Thin (40 nm and 160 nm) Cr N coatings were deposited on steel by reactive magnetron sputtering deposition, varying the N 2 flow. The coatings were characterized in the as-deposited condition and after annealing in air at 500 °C for 1 h, by X-Ray Diffraction, Transmission Electron Microscopy, Raman and Fourier Transform Infrared spectroscopies. Hardness was measured by nanoindentation. Coatings have a nanocrystalline microstructure with the phase shifting from Cr 2N to CrN, increasing grain size, thermal stability and resistance to oxidation with increasing N 2. Also intrinsic coating hardness is influenced by both N 2 flow during deposition and film thickness, as a result of changes in phase composition and microstructural properties.