I took that to mean that it is not hot-rolled steel, cold-rolled steel, cast iron, or any other traditional method of converting a lump of iron ore into a usable piece of steel.

It's 1000 km of welding wire welded together. It counts as a new "type" of steel depending on how flexible you are with what counts as different "types".

That is a good point though. Since its just mig wire you could change out the wire at various points to change the properties of the steel.

You could use a combination of stainless and mild steel to write some text on the surface of the bridge.

The surface of the mild steel would rust and the stainless wouldn't!