There are some full scale motorcycle engine rings made of spring steel like the old Slinky toy and about as thin. The theory being that it reduced ring flutter at 18,000 R.P.M. Most if not all piston rings I have used were cast iron but I have no knowledge of metalurgy. I do know that cast iron is very hard and should exibit good wear characteristics. Hence cast iron pistons in Enya engines. I also think cast iron has a very low expansion rate making it a very stable material.

Bill