Isn't the reason for case hardening to add enough carbon to a steel for it to have the ability to harden. I believe it takes quite a while for carbon to diffuse, so it may be difficult to turn a low carbon receiver into a high carbon steel that could actually through harden. Doesn't the hard layer end up only being a few thousandths thick.
I believe color casing might be different. I've been curious to know if the steel case on a part actually hardens if it's not quenched from a temperature that's somewhere around nonmagnetic. I've wondered if a wear point is actually hardened if a part is quenched from say 1200*.
