Effects of tungsten on the hydrogen embrittlement behaviour of microalloyed steels

The effects of tungsten (W) additions (0, 0.1, 0.5 and 1 wt.%) on the hydrogen embrittlement behaviour of microalloyed steels were systematically investigated by means of slow strain rate tests on circumferentially notched cylindrical specimens, and the mechanism of hydrogen-induced embrittlement was discussed. W addition is found to increase the activation energy of hydrogen desorption. Microstructural features affect the hydrogen embrittlement behaviour and fracture modes of microalloyed steels. It is suggested that the hydrogen-induced embrittlement in the studied microalloyed steels with different W additions is caused by the combined effects of decohesion and internal pressure in the presence of hydrogen.     

Corrosion-induced hydrogen embrittlement in aluminum alloy 2024

The present paper focuses on the observed corrosion-induced embrittlement of alloy 2024 and tries to answer the key question on whether the observed embrittlement is attributed to hydrogen uptake and trapping in the material. Hydrogen is produced during the corrosion process and is being trapped in distinct energy states, which correspond to different microstructural sites. The formation of a hydrogen-affected zone beneath the corrosion layer is supported by fractographic analysis. Removal of the corrosion layer leads to complete restoration of yield strength but only partial restoration of ductility. Additional heat treatment to release the trapped hydrogen leads only to complete restoration of ductility.     

Study of the electrochemical permeation of hydrogen in iron

Hydrogen permeation through iron membranes of different thicknesses was studied by the electrochemical permeation technique. The membranes were charged with hydrogen by galvanostatic cathodic polarization in 0.1 M NaOH at 25 °C.The measured build-up and decay permeation current transient had been examined.The experimental results revealed that the diffusion apparently increases with decreasing membrane thickness. This result suggests that the hydrogen transport through membrane was mainly governed by hydrogen trapping at the trap sites present at the grain boundaries.The influence of the passive layer on the hydrogen permeation and its influence on the evaluation of diffusion and trapping characteristics were discussed.     

Double electrolyte sensor for monitoring hydrogen permeation rate in steels

An amperometric hydrogen sensor with double electrolytes composed of a gelatiniform electrolyte and KOH solution has been developed to determine the permeation rate of hydrogen atoms in steel equipment owing to hydrogen corrosion. The gelatiniform electrolyte was made of sodium polyacrylate (PAAS), carboxyl methyl cellulose (CMC) and 0.2 mol dm⁻³ KOH solution. The results show that the gelatiniform electrolyte containing 50 wt.% polymers has suitable viscosity and high electrical conductivity. The consistent permeation curves were detected by the sensor of the double electrolyte and single liquid KOH electrolyte, respectively. The developed sensor has good stability and reproducibility at room temperature.     

The effects of cold rolling and sensitisation on hydrogen embrittlement of AISI 304L welds

The notched tensile strength (NTS) of 304L stainless steel welds subjected to cold rolling (20% thickness reduction) and sensitisation treatment (600 °C/10 h) was measured in a MgCl₂ (40 wt.%) solution at 80 °C. The NTS loss, which is used for comparing the susceptibility to hydrogen embrittlement (HE), was consistent with the extent of embrittled area on the fracture surface of various welds. The HE susceptibility of the weld decreased after cold working but increased with the additional sensitisation treatment of the cold-rolled welds. Besides, cracks tended to propagate along the skeletal boundaries for all welds tested in the MgCl₂ solution.     

Strengthening and hydrogen embrittlement of ultrafine-grained Fe–0.01 mass% C alloy processed by high-pressure torsion

This study was conducted to elucidate the effects of annealing and hydrogenation on the tensile properties of an Fe–0.01 mass% C alloy processed by high-pressure torsion (HPT). By HPT processing, the tensile strength was increased to ∼1500 MPa through grain refinement. Low-temperature annealing further strengthened the HPT-processed specimen because of a simultaneous effect of carbide precipitation and grain refinement. Reduction in the dislocation density and the fraction of low-angle grain boundaries through warm-temperature annealing led to a decrease in hydrogen uptake when the specimens were exposed to high-pressure gaseous hydrogen, and they became less sensitive to hydrogen embrittlement (HE).     

The effects of sacrificial coatings on hydrogen embrittlement and re-embrittlement of ultra high strength steels

This paper describes an investigation of electrodeposited Zn-14% Ni and aluminium-based SermeTel 1140/962 coatings as possible replacements for cadmium. Slow strain rate tests were performed to measure the extent of direct hydrogen embrittlement of a high strength steel substrate as a result of the coating process and of hydrogen re-embrittlement caused by coating corrosion. The level of re-embrittlement was shown to depend on both the electrochemical potential of the coating and its barrier properties. Zn-14% Ni coatings caused the most re-embrittlement as they had the most active potential and contained through-thickness defects which left the steel exposed to hydrogen uptake. The microstructure of the high strength steel was also shown to be an important factor affecting the extent of embrittlement. AerMet 100 steel was more resistant than 300M steel and this was attributed to the presence of reverted austenite surrounding the martensite laths in AerMet 100, which trapped absorbed hydrogen and prevented a critical hydrogen concentration being reached in the more susceptible martensite phase.     

Hydrogen embrittlement of high strength pipeline steels

A comparison was made between three API grade pipeline steels (X60, X80 and the X100 grade) from the point of view of their susceptibility to hydrogen embrittlement. The main aim was to determine whether the development of higher strength materials led to greater susceptibility to hydrogen embrittlement. This was achieved by straining at 2.8 × 10⁻⁵ s⁻¹ after cathodic charging. The results showed that there is a distinct susceptibility to loss of ductility after charging and this tends to increase with the strength level of the steel at a charging current density above 0.44 mA mm⁻². All three steels exhibited fine cracks parallel to the major rolling direction after charging and an increasing amount of brittleness on the fracture surface.     

Internal and surface damage of multiphase steels and pure iron after electrochemical hydrogen charging

High strength steels appear to be even more prone to hydrogen embrittlement (HE). In this work, pure iron and a ferrite–bainite steel were charged electrochemically using various electrolytes and combinations of current density and charging time to identify the experimental conditions where blister formation occurred. The appearance and propagation of cracks inside the sample were studied also by means of high resolution scanning electron microscopy. The study was repeated for a dual phase (DP) steel; a TRIP steel and a high strength low alloy (HSLA), which allowed to get an indication on the effect of variable microstructural characteristics.     

The effect of grain size and aging on hydrogen embrittlement of a maraging steel

Notched tensile tests were conducted under a slow displacement rate to evaluate the influences of grain size and aging on hydrogen embrittlement (HE) of T-200 maraging steel. In addition, an electrochemical permeation method was employed to measure the effective diffusivity (D_eff) and apparent solubility (C_app) for hydrogen of various heat-treated specimens. The results indicated that the aged (482 °C/4 h) specimens comprised of numerous precipitates led to a raised C_app and a decreased hydrogen diffusivity as compared to those of the solution-treated ones. The solution-treated specimens were resistant to gaseous HE, whereas aged specimens were susceptible to it, implying the strength level was the controlling factor to affect the HE susceptibility of the specimens. Nevertheless, all specimens suffered from sulfide stress corrosion cracking (SSCC) severely but to different degrees. The aged specimens were more likely to form intergranular (IG) fractures in H₂S but quasi-cleavage (QC) in H₂. For the solution-treated specimens, a fine-grained structure was susceptible to HE in H₂S and revealed mainly QC that differed from the IG fracture of the coarse-grained one. The fracture mode of the specimens could also be related to the transport path and / or the supply of hydrogen to the plastic zone of notched specimens in hydrogen-containing environments.     

Influence of residual stresses and strains generated by cold drawing on hydrogen embrittlement of prestressing steels

Hydrogen embrittlement plays an important role in environmental cracking of prestressing steel wires. The ammonium thiocyanate test (ATT) was implemented as a standard for determination of their susceptibility to environmentally assisted fracture. However, ATT reveals neither how hydrogen induced fracture (HIF) goes on in steel nor the roles of important manufacturing and service factors. To this end, the knowledge of the residual stresses and plastic strains in wires due to cold drawing, as well as the hydrogenation from harsh environments, are the keys to successful predictions of wire lives. This paper advances previous analyses of HIF in cold drawn prestressing wires via numerical modelling, firstly, of the cold drawing process to obtain the distributions of residual stresses and plastic strains, and secondly, of the stress-strain assisted hydrogen diffusion in wires towards creation the conditions for HIF nucleation. Generated results prove the relevant role of residual stress-and-strain field in hydrogen diffusion in the wires, as well as their possible consequences for HIF.     

Role of microstructure, composition and hardness in resisting hydrogen embrittlement of fastener grade steels

The degree of hydrogen embrittlement for several fastener grade steels has been determined. While microstructural alteration resulted in some improvement in resistance to hydrogen embrittlement, the overriding factor contributing to susceptibility of the steel was strength. The degree of susceptibility of the microstructures to hydrogen embrittlement, ranked in increasing order, is as follows: fine pearlite, bainite, tempered martensite. The effects of alloying were also assessed by comparing results from different fastener grade steels with similar microstructures. In most cases, the alloy chemistry had little effect, presumably due to trap saturation associated with this testing technique.     

Hydrogen transport and embrittlement in 300 M and AerMet100 ultra high strength steels

This paper describes how hydrogen transport affects the severity of hydrogen embrittlement in 300 M and AerMet100 ultra high strength steels. Slow strain rate tests were carried out on specimens coated with electrodeposited cadmium and aluminium-based SermeTel 1140/962. Hydrogen diffusivities were measured using two-cell permeation and galvanostatic charging methods and values of 8.0 × 10⁻⁸ and 1.0 × 10⁻⁹ cm² s⁻¹ were obtained for 300 M and AerMet100, respectively. A two-dimensional diffusion model was used to predict the hydrogen distributions in the SSR specimens at the time of failure. The superior embrittlement resistance of AerMet100 was attributed to reverted austenite forming around martensite laths during tempering.     

Hydrogen embrittlement of stainless steel overlay materials for hydrogenators

An investigation was carried out of the effect of hydrogen absorption on the tensile ductility of composite specimens representing stainless steel weld overlays on low alloy steel substrates as used in the fabrication of hydrogenators. Specimens of the two stainless steels (AISI 309 and 347) involved in hydrogen cracking were also fractured in tension at strain rates between 5.9 × 10⁻⁶ and 1.5 × 10⁻³ s⁻¹ after thermal charging with hydrogen. Results indicated that only the 347 samples suffered significant embrittlement by hydrogen and the original ductility could be restored by subsequent annealing for a time and temperature determined by the hydrogen diffusivity.     

Quantitative evaluation of detection efficiency of the hydrogen microprint technique applied to steel

The detection efficiency of a hydrogen microprint technique (HMT) applied to steel specimens was examined experimentally. Amounts of hydrogen released from the specimen surface were measured by an electrochemical hydrogen permeation method, and the amounts were also evaluated by means of HMT under the same charging conditions as employed for the permeation test. Detection efficiency of conventional HMT was found to be as low as about 1%, but nickel plating of the steel surface was found to increase this efficiency remarkably. This high efficiency by nickel plating was achieved only when the relative humidity of an experimental atmosphere was controlled to 80% or higher. The thus-modified HMT showed a detection efficiency of about 40%.     

Sintered stainless steels: Fatigue crack propagation resistance under hydrogen charging conditions

Monophasic and multiphasic (two and three phases) sintered stainless steels were prepared both considering premixes of AISI 316LHC and AISI 434LHC stainless steels powders and using a prealloyed duplex stainless steel 25% Cr, 5% Ni, 2% Mo powder. Their fatigue crack propagation resistance was investigated both in air and under hydrogen charging conditions (0.5 M H₂SO₄ + 0.01 M KSCN aqueous solution; applied potential = −700 mV/SCE), considering three different stress ratios (R = 0.1; 0.5; 0.75). Fatigue crack propagation micromechanisms were investigated by means of fracture surface scanning electron microscope (SEM) analysis.For all the investigated sintered stainless, fatigue crack propagation resistance is influenced by hydrogen charging and an increase of crack growth rates dependent on the steel microstructure is obtained. Experimental results also allow to identify the sintered stainless steel obtained from the prealloyed 25% Cr, 5% Ni, 2% Mo powder as the most resistant to fatigue crack propagation in air and under hydrogen charging conditions.     

Comparative assessment of electrochemical hydrogen absorption by pipeline steels with different strength

The assessment of ability to absorb hydrogen of three API grade pipeline steels: X52, X70 and X100 have been evaluated. The factors of cathodic hydrogen charging, time of exposure, and applied stress were taken into account. It has been shown that all steels demonstrate the sensitivity to hydrogenating in deoxygenated, near-neutral pH NS4 solution under relatively “soft” cathodic polarisation, although the efficiency of hydrogen permeation in metal is quite low and depends on time of exposure. Applied tensile stress, which equivalent to gross hoop stress in pipe wall under operating conditions, can accelerate the hydrogen absorption in several times. For studied steels the resistance to hydrogen absorption decreases with decreasing of steel strength.     

Effect of post-weld heat treatment on the microstructure and hydrogen permeation of 13CrNiMo steels

The hydrogen trapping characteristics of 13CrNiMo martensitic steel weld metals, with different austenite contents resulting from different post-weld heat treatments, have been analysed. Scanning electron microscopy and X-ray diffraction have been used to study stable austenite resulting from intercritical tempering of these soft martensitic stainless steels weld metals. Austenite contents up to 25 vol.% have been obtained. Hydrogen diffusion and permeation coefficients have been obtained from an analysis of the permeation rate of hydrogen through these materials. A decrease of the hydrogen apparent diffusion coefficient is observed when the tempering temperature is increased in the range ; this decrease is attributed to changes in the martensitic matrix as well as to the increase of austenite content. The role of the austenite phase on trapping is discussed.