Anisotropy effects on gaseous nitriding of austenitic stainless steel single crystals

Ömer C. Kücükyildiz, Flemming B. Grumsen, Thomas L. Christiansen, Grethe Winther, Marcel A.J. Somers*

*Corresponding author for this work

    Research output: Contribution to journalJournal articleResearchpeer-review

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    Low temperature nitrided austenitic stainless steel exhibits strong orientation dependent case growth kinetics. Anisotropy effects during low temperature gaseous nitriding of single crystals of austenitic stainless steel with surface-normal orientations 〈100〉, 〈111〉 and 〈10 7 2〉 were investigated with thermogravimetry, X-ray diffractometry (XRD), glow discharge optical emission spectroscopy (GD-OES), nano-indentation and electron back-scatter diffraction (EBSD). Case growth kinetics were fastest for 〈100〉 and slowest for 〈111〉. Depth-profiling over the case depth was accomplished by successive layer removal combined with X-ray diffraction and nano-indentation. The results indicate that anisotropic case-growth kinetics is related to early nucleation of long-range ordered (LRO) over-stoichiometric γ’N−Me4N1+ x (Me=metal atoms) in 〈100〉, which is inseparable from short range ordered (SRO) expanded austenite, γN. Depth ranges of elasto-plastic and purely plastic accommodation of the nitrogen induced lattice expansion were distinguished. In the elasto-plastic region stress-gradient enhanced diffusion of N is observed.

    Original languageEnglish
    JournalActa Materialia
    Pages (from-to)168-177
    Publication statusPublished - 2020


    • Anisotropy
    • Expanded austenite
    • Nano-indentation
    • Nitriding
    • Stainless steel


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