I use Purple Power first to get as much grease off without damaging the paint. If there's some surface rust, I use Eastwood Fast Etch to immobilize the rust then hit it with acetone make sure it doesn't eat the metal. Then I use Eastwood PRE to prime the surface before painting.
Even if you got no rust, it would still be a good idea to use some metal wash that converts the steel surface to something more resistant to threats of future rust.
Damn, that sounded like some commercial for a bunch of different products...