simple and effective, works for guns as well...
its thumb tight in a 2 pound locomotive do you really think hardness is an issue here ?you do realize that quenching in oil after heating it to that point does make it harder, and more brittle ?? shold give about brinell 55 where as water would give approximately brinell 60 ..
i am a 01 and 03 F.F.L. holder, i was a small arms repair instructor at Aberdeen proving grounds. this method is safe to use in ANY firearm. not a whole lot of stress on a side plate screw in a revolver or the grip screw in a 1911. there are not a lot of screws in ANY modern firearm. in the last 5 years i have broken ZERO of these black screws.in a two pound loco, nope ...
but in a gun, yup ...
depends on end use, your's is okay ..
Obviously, it works for this guy as well.My favorite way to blacken steel, iron or even zinc-plated hardware is to brush on a thin coat of liquid “gun blue” – typically a combination of selenious acid, nitric acid and cupric sulfate. If you brush on a thin coat it will blacken a ferrous metal almost instantly, including zinc-plated hardware.