Hi
There is a proviso with using copper sulphate in that the surface to be coated must be totally clean and free of oil and grease etc. This is because there is a chemical reaction where the copper replaces the the top layer of iron of the item being treated. In fact where the copper sulphate solution is applied the item is effectively copper plated, albeit a very thin layer, and this is securely bonded to the underlying metal. The other point is that the item should be cleaned thoroughly afterwards as there will be traces of ferrous sulphate which could be corrosive.
While not having used this method myself I have, when I was a kid, dipped ferrous objects into copper sulphate solution to copper plate them.
Cheers
Martin