Filtern
Dokumenttyp
- Zeitschriftenartikel (3) (entfernen)
Sprache
- Englisch (3)
Referierte Publikation
- ja (3)
Schlagworte
- Hydrogen (3) (entfernen)
Hydrogen generally causes lattice distortions and phase transformations when introduced into a metallic crystal lattice. For the investigations reported in this contribution, hydrogen thermal desorption analysis has been carried out to observe the influence of hydrogen desorption on the lattice of super martensitic stainless steel during continuous heating. The lattice expansion parameter and the phase transformations have been monitored during the thermal desorption process, and the influence of hydrogen on such characteristics has been evaluated. It was found that hydrogen has a significant influence on both the lattice parameter and on the thermal expansion. However, hydrogen has no influence on phase transformation during thermal desorption. The hydrogen's desorption behavior in this process was also observed and it turned out that hydrogen desorbs in two stages, i.e., firstly diffusible hydrogen and trapped hydrogen afterward.
Modern methods like carrier gas hot extraction enable the quantification of dissolved hydrogen as well as the determination of the hydrogen trapping and diffusion behavior. This method was applied in order to compare for the first time the hydrogen diffusion and trapping behavior in electrochemically charged and welded duplex stainless steel (1.4462). Characteristic extraction temperatures (400, 650, and 900 °C) were used to quantify the amounts of diffusible hydrogen and trapped hydrogen for the base material and the weld metal, and in order to calculate the effective diffusion coefficients corresponding to the specific temperature. The comparison of the charging methods showed that electrochemically charged samples have a higher content of diffusible hydrogen than the welded samples. In addition, the effusion times increase in welded samples, which indicate a higher amount of trapped hydrogen. In electrochemically charged weld samples, a significant lower concentration of hydrogen was determined than in the base material. In addition, the effective diffusion coefficients were calculated for every microstructure and charging method. It was found that the base material has a higher effective hydrogen diffusion coefficient than that of the weld metal. This effect is due to the tortuous path of hydrogen diffusion in the weld metal.
Neutron radiography and tomography have been used for a time resolved in situ analysis and a 3D mapping of hydrogen diffusion in iron and steel. Samples were electrochemically charged with hydrogen and afterwards neutron transmission images were taken. Hydrogen diffusion coefficients in duplex stainless steel were determined at 623 K by measuring and comparing the sample's mean intensity with a hydrogen-free reference sample and subsequent normalisation to standards with known hydrogen content. In technical iron and in supermartensitic stainless steel the hydrogen distributions have been investigated. The radiographic images in iron show blisters, cracks and the distribution of molecular hydrogen inside cracks. The analysis of the diffusion behaviour of hydrogen out of a blister illustrates the capabilities of the method with respect to time and spatial resolution. The neutron tomography of supermartensitic tensile stressed samples illustrates the capability to visualise hydrogen distributions three-dimensionally. -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
On a utilisé la radiographie neutronique et la tomographie pour une analyse in situ à résolution temporelle et une cartographie 3D de la diffusion de l'hydrogène dans le fer et l'acier. On a chargé des échantillons par électrochimie avec de l'hydrogène et ensuite on a pris des images par émission de neutrons. On a déterminé les coefficients de diffusion de lhydrogène dans l'acier inoxydable duplex à 623 K en mesurant et en comparant l'intensité moyenne de l'échantillon avec un échantillon de référence sans hydrogène et une normalisation subséquente à des échantillons références à teneur connue en hydrogène. On a examiné la distribution d'hydrogène dans le fer technique et dans l'acier inoxydable supermartensitique. Les images radiographiques du fer montrent des soufflures, des fissures, et la distribution de l'hydrogène moléculaire à l'intérieur des fissures. L'analyse du comportement de diffusion de l'hydrogène hors d'une soufflure illustre les possibilités de la méthode par rapport à la résolution temporelle et spatiale. La tomographie neutronique des échantillons supermartensitiques chargés en traction illustre la capacité de visualiser les distributions d'hydrogène en trois dimensions.