If you come across it again, you can put the tip on an anvil, put on your safety glasses, and give it a good, hard whack with a hammer. If it's hardened steel it will break. If it's case hardened, it won't. Or you could harden the tang and try to break it. Either way, all you'll know is if it's a hardened steel or just case hardened. Most of the older American made Nicholsen's were 1095 (at least the one's made in north Alabama). I found a Brazilian made Nicholsen rasp that was case hardened.