature and oxygen concentration are considered as fuzzy variables. The R6 procedure is used in the computation of the fuzzy failure probabilities. The usefulness of the approach is demonstrated through an example problem.     

The effect of hydrogen content and welding conditions on the hydrogen induced cracking of the API X70 steel weld

The self-restraint testing was used to investigate the influence of hydrogen content, preheating, and post-heating on the sensitivity of welding of API X70 pipeline steel to hydrogen induced cracking (HIC). The variation of hydrogen content was applied using a low hydrogen electrode E8018-G and a high hydrogen (cellulosic) electrode E8010-P1. Diffusible hydrogen of these electrodes was measured by mercury displacement method. The average diffusible hydrogen content of cellulosic electrode E8010-P1 and low hydrogen electrode E8018-G were 43.6 and 1.1 ml/100 g of weld metal, respectively. The results of visual inspection, penetrant test, and macroscopic examination showed that welding with cellulosic electrode leads to cracking unless both preheating and post-heating are applied. However, in the case of low hydrogen electrode, cracking occurs only if no preheating or post-heating is applied. The microstructure of the welded specimens in different conditions by optical and scanning electron microscopy (SEM) showed that the dominant phase in the weld zone of all specimens is bainite. The microhardness profile displayed that hardness limitation (350 HV) cannot predict the sensitivity to cold cracking; therefore, other parameters such as hydrogen content should also be considered.     

Stress corrosion cracking behavior of ZK60 magnesium alloy under different conditions

The stress corrosion cracking (SCC) behavior of ZK60 magnesium alloy was investigated under different conditions, i.e. thin electrolyte layer (TEL) and solution, by slow strain rate tensile tests, electrochemical techniques, Auger electron spectroscopy, scanning electron microscopy coupled with electron backscattered diffraction, and time of flight secondary ion mass spectrometry. Results indicated that the ZK60 magnesium alloy in solution exhibits a higher SCC susceptibility with a combined SCC mechanism of weaker anodic dissolution (AD) and stronger hydrogen embrittlement (HE) compared to under TEL. Moreover, the HE mechanism under various conditions was discussed.     

Combined impact of elastic stress,prestrain and electrochemical charging on the hydrogen-induced cracking of high-strength steel

The elastic stress, prestrain and electrochemical hydrogen charging were controlled separately using a stress ring to investigate their roles in the initiation of hydrogen-induced cracks. The brittle features of hydrogen charging-induced damages, i.e., a mixture of quasi-cleavage and intergranular cracks, on the fracture surface were confirmed for a high-strength steel, made possible by applying degassing and tension-to-fracture to the hydrogen-charged specimens. The hydrogen charging-induced cracks eliminated the ductility of material, leading to premature fracture before the yield point in subsequent tensile tests. The strong dependence of hydrogen-induced cracking sensitivity on hydrogen concentration and hydrogen charging time was observed. X-ray microtomography and tensile tests were also utilized to investigate the effect of inclusions on crack formation. This study contributes to the understanding of the combined effects of residual stress and hydrogen on the cracking of deformed steel plates.     

Comprehensive study on hydrogen induced cracking of electrical resistance welded API X52 pipeline steel

Different heat treatment cycles were designed in order to investigate the effect of microstructural changes on hydrogen induced cracking resistance (HIC) and mechanical properties of the electric resistance welded steel. The heat treating of the as-welded specimen improved the ductility and impact toughness. After heat treatment, the uniform hardness profile was obtained for the welded specimens. The removal of local hard zones reduced the risk of HIC. The chemical composition and clustering of inclusions have a deleterious effect on cracking resistance in the H₂S environment. Aluminosilicate compounds and MnS inclusions were favorite sites for HIC. The most promising post weld heat treatment for improving mechanical properties and the resistance to HIC was the application of two-cycle quenching followed by tempering.     

Hydrogen trapping and hydrogen induced cracking of welded X100 pipeline steel in H2S environments

Hydrogen induced cracking (HIC) susceptibility of the welded X100 pipeline steel was evaluated in NACE “A” solution at room temperature according to the NACE TM0284-2011 standard. Both the kinetic parameters of the permeability $\left(J_{\infty }L\right)$, the apparent diffusivity (D_app) and the concentration of reversible and irreversible hydrogen in the base metal and welded joint of X100 pipeline steel were quantitatively investigated by hydrogen permeation test. The results showed that the welded joint with an inhomogeneous microstructure had a higher trap density and more susceptible to HIC due to two orders of magnitude larger in the concentration of irreversible hydrogen than that of base metal, though all presenting poor HIC resistance for both base metal and the welded joint. The HIC cracks initiated from the inclusions enriching in Al, Ca, Si, Mn. The cracks are primarily transgranular, accompanying with limited intergranular ones.     

Evolution of microstructure and texture in pipeline steels at different TMCP procedures with regard to hydrogen induced cracking

SEM and EBSD techniques are used to evaluate hydrogen induced cracking susceptibility in API X70 pipeline steels produced by thermo-mechanical controlled process (TMCP) in laboratory scale. Based on the observations, there is no dominant texture in the specimens and the grains are randomly distributed. Different TMCP parameters and rolling processes generates different grain size, and grains are often elongated along the rolling direction. The results also show that cooling rate is another factor affecting the grain size. A high cooling rate does not allow the grains to grow. The reason for the transgranular type of cracking might be the strong grain boundaries in ambient temperatures which prevents the intergranular cracking. Based on experiments, the hydrogen environment does not have permanent effects on the mechanical properties of the investigated specimens. The electrochemical hydrogen charging experiment shows that the grain refinement improves the resistance to hydrogen embrittlement.     

The effects of double notches on the mechanical properties of a high-strength pipeline steel under hydrogen atmosphere

Tensile tests and fatigue life tests are performed on double-notched specimens in hydrogen and nitrogen atmospheres to investigate the effects of double notches on the mechanical properties of a high strength pipeline steel. The results show that the fracture occurs at the notch with a lower stress concentration factor (Kt), which is governed by the combination of the stress concentration and the strain hardening caused by plastic deformation in the tensile process. Hydrogen gas accelerates the crack initiation and growth, but it doesn't affect the competitive mechanism of stress concentration and strain hardening.     

Hydrogen generation during the corrosion of carbon steel in crotonic acid and using some organic surfactants to control hydrogen evolution

The purpose of this paper is to describe and evaluate the corrosion of carbon steel in crotonic acid for hydrogen production and using polysorbate 20 (NS), dioctyl sodium sulfosuccinate (AS) and benzalkonium chloride (CS) to control hydrogen evolution. Measurements were conducted in tested solutions using hydrogen evolution and electrochemical impedance spectroscopy (EIS) measurements and complemented by scan electron microscope (SEM) and energy dispersive X-ray (EDX) investigations. It is shown that the hydrogen generation rate obtained during the corrosion of carbon steel in crotonic acid increased with increase in acid concentration, temperature and immersion time. The addition of organic surfactants inhibits the hydrogen generation rate. The inhibition occurs through adsorption of organic surfactants on the metal surface. Adsorption processes followed the Langmuir isotherm. The order of effectiveness of the surfactants was AS > NS > CS. The values of activation energy (E_a) and heat of adsorption (Q_ads) were calculated and discussed.     

Insights into the role of partially mixed zones in sulfide stress corrosion cracking of the inconel 625/X80 weld overlay

Sulfide stress corrosion cracking (SSCC) behavior of the fusion boundary (FB) region of Inconel 625/X80 weld overlay was investigated with a focus on the role of the beach and peninsula partially mixed zones (PMZs). Compared to the martensite-ferrite boundary, the large misorientation and low deformation compatibility of the austenite-martensite boundary promote the accumulation of hydrogen and thus increase the cracking susceptibility. Further, under the effect of local anodic dissolution and hydrogen accumulation due to the large dimension PMZ, the corrosion defect formed at the junction can be easily transformed into a crack. After SSCC initiation, the crack preferentially grows along the Inconel 625/PMZ interface while the austenite matrix may oblige the crack to propagate along the FB. In addition, the beach PMZ likely shows a higher SSCC susceptibility than the peninsula PMZ mainly because severe anodic dissolution in the peninsula structure blunts the crack tip along the FB during crack propagation.     

Effects of hydrogen-charging on the susceptibility of X100 pipeline steel to hydrogen-induced cracking

In this work, the hydrogen-induced cracking (HIC) behavior of X100 pipeline steel was investigated by a combination of tensile test, electrochemical hydrogen permeation measurement and surface characterization techniques. The effect of inclusions in the steel on the crack initiation was analyzed. Results demonstrated that the amount of hydrogen-charging into the X100 steel specimen increases with the charging time and charging current density. Hydrogen-charging will enhance the susceptibility of the steel to HIC. The cracks initiate primarily at inclusions, such as aluminum oxides, titanium oxides and ferric carbides, in the steel. The diffusivity of hydrogen at room temperature in X100 steel is determined to be 1.04 × 10⁻⁸ cm²/s.     

Long term integrity against corrosion of titanium used for TRU waste container

Abstract

Commercial grade pure titanium containing palladium (Ti-Grade 17) may be used for transuranic waste containers. The long term integrity of Ti-Grade 17 against corrosion was studied in the concrete permeated alkaline sodium water environment of 0·6 mol [Cl^?]+0·223 mol [OH^?] at various temperatures up to 80°C. The study focused on the stability of the passive oxide film, the susceptibility to crevice corrosion and cracks in the titanium hydride (TiH₂) layer. General corrosion depth for sustained passivation may be determined as i_pass times the evaluation period of 10⁴ years, with addition of the electric quantity for the destruction and repair of passivation film. Crevice corrosion sensitivity is not affected by processes such as welding, cold work and heat treatment. Cathodic reactions essential for maintaining the passive state produce hydrogen that, to some extent, is adsorbed to form a hydride layer. This layer subsequently undergoes cracking to cause reduction in the critical hydride layer thickness δ_c of 10 μm. The crack depth becomes as much as 100 μm at 2000 years.