I make most of my knives out of some old saw blades from a mill that shut down long ago, they are the old ones that were high carbon steel through and through and not just in a ring around the edge like the newer ones are. I have a bunch of these old blades saved up.
I can get a hardness of 57-58 on them pretty easily, and I usually anneal the spine of the knife for increased durability.
If I want to make something thicker (like a Kukri, or machette) I will start with a leaf spring, they make a pretty good blade.
I think I am going to look into these axe heads, and see if I might be interested in trying my hand at making one.