EXAFS investigation of low temperature nitrided stainless steel

Low temperature nitrided stainless steel AISI 316 flakes were investigated with EXAFS and X-ray diffraction analysis. The stainless steel flakes were transformed into a mixture of nitrogen expanded austenite and nitride phases. Two treatments were carried out yielding different overall nitrogen contents: (1) nitriding in pure NH3 and (2) nitriding in pure NH3 followed by reduction in H2. The majority of the Cr atoms in the stainless steel after treatment 1 and 2 was associated with a nitrogen–chromium bond distance comparable to that of the chemical compound CrN. The possibility of the occurrence of mixed substitutional– interstitial atom clusters or coherent nitride platelets in nitrogen-expanded austenite is discussed.