ALL the modern CBs I know have fiberglass or carbon limbs. However, all "serious" machinary relies on STEEL for springs. including "leaf" (flat) springs.

As far as I know, steel is also used where weight matters, like in aviation. So I guess it has better weight to strength ratio.

What is wrong with steel for bows?

(I consider building steel CB, so I need your input before I waste my time and money).