It depends on a couple of things. 1. Was the saw blade a bi-metal blade with just the edge hardened or made from a heat treatable steel ? 2. If it was a steel containing enough carbon to harden was it overheated during the grinding process and now requires heat treating? Just because it was a saw blade does not mean that the material used was a heat treatable steel suitable for knife construction. Take a small piece of some scrap material ,heat it red hot until it is non magnetic and quench in oil, test the hardness with a file, this should give you some indication if the steel can be hardened.
