Jim
I know you know more about metallurgy than I, so this is an honest question: What drove the selection of 1018 with case-hardening versus an alloy or "high-carbon" steel?
Aside from that curiosity, it looks like a real lock for the period, and I'm sure it will work like a champ. Seen several of your kits now finished by locals, and the quality of the kits is obvious!
Good question. Given the requirements of the parts and considering what was done originally it becomes clear that any number of different alloys would work fine for the tumbler and sear. I guess I chose 1018 for a few reasons, but might have been as well off with another choice. Here are some of the benefits of carburized 1018:
The material is readily available in a variety of sizes. This is important when setting up for CNC work
The material is cheap
It machines reasonably well
Heat treatment by pack carburizing allows a large number of parts to be heat treated at once in our shop.
The hard case and softer interior works well for parts such as these.
A free machining variety of mild steel might be something I consider in the future. Speed and process reliability become important with processes such as these.
Jim