Absolutely. I've forged old springs, bush hog blades, etc into blades and it's good practice, but when I first started out, I was advised to buy some good flat stock known-type steel to learn on and I think that was good advice. You can always branch out and play with scrap tool steel later.
I've got a bunch of 52100 steel in 1 1/8" round bars and I've forged a couple of blades out of that stuff with a hammer and anvil and it was WAY more work than I antcipated. That stuff doesn't move under the hammer nearly as well as 5160, O1, 1084 etc. I finally got my brother the millwright/welder to make me a little rolling mill and now it's quick and easy to roll that stuff into flat bar stock about 1/4" thick. Once it gets that thin, it takes much less time in the forge each time to get it up to forging heat and it moves a lot easier under hammer than the thick rods too.