Studies of nitrogen formation in four iron alloys after room temperature N + implantation are carried out by using an X-ray diffractometer. Measures are taken to improve the effectiveness of the X-ray method when applied to a thin surface layer. The method is convenient and straightforward. All equilibrium nitrides are observed in the implanted layer. It is shown that with increasing fluences the nitrides appear in the order of γ', ∊ and ξ. Their relative amounts undergo changes upon annealing. These observations are in accordance with the trend towards equilibrium. Diffraction peaks of the nitrides reduce their intensity as the surface layer is gradually worn away in a wearing test. However, the wear resistance of the implanted layer appears unchanged even long after disappearance of the peaks of nitrides.