Of course they are, but they can be controlled, to some degree, by the mixtures of the packing, (types of charcoal used, and the amounts of each), temps, distance from the "dump" to the quench, oxygen content of the water, and other things. If it were as simple hardening the metal then all would look the same.
I bought an old friends' heat treating oven, and all his supplies for case hardening last week. I will be making a foray into the "black art" sometime in the future, with a few old junked receivers.
Thanks, Stan