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


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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