Oddly enough it takes as much energy for a piece of steel to rust as it did to make it, but the reaction produces its' own energy so it works as long as there is oxygen to react with.

Rust can be arrested by using a type of chemical that transforms it from iron oxide to iron phosphate. I have seen this used in auto restoration in places where you cannot see, like the inside of a door.

But this only slows the rust to a crawl. It will still be eating away at the metal, but it will take a lot more years to show up.