When heated to 90%+ transition, certain ferrous alloys will develop a bluish tinge as the temper is drawn and the metal becomes too soft and weak to absorb the shock of firing live ammunition. Worse, exposing annealed ferrous metal to carbon will render the metal "case hardened" and is not only very weak but brittle in addition.
I suggest that you practice the usual passivation, oxidation, and alkylation, that occurs in a normal ballistic metal bluing process. Failing that, consider the less expensive "Parkerizing" technique.
a.I'm trying to learn the original process done by Colt in the percussion revolver era. The parts supossedly were put on hot coals and periodically wiped with rags containing lime or fish oil. The charcoalbluing process is done on firearms,including modern, by gunsmiths around the country. Turnbull Restorations being the best known. Charcoal bluing was done in the most early years of the Colt factory starting in 1836/7 and until the percussion era was over and the more modern 1873 Single action Army revolver was born. The carbonia Bluing was started aboutn that time.
Casehardening is where metal in a closed crucible is heated to critical temp and held there while wood and bone charcoal in with the metal gives off carbon that is absorbed into the surface a few .001's inch and......then the metal is dumped from the crucible into a quench bath of water and is thus hardened. The hardened metal is then later tempered at a much lower heat to remove the brittle and leaves a surface of hard carbon with an interior of tough but malleable tool type steel.