In this research, titanium nitride thin films were deposited by reactive DC magnetron sputtering with two original constraints imposed by the expected industrial application as roll to roll decorative coating of steel: the samples should be connected to earth and should not be heated during deposition. Previous work has shown that low N-2 atmospheres should be maintained during sputtering processes in order to obtain a colour range from grey to gold, In this study, the nitrogen content measured by Resonant Nuclear Reaction Analysis and the crystal structure revealed by glancing angle X-ray diffraction, were used to determine the coating composition. The appearance presented in CIE L*a*b* colour coordinates and the micro-hardness obtained with a Berkovitch nano-indenter were also evaluated for all the films. Results obtained with the TiNx layers deposited on monocrystalline polished silicon were then compared to coating physical properties measured on polycrystalline iron (alpha-Fe) substrates. Only the coating produced under the lowest N-2 gas flow exhibits a different nitrogen content on both substrates resulting in an hexagonal phase on iron. Colour differences appear and are probably due to different substrate roughness. Hardnesses between 12 and 22 GPa are obtained on both substrates. Such results tend to qualify this process for possible industrial application as a protective coating with a pleasant appearance.