Nitrocarburizing of pure iron samples is achieved at 853 K and is easily controlled by introducing C3H8 in the afterglow of a flowing microwave Ar-N-2-H-2 plasma. The carbon uptake in the solid is actually possible with methane but strongly limited. The use of propane enhances the carbon flux and the Flat configuration is synthesized for the first time by this kind of process. For this stack, diffusion paths in the ternary system determined from chemical analyses by secondary neutral mass spectrometry reproduce satisfactorily X-ray diffraction results which only reveal, as optical micrographs, epsilon and alpha phases. Propane offers an accurate control of the nitrocarburizing conditions. As an example, a modulation of N and C contents in iron could be achieved to create new carbonitride multilayers. (c) 2005 Elsevier B.V All rights reserved.