The corrosion resistance of carbon steel in a harsh environment was improved by preparing a chromized coating on the surface through the method of pack cementation. Nano rare earth‐oxides (NREOs), Y2O3, CeO2, and La2O3 were added to the pack and to further enhance the performance of the chromized coatings. Morphological results showed that NREO refined the microstructure of chromized coatings by retarding the growth of grains. The Mott–Schottky plots demonstrated that coating Cr–La2O3 displayed fewer defects than the other two composite coatings, which was beneficial to reduce the corrosion tendency. In addition, the potentiodynamic polarization and impedance spectroscopy analysis showed that the order of the corrosion rates of the achieved coatings was pure Cr > Cr–Y2O3 > Cr–CeO2 > Cr–La2O3, which revealed that the corrosion resistance increased accordingly.