Most acids will remove rust to some extent. Including lemon juice.
http://en.wikipedia.org/wiki/Hydroch...kling_of_steel
Nitric acid is what I use to remove rust from sails. But it will etch ferrous metals including some stainless steels.
Note:
Yes, I know this stuff is danerous. But I've been trained in the use of toxic chemicals and have the proprer safety gear (PPE).