Chromium nitride thin films were deposited by unbalanced magnetron (UBM) sputtering on AISI 304 stainless steel. The oxidation behavior of the nitride-coated steel at elevated temperatures ranging from 300 to 800 degreesC in air for 60 min was characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. It was observed that the surface morphology and the color of the specimens oxidized below 500 degreesC remains similar to the as-deposited specimen, and the coating surface was fully covered by a granular oxide layer at 800 degreesC. Unlike the arc ion-plated chromium nitride coatings, the UBM-prepared coatings contain a small amount of beta-Cr2N in the as-deposited specimen besides the CrN phase. Pronounced phase decomposition from CrN into beta-Cr2N occurred at temperature above 500 degreesC and the phase transformation was completed at 800 degreesC. Oxidation of the nitrides to form a Cr2O3 oxide layer was observed in the specimen oxidized above 500 degreesC, and the grain size of both the nitrides and the oxide increases with the oxidation temperature. (C) 2003 The Electrochemical Society.