I have no doubt that the gun mfrs were playing with steel alloys in the first half of the century and earlier. I think they're still tinkering around with alloys.

As to whether or not "chromox" had carbon of sufficient quantity to harden, I suspect it did. I also suspect the "chromox" barrel steel wasn't used for frames. I welded LC Smith barrels from the 20's era and found that they hardened at the weld HAZ and weld bead from the 'self-quench' even though I used a mild steel rod.