Maximum attainable hardness levels out around 60 or 65 points. The more carbon available, the more martensite which can be formed. The maximum attainable hardness of a given piece of steel versus the carbon content forms a curve on the graph. There is no magic number above which steel will harden or below which it will not. No disrespect meant to a fellow electrician, but I'm going to get nitpicky here. No you cant HT a spike, sorry read about heat treating and you will understand that one needs at least 35 points of carbon to harden a steel
