Nitriding behavior of Fe–4wt%V and Fe–2wt%V alloys

The nitriding behavior of Fe–4wt%V and Fe–2wt%V alloys was investigated by exposing these alloys to a gas mixture of ammonia and hydrogen at 580 °C. The microstructure of the nitrided specimens was analyzed employing light and scanning electron microscopy, hardness measurements, and X-ray diffraction. To determine the elemental composition of the nitrided zone electron probe microanalysis (EPMA) was applied. The nitrided zone of the Fe–4wt%V specimens comprised many grains exhibiting a lamellar morphology characterized by a lamellar spacing of 20–40 nm. Such a lamellar microstructure was absent in the nitrided zone of the Fe–2wt%V specimens. These morphological results, together with the obtained hardness and X-ray diffraction data, demonstrate that a discontinuous coarsening reaction occurs in nitrided Fe–4wt%V alloy. Such a reaction was not observed before for nitrided Fe–V alloys. EPMA showed the uptake of excess nitrogen in the nitrided zone. The discontinuously transformed regions contain less nitrogen than the not transformed regions. The effect of these phenomena on the nitriding kinetics was analyzed and discussed.