Hi ya'll.
I'm new here, but saw the post and thought I'd chime in. Blackbeard, you got yourself a sure-nuff piece of knifemaking steel! Leaf spring is usually really good steel. Most leaf springs are made from 5160, which is an excellent blade steel. 5160 is my primary blade steel for just that reason. If you can get a coil spring, and straighten it out, that's usually good steel too. You want to heat a small piece of your steel to orange-hot, quench it in oil (transmission fluid or vegetable oil will work) that's heated to about 90 degrees (you can heat the oil by dropping a heated piece of steel in it before you quench the test piece). Once the test piece is cooled, run a file across it - it will probably slide like it's on glass, which is what you want. If steel gets that hard and resists a file like that, then it's probably good for making knives. Otherwise, if it was me, I'd forge it down to shape using a hammer and an anvil-like object (I say that because a 100# piece of granite will work for an anvil...). If you're going to grind it, or use files to shape it, anneal it first. 5160 is super tough stuff, and is not easy to grind or file. Anneal by heating to orange, and burying in about 2 feet of vermiculite, wood ash or ashes from a bbq grill (make sure there's no charcoal in there or it'll ignite!), or even burying in about 2ft. of dirt. Leave it for at least 6 hrs, if not longer. The longer and slower the steel cools, the easier it is to grind or file on. If it cools too fast, it'll harden up and Hercules wouldn't be able to shape it. If you're really interested in learning how to make knives, get a copy of Wayne Goddard's $50 knife shop. I've been forging for about 6 years and I still use that book as an information source. Any questions, please feel free to email me. Happy knifemaking, dude!:D