Mechanism of Hydrogen Embrittlement of Austenitic Steels (original) (raw)
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Diagnostic experimental results on the hydrogen embrittlement of austenitic steels
Acta Materialia, 2003
Three main available hypotheses of hydrogen embrittlement are analysed in relation to austenitic steels based on the studies of the hydrogen effect on the interatomic bonds, phase transformations and microplastic behaviour. It is shown that hydrogen increases the concentration of free electrons, i.e. enhances the metallic character of atomic interactions, although such a decrease in the interatomic bonding cannot be a reason for brittleness and rather assists an increased plasticity. The hypothesis of the critical role of the hydrogen-induced ⑀ martensite was tested in the experiment with the hydrogen-charged Si-containing austenitic steel. Both the fraction of the ⑀ martensite and resistance to hydrogen embrittlement were increased due to Si alloying, which is at variance with the pseudo-hydride hypothesis. The hydrogencaused early start of the microplastic deformation and an increased mobility of dislocations, which are usually not observed in the common mechanical tests, are revealed by the measurements of the strain-dependent internal friction, which is consistent with the hypothesis of the hydrogen-enhanced localised plasticity. An influence of alloying elements on the enthalpy E H of hydrogen migration in austenitic steels is studied using the temperature-dependent internal friction and a correlation is found between the values of E H and hydrogen-caused decrease in plasticity. A mechanism for the transition from the hydrogen-caused microplasticity to the apparent macrobrittle fracture is proposed based on the similarity of the fracture of hydrogenated austenitic steels to that of high nitrogen steels.
Mechanisms of Hydrogen Embrittlement of Austenitic Stainless Steels
Journal of the Mechanical Behavior of Materials, 2005
Based on the experimental studies of interatomic bonds, hydrogen-induced phases and hydrogen effect on dislocation properties, mechanisms of hydrogen embrittlement are analysed in relation to austenitic steels. It is shown that neither hydrogen decohesion nor pseudo-hydrides can be responsible for hydrogen degradation, whereas the HELP hypothesis is confirmed by Η-caused decrease in the start stress of dislocation sources and increased mobility of dislocation. Hydrogen-increased concentration of free electrons is considered as important reason for change of dislocation properties. A mechanism is proposed for localisation of Henhanced plastic deformation due to the Η-increased concentration of thermodynamically equilibrium vacancies, which finally results in macrobrittle fracture.
Hydrogen environment embrittlement of stable austenitic steels
International Journal of Hydrogen Energy, 2012
ABSTRACT Seven stable austenitic steels (stable with respect to γ → α′ transformation at room temperature) of different alloy compositions (18Cr–12.5Ni, 18Cr–35Ni, 18Cr–8Ni–6Mn–0.25N, 0.6C–23Mn, 1.3C–12Mn, 1C–31Mn–9Al, 18Cr–19Mn–0.8N) were tensile tested in high-pressure hydrogen atmosphere to assess the role of austenite stability on hydrogen environment embrittlement (HEE). The influence of hydrogen on tensile ductility was small in steels that are believed to have a high initial portion of dislocation cross slip (18Cr–12.5Ni, 18Cr–35Ni, 18Cr–8Ni–6Mn–0.25N), while the effects of hydrogen were significantly greater in steels with other primary deformation modes (planar slip in 18Cr–19Mn–0.8N and 1C–31Mn–9Al or mechanical twinning in 0.6C–23Mn and 1.3C–12Mn) despite comparable austenite stability at the given test conditions. It appears that initial deformation mode is one important parameter controlling susceptibility to HEE and that martensitic transformation is not a sufficient explanation for HEE of austenitic steels.
Hydrogen embrittlement of low carbon structural steel at macro-, micro-and nano-levels
International Journal of Hydrogen Energy, 2020
The hydrogen embrittlement (HE) behavior of low carbon steel was investigated. Hydrogen-rich acidic corrosive environments were used, and their effects analyzed. Hydrogen assisted cracking, blister, and grain boundary deterioration were detected. Nanoelastic and nanomechanical properties changes due to HE were investigated. Nanoelastic modulus reduced to 45% in some of the grains due to HE. Low carbon steel Hydrogen-assisted cracking Hydrogen embrittlement Corrosion Elastic modulus and Nanomechanical properties a b s t r a c t This paper aims to investigate the effect of hydrogen-induced mechanical degradation of low carbon steel at macro-, micro-and nano-levels in the hydrogen-rich acidic environments. From the test results of specimens, a relationship in hydrogen concentration and corrosion propagation was observed that led to the significant reductions of bulk elastic modulus after 28 days of exposure to the hydrogen-rich acidic environments. Through microstructural analysis, the deformation of larger grains, cracks, and blisters caused by hydrogen penetration was found as the possible cause for this reduction. Moreover, by performing nanoindentation on the areas of interest of various specimens at planned time periods, the influence of hydrogen on the nano-elastic and nano-hardness properties of grains was determined. The 3D surface profiles of the nano-elastic modulus and nano-hardness of various specimens are presented in this paper.
A Mechanism for Hydrogen Embrittlement in Martensitic Steel Based on Hydrogen Dilation
2022
Martensitic steels are used at a wide range of strength levels in environments which expose them to hydrogen or water vapor over a large range of partial pressures and temperatures. Hydrogen can cause catastrophic failures under many seemingly benign conditions. The effect of hydrogen on the dimension stability of high strength martensitic steels under such conditions has been poorly understood, and existing models do not seem to adequately account for it. Experiments were conducted to measure the variation in volume due to the uptake of hydrogen of such steels under near-ambient conditions, and the results were compared to theoretical estimates derived from the density of defects acting as hydrogen traps. Based on these results a new model for hydrogen embrittlement was developed. The hydrogen lattice dilation (HLD) model isolates volume expansion as a primary driver of hydrogen embrittlement. It provides and distinguishes two modes of failure acceleration: the fast, brittle, stress-intensity independent cracking under higher static crack loading, and a slower, highly stress-intensity dependent tearing mode at lower stress intensity. The relationship between the two is explained, as is how hydrogen absorption by defects accounts for the crack threshold and crack velocity of each.
Hydrogen Embrittlement of Low Carbon Structural Steel
Procedia Materials Science, 2014
""Hydrogen embrittlement (HE) of steels is extremely interesting topic in many industrial applications, while a predictive physical model still does not exist. A number of studies carried out in the world are unambiguous confirmation of that statement. Bearing in mind multiple effects of hydrogen in certain metals, the specific mechanism of hydrogen embrittlement is manifested, depending on the experimental conditions. In this paper structural, low carbon steel, for pressure purposes, grade 20 - St.20 (GOST 1050-88) was investigated. Numerous tested samples were cut out from the boiler tubes of fossil fuel power plant, damaged due to high temperature hydrogen attack and HE during service, as a result of the development of hydrogen-induced corrosion process. Samples were prepared for the chemical composition analysis, hardness measurement, impact strength testing (on instrumented Charpy machine) and microstructural characterization by optical and scanning electron microscopy - SEM/EDX. Based on multi-scale special approach, applied in experimental investigations, the results, presented in this paper, indicate the simultaneous action of the hydrogen-enhanced decohesion (HEDE) and hydrogen enhanced localized plasticity (HELP) mechanisms of HE, depending on the local concentration of hydrogen in investigated steel. These results are consistent with some models proposed in literature, about a possible simultaneous action of the HELP and HEDE mechanisms in metallic materials.
Overview of hydrogen embrittlement in high-Mn steels
International Journal of Hydrogen Energy, 2017
Hydrogen and fuels derived from it will serve as the energy carriers of the future. The associated rapidly growing demand for hydrogen energy-related infrastructure materials has stimulated multiple engineering and scientific studies on the hydrogen embrittlement resistance of various groups of high performance alloys. Among these, high-Mn steels have received special attention owing to their excellent strength e ductility e cost relationship. However, hydrogen-induced delayed fracture has been reported to occur in deep-drawn cup specimens of some of these alloys. Driven by this challenge we present here an overview of the hydrogen embrittlement research carried out on high-Mn steels. The hydrogen embrittlement susceptibility of high-Mn steels is particularly sensitive to their chemical composition since the various alloying elements simultaneously affect the material's stacking fault energy, phase stability, hydrogen uptake behavior, surface oxide scales and interstitial diffusivity, all of which affect the hydrogen embrittlement susceptibility. Here, we discuss the contribution of each of these factors to the hydrogen embrittlement susceptibility of these steels and discuss pathways how certain embrittlement mechanisms can be hampered or even inhibited. Examples of positive effects of hydrogen on the tensile ductility are also introduced.
Electronic effect on hydrogen brittleness of austenitic steels
Journal of Applied Physics, 2010
Hydrogen effects in austenitic steels are studied using the ab initio calculations of the electronic structure, conduction electron spin resonance, internal friction, and mechanical tests. It is shown that the hydrogen-caused elastic shielding of dislocations is not sufficient for interpretation of hydrogen-enhanced localized plasticity ͑HELP͒. Similar effects of hydrogen and nitrogen and the opposite effect of carbon on dislocation mobility are demonstrated, which cannot be explained within the framework of continuum mechanics. An interpretation of hydrogen embrittlement in terms of the hydrogen-increased concentration of free ͑conduction͒ electrons is proposed. Based on the electronic approach to the HELP phenomenon, practical recommendations for increase in hydrogen resistance of austenitic steels are made and tested.
Engineering Fracture Mechanics, 2019
Component failures due to the hydrogen embrittlement (HE) were observed in different industrial systems, including high-pressure hydrogen storage tanks, aircraft components, high-strength alloy components, and high-strength steel fasteners. The contemporary approach in studying the effects of hydrogen on the mechanical properties of steels and iron at different scales is based on the implementation of various multiscale (macro, micro-meso, and nano-atomic) modeling approaches and the applications of advanced experimental methods. A large number of contemporary studies confirmed the multiple effects and activity of different HE mechanisms in steels and iron. The coexistence and synergistic activity-concurrent action and effects in a cooperative manner of different HE mechanisms, including the hydrogen-enhanced localized plasticity (HELP) and the hydrogen-enhanced decohesion (HEDE), were recently detected and confirmed through computations-simulations, as well as experimentally in different grades of steel. However, the critical evaluation and quantification of synergy between the HELP and HEDE mechanisms, enhanced plasticity and decohesion, hydrogen-deformation/dislocation interactions and their simultaneous effect on the mechanical properties (hardening and softening), still do not exist. In this review paper, the multifaceted nature of the synergistic interplay of HE mechanisms is covered through extensive literature overview regarding the chronological development of ideas related to the HELP + HEDE concept and HELP mediated HEDE model. The particular emphasis is given to the proposal of the novel and unified HELP + HEDE model based on the specific microstructural mapping of the dominant HE mechanisms with implications on the fracture process and resulting hydrogen-assisted fracture modes. Most of up-to-date experimental and modeling approaches, current trends and future challenges in the investigation of the synergistic interplay of HE mechanisms in different grades of steel, including the most advanced, and iron, are also included and critically discussed.
On a role of hydrogen-induced ɛ-martensite in embrittlement of stable austenitic steel
Scripta Materialia, 2003
Effect of the hydrogen-caused c ! e transformation on hydrogen embrittlement (HE) of AISI 310 type austenitic steel is studied. Using the alloying with silicon that increases the fraction and stability of the hydrogen-induced emartensite, it is shown that the resistance to HE is improved. It is concluded that other factors, among them the activation enthalpy of hydrogen migration, are crucial for HE.