Bluing low-grade SS parts

[Tokarev]

When I am not in a hurry having the parts blued, I usually dump them into a bottle of cola that contains H3PO4 for a couple weeks. This works fine for carbon steel and produces flat black gloss bluing.

But the same method used on low-grade SS produces light-gray matte bluing with crystals of rust popping up like small pox. So can't use that.

Tried parkerizing, but the part instantly turns rusty the moment park solution dries up.

I ended up just putting the parts over electric burner and heating under a stainless dog bowl for an hour at about 550-570F. They now have nice deep blue finish.

What can you suggest for an alternative bluing of low-grade SS? This is mostly for cosmetics, as it would not really rust - just turn brown and stay that way.

[375RUGER]

That blue color is not very tenacious and can be wire brushed off. I don't really know of a way to "set" it.
What you have done is change the corrosion resistance of the SS becasue you have altered the chromium rich oxide film that protects the SS underneath. This oxide film is what makes SS stainless.
You may see no reaction if the service conditions of the "blued" parts are not subject to conditions that would cause rust. True if you have indeed maintained a temperature measured on the part to be less than 800*F.

[sbowers]

Why not just get the proper SS bluing salts from brownells. If it is worth doing it is worth doing right.
Steve

[220swiftfn]

It sounds like what you're doing is temper bluing (same as niter bluing, and as stated, not very wear resistant.) What you were doing with the carbon steel and Coke is called "pickeling" and it does help the blue take better, you can do the same with stainless. Usually the etchant is nitric acid (doesn't work on stainless), but you can make a weak "aqua regia" that should work with nitric (3-5%) and hydrochloric (1%). Other than that, jeweler's etchant (Spencer's acid) is what is recommended, and then slow rust blue will take on the stainless.....

*NOTE*
This is from Angier's "Firearm Blueing and Browning" from the '30's, but should still be valid.


Dan