Cr is used to increase corrosion resistance in steels or nickel-based superalloys. Assuming you are chromizing a steel part in pure Cr gas (and thus the surface concentration remains constant), how long will it take at 980C to bring the Cr concentration in your hardware to 1.8 at.%, at a distance of 20 m below the surface? Use Do = 0.54 cm^2 /s and EA = 286 kJ/mol.