Thin CrN/AlMgSiN films with a composition of 30.6Cr-11.1Al-7.3Mg-1.2Si-49.8N (at.%) were deposited on steel substrates in a cathodic arc plasma deposition system. They consisted of alternating crystalline Cr-N and AlMgSiN nanolayers. During oxidation at 800 degrees C for 200 h in air, a thin oxide layer was formed by outward diffusion of Cr, Mg, Al, Fe, and nitrogen, and inward diffusion of oxygen. Silicon was relatively immobile at 800 degrees C. The oxidation at 900 degrees C for 10 h in air resulted in the formation of a thin Cr2O3 layer containing dissolved ions of Al, Mg, Si, and Fe. Silicon became mobile at 900 degrees C. The oxidation at 900 degrees C for 50 h in air resulted in the formation of a thin SiO2-rich layer underneath the thin Cr2O3 layer. The film displayed good oxidation resistance. The main factor that decreased the oxidation resistance of the film was the outward diffusion and subsequent oxidation of Fe at the sample surface, particularly along the coated sample edge. (C) 2013 Elsevier B. V. All rights reserved.