Removing steel , leaving brass

[SpionKopKid]

I recently found a piece of an artillery shell in Gemmano (Italy).

The shell appears to be a brass/steel hybrid (I can't see any markings on it yet), the steel has effectively disappeared apart from rusty bits stuck to the brass. I was hoping to use it as a nice paper weight and want to remove all the steel completely. Has anybody got any suggestions to do this? any chemical combos that will target the rust/steel and leave the brass untouched?
Thanks for any help
Rich

[woody50]

Well steel or iron will rust, just like you say. And brass does not. So the trick should be to make the steel/iron rust faster, leaving the brass. Water? Salt water..... Don't really know, you need a plusrust instead of an antirust....