Nickel does not rust because rust is iron oxide, and nickel contains no iron. Nickel is naturally corrosion resistant because it forms a thin, stable oxide layer on its surface that helps protect it from further attack. This is one reason nickel is used for plating and as an alloying element in stainless steels and other corrosion resistant alloys.
Nickel can still corrode in certain harsh conditions, such as strong acids, some chloride environments at elevated temperatures, or when it is part of a dissimilar metal pairing that creates galvanic corrosion. If you see rust colored staining on a nickel surface, it is often from iron contamination or nearby steel hardware rather than the nickel itself.
