Hydrogen migration and hydrogen-dislocation interaction in austenitic steels and titanium alloy in relation to hydrogen embrittlement (original) (raw)
Related papers
Acta Materialia, 2010
This paper summarizes recent work at the University of Illinois on the fundamental mechanisms of hydrogen embrittlement. Our approach combines experimental and theoretical methods. We describe the theoretical work on hydride formation and its application to hydrogen embrittlement of Ti alloys through the stress-induced hydride formation and cleavage mechanism, the localization of shear due to solute hydrogen, and finally, we present experimental evidence that favors the decohesion mechanism of hydrogen embrittlement in a β-Ti alloy.
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.
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.
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.
Mechanism of Hydrogen Embrittlement of Austenitic Steels
Materials Science Forum, 2007
Three main hypotheses of hydrogen embrittlement (HE) of austenitic steels are discussed based on the studies of the interatomic interactions, hydrogen-induced phase transformations and dislocations properties. Measurements of electron spin resonance and ab initio calculations of the electron structure witness that the concentration of conduction electrons increases due to hydrogen, which enhances the metallic character of interatomic bonds. The hypothesis of brittle hydrogen-induced phases is disproved by the studies of the silicon-alloyed steels: the silicon-caused increase in the fraction of the εH martensite is accompanied by the decrease of HE. Studies of strain-dependent internal friction have shown the hydrogen-caused decrease in the start stress of microplasticity and increase in the velocity of dislocations in accordance with HELP hypothesis. A mechanism of HELP is proposed based on the hydrogencaused enhancement of the metallic character of interatomic bonds, which results ...
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 effects in X30MnCrN16-14 austenitic steel
Materialwissenschaft und Werkstofftechnik, 2020
Chrome-manganese-nitrogen austenitic steels show a technically relevant combination of proprties, i. e. high strength, high ductility, non magnetic and good corrosion resistance at costs being much lower compared to conventional chrome-nickel austenitic stainless steels which are widely used for hydrogen applications. Hydrogen environment embrittlement of steel X30MnCrN16-14 is investigated by slow displacement rate tensile testing in hydrogen atmosphere at 10 MPa and room temperature. Compared to the values in air, the elongation at fracture as well as the reduction of area are severely reduced in the presence of hydrogen. The microstructure is characterized in detail and the deformation modes are previously reported. It is assumed that the inherent planar deformation modes are facilitated by hydrogen resulting in premature failure. Keywords: Hydrogen embrittlement / austenitic manganese nitrogen steel / microstructure / deformation mechanism / tensile testing
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.