Einfluß der plastischen Verformung auf das Diffusions‐ und Löslichkeitsverhalten von Wasserstoff in Austenitischen Fe‐ und Ni‐Basislegierungen

Abstract

Es wird das Diffusions-und Loslichkeitsverhalten von Wasserstoff in den hochlegierten austenitischen Werkstoffen 2.4816, 2.4642, 1.4558, 1.4541 im unverformten und bis zu 50% kaltverformten Zustand mit einer elektrochemischen Permeationsmethode und Wasserstoffanalysenmefitechnik (LECO RH 402) untersucht .Mit steigendem Nickelgehalt wird eine Zunahme der Diffusionskoeffizienten, cine Abnahme der Aktivierungsenergien und eine Abnahme der Loslichkeit beobachtet. Eine Kaltverformung der Werkstoffe fuhrt in Abhangigkeit von der Zusammensetzung zu einem veranderten Diffusionsverhalten. Im Werkstoff 1.4541 kommt es infolge von Martensitbildung zu einer Erhohung des Diffusionskoeffizienten um 2 GroBenordnungen. Bei den anderen Werkstoffen fiihrt die Kaltverformung zu einer Erniedrigung des Diffusionskoeffizienten max. urn den Faktor 2,7 und zu hoheren Restwasserstoffgehalten nach Effusion des gelosten Wasserstoffs. Als Ursache werden Trapvorgange an Versetzungskernen und an den wahrend der Beladung entstandenen Rissen angesehen.The measurements of diffusivity and solubility were performed on as received and up to 50% cold worked high alloyed austenitic materials Inconel 600, Inconel 690, Incoloy 800 and AISI 321 by means of an electrochemical permeation method and a hydrogen determination technique (LECO R H 402).With increasing nickel content of the materials the hydrogen diffusivity increases whereas the activation energy of diffusion and the hydrogen solubility decrease.A marked change of the diffusion behaviour is observed in the case of cold worked samples depending on the alloy composition. An increase of diffusivity by about two orders of magnitudes was measured for AISI 321 as a result of a-martensite transformation.The cold working of the other alloys results in a decrease of the diffusivity by a factor of 2.7 maximally and a higher hydrogen content after effusion of the solved hydrogen. This refers to a higher hydrogen trapping. It is assumed that hydrogen atoms are trapped at the cores of dislocations and at microcracks formed during charging. * Dr. rer. nat. K. Murnrnert, Dip1.-Chem. M . Uhlernann, Dr. rer. nat. H.-J. Engelmann Institut fur Festkorper-und Werkstofforschung Dresden e.V

Hydrogen Diffusion in Austenitic Stainless Steels

“…The apparent activation energies for diffusion include the activation energy for lattice diffusion and different binding states of hydrogen at the traps, being assumed that the ratios of lattice diffusivities to apparent diffusivities are in the same range of 1.9, as reported by Uhlemann et al [19] for the Cr 30 Ni 59 and Cr 21 Ni 35 alloys. The calculated data agree well with the literature values determined for lattice diffusion in austenitic stainless steels [14][15][16]18,[20][21][22]. The present results shown in Fig.…”

“…The highest diffusivity was determined for the alloy Cr 30 Ni 36, which can be clearly attributed to the high nickel content. It is known that with increasing nickel content the diffusion coefficient increases and the mechanical stability decreases [22]. The lowest hydrogen diffusion of all alloys was found for the steel Cr 17 Ni 9.5 (see Table 1), and again is clearly attributed to the low nickel content.…”

Scanning AES and chemical investigation of materials failure due to phosphorus and sulphur grain boundary segregation in type AISI 304L stainless steel

“…A relatively low cathodic current density was applied to avoid a high hydrogen concentration in the lattice compared to grain boundaries [17]. The binding energy of hydrogen for steels at grain boundaries was found to be 58.6 kJ Á mol À1 [18], which is only a small difference from the binding energy of diffusivity to interstitional sites within the grains (54.8 kJ Á mol À1 ) [19,20]. The higher intergranular fracture part of HT samples compared to SA samples may be explained by the properties of metalloid elements, like As, P and S, to poison the hydrogen adatom-adatom combination step.…”

“…The penetration depth of hydrogen can be calculated by the value of the diffusion coefficient [19]. During charging of 14 days at room temperature the material is penetrated by hydrogen 30 lm, whereas after exposure to 50 8C in the furnace for 10 days a value of 90 lm is reached.…”