I posted some pictures in the thread below, making a pair of flat springs.

http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=349007#Post349007

There are dozens of steels out there that could be called "spring steel". I would use a known alloy, and then you have the exact heat treatment specifications. Hardening and tempering can then be done in a furnace with predictable results. I make springs on an almost weekly basis, and I don't want to do them over, so I must use a known process.