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13 Avril 2012 - A. Martinavicius - Structural property changes in austenitic stainless steel induced by nitrogen incorporation

par LABGPM - publié le

Vendredi 13 Avril 2012 - 10h

Structural property changes in austenitic stainless steel induced by
nitrogen incorporation.

Abstract :

Nitriding of austenitic stainless steel (ASS) at moderate temperatures
( 400°C) leads to the formation of a modified layer which shows
increased hardness and induced magnetism without compromising the
corrosion resistance. The nature of the near-surface nitrided layer
produced by low-temperature ( 400°C) plasma-assisted nitriding of 304L
is studied. A combination of global probes (X-ray diffraction (XRD),
nuclear reaction analysis, glow discharge optical emission spectroscopy)
and local probes (field ion microscopy, atom probe tomography, X-ray
absorption near edge structure and extended X-ray absorption fine
structure spectroscopies) is employed to reveal the morphology, phase
structure, atomic ordering and chemical state. While only a single
phase, usually called the S phase or expanded austenite, can be detected
by the X-ray diffraction local probes consistently reveal the
heterogeneous nature of this phase consisting of nanometric CrN
precipitates embedded in a Fe4N-like matrix. These observations suggest
that incorporation of large amounts of N provides strong driving force
for CrN formation even at 400°C, a rather low temperature.