Odd browning problem

[Robert Wolfe]

I can't for the life of me get a cock screw to brown despite the fact that everything else on my rifle has browned just fine. I've cleaned it multiple times, used Tracks Tried and True brown, Laurel Mountain brown, even vinegar and salt in desperation but all I get is gray. No rust at all. I do my small parts in a plastic sweater box with a heating pad underneath. Wet paper towels inside for plenty of humidity. Dampen with new solution every 3-4 hours in the day, no carding, two weeks - this should be a shaggy, rusty mess. Is this just a strange alloy that is resisting rust? It is a standard lock part, not something I made. Give up or try something different?  Two pics for visuals. First is after several days with Laurel Mountain (after trying Tried and True and then vinegar looked similar). I think the brown is simply dried solution. Second pic is after scrubbing with soap and water and a paper towel. If you zoom in on the second pic you can see file marks untouched by the solution. 

[J. Talbert]

Sure sounds like you somehow got a screw from some other alloy than is typical.  I’d ask the manufacturer for a replacement . 
Jeff

[rich pierce]

Chambers top screws are hard. Chuck it in the drill or drill press and sand it to 240 or 360 grit at most to give more surface area for the solution to bite onto. Happens with frizzens too more often than not.

[Ian Pratt]

I hate when that happens.

I assume we can rule out some kind of oil or grease contamination so it is likely the steel. If you sand off a spot and swipe with cold blue what does it do?  I remember having trouble with stubborn alloys before and was able to get parts to rust better after heating, might give that a try.

Over a span of maybe two years I had three locks from the same maker that came with stainless tumbler screws. Stuff happens.

[Robert Wolfe]

Ian - cold blue does nothing.....

[Not English]

Robert, check to see if it's magnetic. If it's not, chances are real good that it's some non-ferric alloy and probably won't brown.

[Robert Wolfe]

Magnet sticks. I think it was made from some rust resistant alloy by mistake.

[Daryl]

Highly unlikely due to its origin.

[Ian Pratt]

Ian - cold blue does nothing.....

Then I'd say it's either some type of stainless or there's some super evil barrier on it preventing rust. If cleaning with lacquer thinner, heating it to a dull red and then sanding it clean again don't change anything, time to make a or buy a new screw

[Robert Wolfe]

Thanks all - time to abandon ship.

[Berksrifle]

 It's a good chance it is 17-4 PH. This is a medical grade stainless steel used for medical tools. It can be heat treated but it will not rust.

Ken

[Ian Pratt]

 KRYPTONITE ! RUN ROBERT!

[RJD-VT]

It's a good chance it is 17-4 PH. This is a medical grade stainless steel used for medical tools. It can be heat treated but it will not rust.

Ken

I agree with Berksrifle. 17-4 has a fair amount of chromium in it which makes it mildly resistant to corrosion (like your 2nd pic) until it is passivated. Then it becomes very resistant to rust like any other SS.
Having magnetic properties, it’s easy to mix up at the mill or shop. I have seen that mixup quite a bit where I used to work.

~Bob D.

[Scota4570]

I never brown screws.  Polish it,  then heat it to just a faintest red glow , about 900* F, then dunk it immediately  in canola oil.   It will come out blue black, normally.   

[alacran]

I do as Scota4570 says. However I case harden lock bolts, especially on a flintlock, since they come off for cleaning, after shooting it. The casehardened screws do not take bluing well at all, and it wears off rather fast. I have used Super blue, Perma Blue, as well as Ospho blue. They all wear off.

[Dutch Blacky]

There is an old technique of blacksmiths in german called "schwarzbrennen". I do not know the english technical expression, and a crude translation might be "burnig black". Iron is heated in charcoal (to 400° - 600°C) with linseed oil and gets a black surface. Maybe this might work with your screws?

[smart dog]

Hi,
Did you check to see if it was hardened?  Can you file the notch or does a file just skip over it?  Also, forget browning it, just polish it bright and then heat it until it turns deep blue. 

dave

[Robert Wolfe]

Not hardened - filed just fine.