Steel-type Pokémon are made of, or coated with, steel. [1]
Steel type pokemon, along with Rock Pokémon and Ground Pokémon are three types that represent earth's minerals (all three are immune to the Sandstorm weather condition) with steel representing metal. Steel pokemon are known for their resilance and strength.
Magnemite and Magneton were the first pokemon to be reclassified from a single-type (Electric Pokémon) to a Steel/Electric dual-type.
To date, there are 5 single-steel-type pokemon.