20 keV N+ions have been implanted on57Fe enriched Fe films and RF deposited on glass and NaCl substrates with various fluences up to 3.0×1016N+/cm2. Conversion electron Mossbauer spectroscopy and transmission electron microscopy measurements performed at room temperature on the as‐implanted samples reveal the presence of &agr;‐Fe, &agr;′‐martensite, and &egr;‐Fe3−xN phases. &agr;″‐Fe16N2is only detected after a subsequent annealing at 220 °C; &agr;′‐martensite with a low nitrogen content appears as the precursor of &agr;″, The additional nitrogen content needed for this process is supplied by the &egr; phase. ©1995 American Institute of Physics.