The main difference between ferrous and non-ferrous metal is that the latter doesn't contain iron.
Typically speaking, ferrous metals have a high carbon content and rust easily when exposed to natural elements. Obviously, frag feed and cast iron are ferrous metals, however other metals like steel turnings can also be classed as ferrous.
Non-ferrous metals have a higher resistance to rust and can be used in most outdoor objects because of this. Metals such as copper, aluminium and brass are classed as non-ferrous.