Re: Making firing pins
Steel can only be heat treated if it has some carbon in it. What is being done in heat treating is freezing the crystalline structure in one of several possible configurations. The structure that you get from heating it to red hot and cooling it rapidly is a harder structure then if the cooling is done very slowly (called annealing) and the crystalline structure is allowed to take its low temperature configuration. Its all about how the carbon molecules are placed in the crystalline structure.
When we force cool red hot steel, we freeze its crystalline structure. To get to somewhere between full hard and full soft, we heat the full hard steel to an exact intermediate temperature and hold it for some exact period of time to allow the carbon atoms to partially rearrange themselves leaving less of the steel in its full hard state. That is called drawing the steel. You are drawing the hardness to some lower level of hardness. It is a science to get it just right.
But according to AGI that is not the process to use for a firing pin. They say use mild steel (which CAN NOT take a heat treat), case harden it (allow carbon atoms to migrate into the surface layer of the mild steel making a hard case around the tough mild steel interior). Kasenit is a powder (probably pure carbon) that you put all over the surface of the part when it is red hot so it will infuse into the surface. That surface is then hard from the carbon and since mild steel will not harden with heat alone, the inside is still soft and tough. The "case" is only a few thousands of an inch thick but makes the part's surface more wear resistant and less like to peen over in the firing pin case.