Hi,
I usually case harden lock plates, frizzens, and flint cocks. It is not really necessary to harden the flint cocks or plate, however, I've repaired quite a few lock plates on which the shoulders where the cock hits was getting peened down and damaged. When locks were made from mostly wrought iron, case hardening those parts was important but that is not really so anymore. I do it mainly because it prevents any damage to the lock plate and helps resist corrosion since most of my locks are simply polished and not browned. I almost always case harden the frizzens because I usually have to anneal them so I can engrave them. I also believe it enhances the sparking of any frizzen, however, after reading Jim Chambers' post about steel alloys used in locks, I am not so sure I will case Chambers frizzens anymore unless I anneal them. He described their process for carbonizing the surface after casting and that should eliminate any benefit from additionally case hardening them.
Anyway, getting back to to Monro1066's original question, I case harden using a heat treating oven. I pack the parts in 50% bone and 50% wood charcoal within a steel box with lid. I heat that usually between 1475-1575 degrees depending on my objectives, let heat soak for 90-120 minutes and then quench in 6-7 gallons of room temperature water. I choose the higher temperature if I am just hardening the parts and will polish them bright and the lower temperature if I am trying to achieve colors. After quenching I temper frizzens at 375-400 degrees for 1 hour and let cool slowly. Then I use a mini torch and heat just the toe of the frizzen until it turns dark blue. For all the other parts, I temper to 590-600 degrees for an hour and let air cool. Be forewarned that if you case harden the lock plate, it may warp when quenched so thin plates should be blocked by attaching them to heavier steel plate. I place the plates on edge in the pack so the edge hits the water quench first rather than the flat surfaces of the plate.
dave
