What is involved in heat treating a knife blade? First and foremost there must be enough carbon content in the steel to harden it....in the region of 1 to 2 %....too little carbon there will not be enough carbide crystals formed to give the edge wear resistance. Too much and we end up with a brittle blade that cannot be tempered enough to remove that brittleness. Think cast iron which can be broken with a hammer even in thick sections. Secondly the steel must be heated above a critical temperature unique to that particular steel to release the crystal structure already in the metal and allow the free carbon to form carbon centered crystals called carbides. The more carbides the more wear resistant the blade will be. Thirdly after heat treating the blade will usually be very hard and brittle so it must be tempered to remove that brittleness by heating to a medium temperature, usually 300 to 500 degrees F. These are basic rules only there are exceptions based on the chemistry of the particular metal used and the desired use. The purpose of heat treating is to create a wear resistant blade with sufficient flex to resist breakage. I am leaving this thread open to allow as many people who have questions to ask them. Please feel free to contribute.