Bear in mind that iron rusts differently from steel. Iron will form a layer of surface rust and stop there, the oxidation having sealed the underlying iron away from a source of oxygen. No oxygen, no rust. So if you decide to remove the layer of rust and hope to prevent any more from growing, you must remove all the rust and seal it with a very tough paint.
A better idea might be to simply paint over the rust. Since the rust itself has sealed the iron and will not "grow" any further, the paint will remain in place.
-Ryan