Tungsten carbide is one of the hardest metals. However the sharpest edge blades are made from high carbon steel. The leaf springs from trucks are an excellent source of High carbon spring steel. That is why the Gurkha Kukri has been made for decades from the leaf springs from Mercedes trucks. High carbon steel will hold a very good edge but is prone to rust so a light coating of oil is always needed on the blade. If you can't get hold of a leaf spring, and old file would also make a good blade, it would have to be annealed to work on then tempered to the right level to take the edge. The only more sophisticated blades are that of traditional Samurai swords, the level of workmanship to make such a fantastic blade is only in the realm of the master Japanese sword smiths and metal polishers. It is simple one of the deadliest blades ever made.