It's not worth your time to try to fix a crack, because short of cutting it off and forge welding on a new tang, or cutting it up, stacking it, and forge welding it together into a billet, there isn't a way to fix it that isn't prone to failure. It will be easier and quicker to just throw it in the box of broken projects that everyone has in the corner of the shop, and forge a new one and make sure not to hammer below a red heat so that it does not harden and crack again Or, if you were using scrap steel like leaf springs, it might have had a pre existing crack. Also it is my opinion that If you have one crack, there is probably another hiding somewhere in the steel that you can't see yet.