Hi LRB and Bob Roller,
Thanks for the posts. I stand corrected. TRS frizzens with 6150 being a medium carbon steel should definitely be case-hardened or soled. I never notice a problem because I pack harden all of my TRS locks for 2 hours in a mix of bone and wood charcoal with a water quench. They all spark fabulously even after much use. However, I always thought they could be hardened through just by heating without having to resort to adding carbon. Even if they could be through hardened, I prefer pack hardening because there is something almost oily smooth about the surface after pack hardening that doesn't occur with through hardening.
dave