Hi,
Nick you answered your own question about case hardening with motor oil. Let me clarify this case hardening stuff so you all are on the same page. Wick, please correct me if I get anything wrong. In the old days before 1850 or so, steel was an expensive commodity because it was expensive and slow to make in any large quantity. You had blister and crucible steel and that was it. In fact, during the 17th and early 18th centuries, steel was as valuable as silver. In 1700, gun makers mounted their high-end guns in steel, not silver. So lock makers reserved their steel for springs, frizzens, and frizzen soles. All of the other parts in the lock were made from wrought iron with little or no carbon so it could not be hardened. To get around that, the wrought iron tumblers, sears bridles, lock plates, flintcocks, and top jaws were case hardened. So the wrought iron parts were packed in an iron box filled with a source of carbon like burnt leather, bone, or wood charcoal, and heated to some temp above 1375 degrees. It was soaked at that heat so the surface of the iron could absorb carbon and become steel. The longer the soak, the deeper the skin of steel. Then, the contents of the box were dumped into room temperature water, which caused the steel on the surfaces of the parts to harden. Because the interior of the parts was wrought iron, it could not harden, so the part was like an egg, hard on the outside, soft in the middle. Consequently, it did not require tempering to make less brittle.
Fast forward to today. Most of our lock parts are cast from some steel alloy and most will harden without casing and they will harden all the way through. They contain enough carbon to harden when brought to a high temp and then quenched in water, oil, brine, or whatever. So, when you case harden modern lock parts, the interior of the part is not soft and requires tempering to reduce brittleness, unlike the old parts from wrought iron. Most modern parts do not require casing. They can be successfully hardened just by heating them red hot and quenching. However, during that process, carbon may be burned off the surface of the steel. That is why, modern steel frizzens often spark better when case hardened than when just heated and quenched because the casing process adds carbon lost during heating. Moreover the case hardening process will add carbon to the surfaces of parts made from 5160 and 4140 steel commonly used for cast lock parts today, giving the surface a higher carbon content. That gives them a stronger surface to resist wear. But they must be tempered before use unlike the old wrought iron parts. The depth and degree of carbon added during case hardening depends on temperature and time at that temperature. No case hardening from coating with a compound like Kasenit, heating for a few minutes and then quenching will be very deep, and any case hardening resulting from the few seconds of quenching in motor oil can possibly be deep. We measure time for casing in hours, not seconds.
dave
dave
