Hydrogen Embrittlement of Nitrogenating Layer on Martensitic Alloys

Nitriding of the surface in martensitic stainless steels is commonly carried out to improve their wear resistance. The process of plasma nitriding in stainless steel is influenced by two mechanisms: physical diffusion through the surface and chemical gas-metal reaction. The inner nitriding interaction involves the simultaneous penetration and formation of a solid solution, as well as the interaction of nitrogen with specific alloying elements, resulting in the development of homogeneous and heterogeneous structures. Our study concludes that the observed intergranular hydrogen embrittlement and crack formation during the surface nitridation process of AMS 5719 martensite alloy steel can be attributed to the ammonium concentration of approximately 50% at a temperature of 530˚C.

Hydrogen embrittlement of X80 pipeline steel in H2S environment: Effect of hydrogen charging time, hydrogen-trapped state and hydrogen charging–releasing–recharging cycles

This study investigated the susceptibility of X80 pipeline steel to hydrogen embrittlement given different hydrogen pre-charging times and hydrogen charging–releasing–recharging cycles in H2S environment.The fracture strain of the steel samples decreased with increasing hydrogen pre-charging time;this steel degradation could almost be recovered after diffusible hydrogen was removed when the hydrogen pre-charging time was<8 d.However,unrecoverable degeneration occurred when the hydrogen pre-charging time extended to 16–30 d.Moreover,nanovoid formation meant that the hydrogen damage to the steel under intermittent hydrogen pre-charging–releasing–recharging conditions was more serious than that under continuous hydrogen pre-charging conditions.This study illustrated that the mechanical degradation of steel is inevitable in an H2S environment even if diffusible hydrogen is removed or visible hydrogen-induced cracking is neglected.Furthermore,the steel samples showed premature fractures and exhibited a hydrogen fatigue effect because the repeated entry and release of diffusible hydrogen promoted the formation of vacancies that aggregated into nanovoids.Our results provide valuable information on the mechanical degradation of steel in an H2S environment,regarding the change rules of steel mechanical properties under different hydrogen pre-charging times and hydrogen charging–releasing–recharging cycles.

ELECTRONIC STATES AND HYDROGEN EMBRITTLEMENTIN TRANSITION METALS

An electronic approach to the mechanism of hydrogen embrittlement in metals is pre-sented and discussed. Some problems of the mechanism of hydrogen embrittlement are pointed out from an electronic point of view. Electronic structure calculations in a periodically cleaved or slipped lattice are developed in orker to identofy deformation-sensitive electronic states in the absence of hydrogen. The calculational results are given and discussed for a trunsition metal, Pd. Electronic structure calculations in the presence of hydrogen are outlined and hydrogen embrittlement in transition metals is discussed in terms of electronic states.

Effect of in-situ nanoparticles on the mechanical properties and hydrogen embrittlement of high-strength steel

We investigated the critical influence of in-situ nanoparticles on the mechanical properties and hydrogen embrittlement(HE)of high-strength steel.The results reveal that the mechanical strength and elongation of quenched and tempered steel(919 MPa yield strength,17.11%elongation)are greater than those of hot-rolled steel(690 MPa yield strength,16.81%elongation)due to the strengthening effect of insitu Ti_(3)O_(5)–Nb(C,N)nanoparticles.In addition,the HE susceptibility is substantially mitigated to 55.52%,approximately 30%lower than that of steels without in-situ nanoparticles(84.04%),which we attribute to the heterogeneous nucleation of the Ti_(3)O_5 nanoparticles increasing the density of the carbides.Compared with hard TiN inclusions,the spherical and soft Al_(2)O_(3)–MnS core–shell inclusions that nucleate on in-situ Al_(2)O_(3) particles could also suppress HE.In-situ nanoparticles generated by the regional trace-element supply have strong potential for the development of high-strength and hydrogen-resistant steels.

Effect of shot peening on hydrogen embrittlement of high strength steel

The effect of shot peening（SP） on hydrogen embrittlement of high strength steel was investigated by electrochemical hydrogen charging, slow strain rate tensile tests, and hydrogen permeation tests. Microstructure observation, microhardness, and X-ray diffraction residual stress studies were also conducted on the steel. The results show that the shot peening specimens exhibit a higher resistance to hydrogen embrittlement in comparison with the no shot peening（NSP） specimens under the same hydrogen-charging current density. In addition, SP treatment sharply decreases the apparent hydrogen diffusivity and increases the subsurface hydrogen concentration. These findings are attributed to the changes in microstructure and compressive residual stress in the surface layer by SP. Scanning electron microscope fractographs reveal that the fracture surface of the NSP specimen exhibits the intergranular and quasi-cleavage mixed fracture modes, whereas the SP specimen shows only the quasi-cleavage fractures under the same hydrogen charging conditions, implying that the SP treatment delays the onset of intergranular fracture.

Hydrogen Embrittlement Processes and Al/Al_2O_3 Hydrogen Resistance Coatings of NdFeB Magnets

After analyzing the phenomena and processes of hydrogen embrittlement of NdFeB permanent magnets, RF magnetron sputtering was used to fabricate Al thin films and then oxidized to form the Al/Al_2O_3 composite films on the magnets as the hydrogen resistance coatings. SEM and EDS were used to examine the morphology and composition respectively. Hydrogen resistance performance was tested by exposing the magnets in 10 MPa hydrogen gas at room temperature. The results show that the magnets with 8 μm Al/Al_2O_3 coatings can withstand hydrogen of 10 MPa for 65 min without being embrittled into powder. The samples with and without hydrogen resistance coatings have almost the same magnetic properties.

EFFECT OF AGING ON HYDROGEN EMBRITTLEMENT SUSCEPTIBILITY OF STEEL Cr21Ni6Mn9N

Effects of 650℃ aging for 1—1000 h on structure and hydrogen embrittlement susceptibility (HES)of steel Cr21Ni6Mn9N have been investigated.The results show that M_(23)C_6 type carbide precipitates at grain boundaries and Cr-depletive region appears beside them during aging.The precipitates grow and connect each other as the aging time prolongs.Meanwhile, the degree of Cr-depletion aggravates first and then recovers gradually while the aging time is very long,i.e.,1000 h.The HES of the steel increases with increasing aging time but does not reduce with the recovery of Cr content at the Cr-depletive region.That implies that the ex- isting of carbides at grain boundaries might be the main reason which promotes the HES of steel during aging.

EFFECT OF COMPOSITION ON HYDROGEN EMBRITTLEMENT IN Ni-Fe FCC ALLOYS

The ductility loss and threshold stress intensity,K_(IH)during hydrogen charging were measured for pure Ni and four Ni-Fe fcc alloys.The results show that ductility loss in 40Ni60Fe alloy and K_(IH)a 50Ni50Fe alloy have a minimum value.The variations of the amounts of hydride, hydrogen evolution and dislocation structure with composition have been investigated.The va- riation of hydrogen embrittlement susceptibility with composition measured by ductility loss and by K_(IH)or K_(IH)/K_C can be explained by means of the synthetical effects of amount of hydride,solutionized hydrogen and the extent of dislocation planarity on hydrogen embrittlement susceptibility.

Effect of vanadium on hydrogen embrittlement of grade 12.9 high-strength bolt steels

In this study, the effect of vanadium addition(0.25%) on microstructure and hydrogen embrittlement(HE) was investigated in grade 12.9 bolt steels, and hydrogen diffusion was analyzed by hydrogen permeation.The results show that the addition of 0.25% vanadium in bolt steels can significantly improve the HE resistance.Vanadium addition can form a large number of vanadium precipitates, resulting in the uniform distribution of hydrogen and reduction of hydrogen accumulated at local grain boundaries, which promotes the inhibition of hydrogen-induced cracking.

Evaluation of Susceptibility to Hydrogen Embrittlement—A Rising Step Load Testing Method

Hydrogen embrittlement (HE) is a dangerous reaction that puzzled the material world for a long time. Hydrogen embrittlement is a type of deterioration which can be linked to corrosion and corrosion-control processes. It involves the introduction of hydrogen into a component, an event that can seriously reduce the ductility and load-bearing capacity, cause cracking and catastrophic brittle failures at stresses below the yield stress of susceptible materials. Presently this phenomenon is not completely understood and hydrogen embrittlement detection, in particular, seems to be one of the most difficult aspects of the problem. Although the process cannot be understand completely, method such as baking can reverse the process of hydrogen embrittlement and RSL (Rising Step Load) testing presents an excellent way to test the susceptibility to hydrogen embrittlement in the steel and its alloys. Different specimens were made to facilitate the testing. This study determines the effect of coating process have on the brittleness of the material and use of RSL (Risisng Step Load) mechanical loading test method to qualify plating processes for the risk of internal hydrogen embrittlement. The paper introduces the different causes of the hydrogen embrittlement, especially the zinc coating process and the hot dip galvanizing process. Subsequently, hydrogen embrittlement prevention and testing are discussed, as well as the current McGill-established RSL (Rising Step Load) bend testing’s principle, potential set-up, tested specimens and some of the critical results. Finally, some of the future development of the hydrogen embrittlement prevention will be covered.

Effects of Hydrogen Charging Time and Pressure on the Hydrogen Embrittlement Susceptibility of X52 Pipeline Steel Material

The effects of hydrogen charging time and pressure on the hydrogen embrittlement(HE)susceptibility of X52 pipeline steel material are studied by slow strain rate tensile tests.The fracture morphologies of the specimens are observed by scanning electron microscopy.The HE susceptibility of the X52 pipeline steel material increases with an increase in both hydrogen charging time and hydrogen pressure.At a charging time of 96 h,the HE susceptibility index reaches 45.86%,approximately 3.6 times that at a charging time of 0 h.Similarly,a charging pressure of 4 MPa results in a HE susceptibility index of 31.61%,approximately 2.5 times higher than that at a charging pressure of 0.3 MPa.

Review on the design of high-strength and hydrogen-embrittlement-resistant steels

Given the carbon peak and carbon neutrality era,there is an urgent need to develop high-strength steel with remarkable hydrogen embrittlement resistance.This is crucial in enhancing toughness and ensuring the utilization of hydrogen in emerging iron and steel materials.Simultaneously,the pursuit of enhanced metallic materials presents a cross-disciplinary scientific and engineering challenge.Developing high-strength,toughened steel with both enhanced strength and hydrogen embrittlement(HE)resistance holds significant theoretical and practical implications.This ensures secure hydrogen utilization and further carbon neutrality objectives within the iron and steel sector.Based on the design principles of high-strength steel HE resistance,this review provides a comprehensive overview of research on designing surface HE resistance and employing nanosized precipitates as intragranular hydrogen traps.It also proposes feasible recommendations and prospects for designing high-strength steel with enhanced HE resistance.

Hydrogen Embrittlement of Advanced High-Strength Steel for Automobile Application:A Review

The hydrogen embrittlement(HE)fracture of advanced high-strength steels used in lightweight automobiles has received increasing public attention.The source,transmission,and movement of hydrogen,characterization parameters,and test methods of HE,as well as the characteristics and path of HE fractures,are introduced.The mechanisms and modes of crack propagation of HE and hydrogen-induced delayed fracture are reviewed.The recent progress surrounding micro and macro typical fracture characteristics and the influencing factors of HE are discussed.Finally,methods for improving HE resistance can be summarized as follows:(1)reducing crystalline grain and inclusion sizes(oxides,sulfides,and titanium nitride),(2)controlling nano-precipitates(niobium carbide,titanium carbide,and composite precipitation),and(3)increasing residual austenite content under the reasonable tension strength of steel.

Review on Hydrogen Embrittlement of Press-hardened Steels for Automotive Applications

Press-hardened steel(PHS)with an ultimate tensile strength(UTS)of 1500 MPa has been widely used in automotive body-in-white in the last two decades,due to its ultra-high strength and excellent formability that is achieved by hot stamping process.However,the application of PHS with UTS exceeding 1500 MPa in automotive industry could be deferred due to the increased risk of hydrogen embrittlement.To reduce this kind of risk,recent research efforts have been focused on various ways to optimize the microstructure of PHS.The present review intends to summarize these efforts,to highlight present solutions to address hydrogen embrittlement,and to shed light on directions for future improvement.The influence of microstructure on the hydrogen embrittlement of PHS has been discussed in terms of both the steel substrate and the surface condition.The substrate part covers the influence of martensite,carbides,inclusions,and retained austenite,while the surface part covers decarburization and oxidation,pre-coating,and trimming.

Assessment of Hydrogen Embrittlement Susceptibility and Mechanism(s)in Quench and Tempered AISI 4135 Steel Using A Novel Fast Fracture Test in Bending

A newly proposed rapid fracture test in four-point bending was used to evaluate the effect of tempering on the hydrogen embrittlement(HE)susceptibility of an AISI 4135 steel,where it was tempered to four different strength(or hardness)levels.It was observed that HE susceptibility increases with the increase in hardness.It was shown that there will be minimal impact of hydrogen(H)on the fracture of materials with hardness 37 HRC and below,even if they are completely saturated with H.On the other hand,H will have similar detrimental effect on fracture properties of quench and tempered(Q and T)steels having hardness higher than 45 HRC.Ductile to brittle transition behavior was observed for a critical hardness(or strength)range as well as for a critical concentration level of H.Additionally,a critical H concentration was observed to exist for each of the strength levels.Fractography was performed in addition to microstructural characterization using transmission electron microscopy(TEM).A very good correlation was observed between the fast fracture test results and fractography.The fast fracture test was further compared with a conventional incremental step load(ISL)test for the evaluation of HE susceptibility.The ISL test results and fracture surface characteristics corroborate very well with the observations from the fast fracture test.This study successfully establishes the fast fracture test as a novel technique to study HE susceptibility and mechanism(s).

Ab Initio Investigations for the Role of Compositional Complexities in Affecting Hydrogen Trapping and Hydrogen Embrittlement:A Review

ydrogen embrittlement(HE)seriously restricts the service safety of structural metallic materials applicate in aerospace,ocean,and transportation.Recent studies aiming at increasing the HE-resistance have been focusing on trapping diffusible H atoms by inherent microstructural features in materials.Alloying-induced compositional complexities,including different types of solute atoms,lattice chemical heterogeneities,and carbide precipitates,have attracted research efforts regarding the H trapping capabilities and potential to reduce the susceptibility to HE.In this paper,we review recent progress in exploiting compositional complexities to regulate the hydrogen trapping characteristics and mechanical properties in H-containing environments.The focus is placed on results and insights from ab initio calculations based on density functional theory(DFT).Quantitative predictions of trapping parameters and atomic scale details that are hardly to be gained through traditional experimental characterizations are provided.Additionally,we overview the electronic/atomistic mechanisms of H trapping energetics in metallic materials.Finally,we propose some key challenges and prospects in simulation of defect interactions,interpretation of experimental characterizations,and developing microstructure-based H diffusion prediction models.For the applications of first principle calculations,we illustrate how the DFT data can complement experimental characterizations to guide composition and microstructure design for better HE-resistant materials.

Enhancing the Hydrogen Embrittlement Resistance of Medium Mn Steels by Designing Metastable Austenite with a Compositional Core-shell Structure

Deformation-induced martensite transformation from metastable retained austenite is one of the most efficient strain-hardening mechanisms contributing to the enhancement of strength-ductility synergy in advanced high-strength steels.However,the hard transformation product(often-martensite)and the H redistribution associated with phase transformation essentially decrease materials’resistance to hydrogen embrittlement.To solve this fundamental conflict,we introduce a new microstructure architecting strategy based on an accurately design of core–shell compositional distribution inside the austenite phase.We employed this approach in a typical medium Mn steel(8 wt.%Mn)with an ultrafine grained austenite-ferrite microstructure.We produced a high Mn content(15–16 wt.%)in the austenite shell region and a low Mn content(~12 wt.%)in the core region,through a thermodynamics-guided two-step austenite reversion treatment.During room-temperature deformation,the austenite core transforms continuously starting from a low strain,providing a high and persistent strain-hardening rate.The transformation of Mn-rich austenite shell,on the other hand,occurs only at the latest regime of the deformation,thus effectively inhibiting the nucleation of H-induced cracks at ferrite/deformation-induced martensite interfaces as well as suppressing their growth and percolation.This step-wise transformation,tailored directly targeted to protect the hydrogen-sensitive microstructure defects(interfaces),results in a significantly enhanced hydrogen embrittlement resistance without sacrificing the mechanical performance in hydrogen-free condition.The design of compositional core–shell structure is expected to be applicable to,at least,other multiphase advanced high-strength steels containing metastable austenite.

Competitive role of film-like austenite and transition carbides on hydrogen embrittlement resistance and impact toughness in bainite-containing quenched and partitioned steel

A microstructure composed of martensite matrix,lower bainite,and stable film-like austenite was designed by a quenching and isothermal bainitic holding process in a 0.30C–2.69Mn–1.71Si(wt.%)steel.The yield strength,tensile strength,and ductile-to-brittle transition temperature(DBTT)of the high-strength steel thus obtained were 1263 MPa,1521 MPa,and-33℃,respectively,and at-20℃,it showed superior low-temperature toughness,which reached 77.5 J/cm^(2).Meanwhile,it showed excellent hydrogen embrittlement(HE)resistance,and the total elongation loss is only 3.1%after 15 min of hydrogen charging.The excellent comprehensive performance is attributed to the fact that fine stable austenite with film-like morphology hindered the crack nucleation and propagation,and hindered hydrogen diffusion as a hydrogen trap.However,with a decrease in the isothermal temperature,transition carbide precipitation was accompanied by a further decrease in austenite grain size.For this condition,although transition carbides can act as effective hydrogen traps,excessive precipitation decreased the carbon content of retained austenite and increased the deformation heterogeneity between austenite and martensite matrix,leading to weakened austenite stability and HE resistance,a total elongation loss of approximately 39%(15 min hydrogen charging),a sharp decrease in impact toughness,and an increase in DBTT.The competitive role of film-like austenite and transition carbides on the comprehensive mechanical performance of steel is revealed,especially the suppression of crack nucleation and propagation that will provide a guide for the design of high strength steels with excellent impact toughness and HE resistance.

Enhanced Hydrogen Embrittlement Resistance via Cr Segregation in Nanocrystalline Fe-Cr Alloys

Hydrogen is a clean fuel with numerous sources,yet the hydrogen industry is plagued by hydrogen embrittlement(HE)issues during the storage,transportation,and usage of hydrogen gas.HE can compromise material performance during service,leading to significant safety hazards and economic losses.In the current work,the influence of element Cr on the HE resistance of nanocrystalline Fe-Cr alloys under different hydrogen concentrations and strain rates was evaluated.With hybrid Monte Carlo(MC)and molecular dynamics(MD)simulations,it was found that Cr atoms were segregated at grain boundaries(GB)and inhibited the GB decohesion.Correspondingly,Cr segregation improved the strength and plasticity of the nanocrystalline Fe-Cr alloys,especially the HE resistance.Moreover,the Cr segregation reduced the diffusion coefficient of hydrogen and inhibited hydrogen-induced cracking.This work provided new insight into the development of iron-based alloys with high HE resistance in the future.