It looks like the steel Pokémon must be made out of one of the aforementioned metals. Steel Pokémon are resistant to 11 types, including normal, rock, steel, ice, grass, flying, fairy, psychic, poison ...
Imports of corrosion resistant flat-rolled steel from the 10 subject countries surged to nearly 2M tons in this year's H1 from less than 1.25M tons a year earlier, impacting the U.S. steel ...