Let me be explicit, case hardening and heat treating are two fundamentally different processes.
....the other reiles on the diffusion of carbon into the surface of a material to increase the surface hardness....
I believe if you case harden, harden being important, you had to do the exact same fundamental metallurgical process. Carbon alone in iron will not harden unless its arranged as martensite. I don't believe its possible to 'case harden' and 'heat treat' as two separate procedures on the same low carbon receiver using charcoal pack and water quench.
I suppose heat treatment is generally thought of as hardening, but I guess steel might be treated with heat for results other than hardening. I'm still not sure though what process or goal of 'heat treating' the core of a low carbon steel receiver would be.
