"How It's Made" Episode on the Uberti Cattleman

[Driftwood Johnson]

I agree with denster, you can get very nice case hardening and coloring by what the British call "cyanide mottling." Probably the outstanding American example is the Stevens 44 1/2 with its ripple of colors from the way it was quenched.
Just because Colt used the older and slower pack hardening does not make others else wrong for using a different process.

So my question remains. Does this method infuse extra carbon into the surface of the steel or iron? If extra carbon is not infused into the surface, it is not 'case hardening' in the literal sense of the term. As I'm sure you know, Case Hardening means the outer surface, or 'case' of the metal has been hardened by infusing more carbon into the surface than exists in the alloy to start with. The colors of Case Hardening are just a byproduct of the process, they are not the reason the surface of the metal was hardened.

 

[Jim Watson]

Cyanide treatment is a process adding carbon to the surface of the steel. Yes, it is case HARDENING else the old timers trying to speed up the process from laborious pack hardening would not have fooled with it.
Wiki says:
Cyaniding is a case-hardening process that is fast and efficient; it is mainly used on low-carbon steels. The part is heated to 871-954 °C (1600-1750 °F) in a bath of sodium cyanide and then is quenched and rinsed, in water or oil, to remove any residual cyanide.
2NaCN + O2 → 2NaCNO 2NaCNO + O2 → Na2CO3 +CO + N22CO → CO2 + C
This process produces a thin, hard shell (between 0.25 - 0.75 mm, 0.01 and 0.03 inches) that is harder than the one produced by carburizing, and can be completed in 20 to 30 minutes compared to several hours so the parts have less opportunity to become distorted. It is typically used on small parts such as bolts, nuts, screws and small gears. The major drawback of cyaniding is that cyanide salts are poisonous.

 

[Driftwood Johnson]

Thanks for the clarification.