Abstract
The formation of a metastable and nitrogen-supersaturated f.c.c.
interstitial solid solution layer on Fe–Cr–Ni austenitic stainless steel
at a moderate temperature around 650–720 K is not entirely understood.
In the present work, three groups of austenitic Fe–Cr–Ni alloys,
containing systematic variations of chromium, nickel and iron contents
were nitrided by plasma-based low-energy ion implantation at 653 K for
4 h and investigated with light-optical microscopy (LOM), electron probe
microanalysis (EPMA), (grazing incidence) X-ray diffraction (XRD) and
transmission electron microscopy (TEM). Commercial AISI 304L was
included for comparison. For the austenitic alloys with a Cr content
below 12 wt.%, a duplex layer is observed in the nitrided case where the
interface between the top layer, consisting of γ'-Fe4N like ordered γ'N, and the disordered γN
(nitrogen enriched austenite) zone underneath is associated with a
decrease in N content. For the alloys with a Cr-content over 12 wt.%, a
featureless continuous zone is observed with LOM and a gradual decrease
in nitrogen content is measured with EPMA. Nevertheless, a similar
duplex structure of outer γ'-Fe4N like ordered γ'N and inner γN
is confirmed by XRD and TEM for all nitrided alloys, irrespective of
the Cr content. The results are discussed in terms of the short-range
order (SRO) promoted by the Cr–N interaction and long-range order (LRO)
caused by the Fe–N interaction.
Original language | English |
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Journal | Acta Materialia |
Volume | 177 |
Pages (from-to) | 35-45 |
ISSN | 1359-6454 |
DOIs | |
Publication status | Published - 2019 |
Keywords
- Austenitic stainless steels
- Isostructurality
- Nitriding
- Order–disorder phenomena
- Phase coexistence