After a shape is made on a knife, it needs to be heat treated. this involves heating the knife to around 1500 degrees in a furnace or forge until the metal changes its chemical formula. In my case, the machine shop is blessed to have an industrial toaster/ heat treating oven for this specific process.  It becomes incredibly hard, so tough that no other tools could dent it. After heat treatment, the blade is quenched in an oil bath to cool it down. After this process, the blade is brittle, making it susceptible to shattering. The next step is thus softening the blade to take impacts without cracking like glass. To accomplish this task, I have my household toaster to hold the blade at 375 degrees Fahrenheit for an hour.