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Abstract
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Chromium-rich nitride precipitates in production of nickelfree austenitic stainless steel plates via pressurised solution
nitriding of Fe–22.7Cr–2.4Mo ferritic stainless steel at 1473 K
(1200 °C) under a nitrogen gas atmosphere was investigated.
The microstructure, chemical and phase composition,
morphology and crystallographic orientation between the
resulted austenite and precipitates were investigated using
optical microscopy, X-ray Diffraction (XRD), Scanning and
Transmission Electron Microscopy (TEM) and Electron Back
Scatter Diffraction (EBSD). On prolonged nitriding, Chromiumrich nitride precipitates were formed frstly close to the surface
and later throughout the sample with austenitic structure.
Chromium-rich nitride precipitates with a rod or strip-like
morphology was developed by a discontinuous cellular
precipitation mechanism. STEM-EDS analysis demonstrated
partitioning of metallic elements between austenite and
nitrides, with chromium contents of about 80 wt.% in the
precipitates. XRD analysis indicated that the Chromium-rich
nitride precipitates are hexagonal (Cr, Mo)2N. Based on the
TEM studies, (Cr, Mo)2N precipitates presented a (1 1 1)γ//
(0 0 2)
(Cr, Mo)2N, [1 1 0 ̄ ]γ//[1 1 0 ̄ ](Cr, Mo)2N orientation relationship
with respect to the austenite matrix. EBSD studies revealed
that the austenite in the regions that have transformed into
austenite and (Cr, Mo)2N have no orientation relation to the
untransformed austenite.
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