Analysis of information sources in references of the Wikipedia article "Rust" in English language version.
The steel is allowed to rust and because of its alloy composition rusts more slowly than conventional steel and the rust forms a protective coating slowing the rate of future corrosion
For atmospheric corrosion, refer to the Galvanizers Association Millennium Map of average zinc corrosion rates. About 50% of England and Wales has a rate of under 1 μm/year