Every now and then I come across a screw on a used gun that has the head buggered up so I usually just clean it up with a file or maybe a Dremel tool, but then it needs to be re-blued. I'm not sure where I heard about this, but I use a propane torch to heat the screw and then plunge it into used motor oil. The screw will come out with a deep blue, almost black and it seems to last as good as any. Much better than any cold bluing I've tried. I'm not sure why it even works, maybe someone out there with a chemistry background could explain it, but I thought I'd pass it on to all of you.
Don

I'm gonna have to try that . I have never heard of that method thanks for the tip Don .
Joe

You aren't the only one that is going to try it Joe.

BigBlue, a big thanks if this works for me.

Eric

Got to try this, but I am also worried if the screw would then be brittle due to the heat hardening.
If the screw snap in the woodwork during shooting or assembly then it would be a great problem to remove.
Maybe there is a way to draw it back..

I have some experience in heat treating and will give you my two cent's worth.

All screws and bolt have a rating, That rating is based on the heat treatment applied, and subsequent annealing and additions of cyanide, or other chemicals to make the item either case hardened or through hardened.

I do not know what the specification is for a screw or bolt used in assembling a firearm is, but I can assure you there is one, and that it is important!!!!!

Since, normal steel will get harder using the technique you described, it will also become more brittle. Without substantial testing it would be impossible to determine what effected that embrittlement would have on any particular piece of metal.

Here is an excerpt and address form a website that describes what heat treating does. asuwlink.uwyo.edu/~metal/heat.html

Quote::

Heat Treating (annealing/hardening/tempering) Metals Heat treating is a *huge* subject, and depends on the metal, and intended use. Most of the time, this question is asked regarding steel, so we'll give a brief description of that, based on an article in Home Shop Machinist (Sept/Oct 1991, "Heat Treating Basics" by Steve Acker). Iron will, at common temperatures, organize itself into an atomic structure that is called "body centered cubic." This consists of overlapping cubes with an atom at each corner, and one more in the center of the cube. But above roughly 1400 degrees F there is a change in structure to "face centered cubic" and the central atoms migrate to the faces of the cubes. This latter form is not magnetic. Steel is basically iron with some carbon mixed in, though modern alloys have various other metals and substances as well. When steel is heated to the critical temperature (about 1400 degrees F), the iron will change to face centered, and the carbon atoms will migrate into the central position formerly occupied by an iron atom. This form of red-hot steel is called austentite. Since it is not magnetic, a magnet may be used to determine when the critical temperature has been reached (though the magnetism may be lost before the transition, so this is only approximate). Complete migration of the carbon atoms may take a minute or two. If you let this cool slowly, the iron atoms migrate back into the cube and force the carbon back out, resulting in soft steel called pearlite. If the sample was formerly hard, this softening process is called annealing. If you cool (quench) the sample suddenly by immersing it in oil or water, the carbon atoms are trapped, and the result is a very hard, brittle steel. Too brittle for most uses. The structure is now a body centered tetragonal form called martensite. So, the next step is to heat it back up, to between 200 and 800 degrees F or so, depending on the desired end hardness. This allows some of the hardness to relieved and is called tempering. The amount of tempering that is desirable depends on the final use. Cutting tools are very hard, knife blades less so because they must flex under use rather than break. Tempering is a trade-off between hardness and flexibility. Accurately measuring the tempering temperature is important. A nice, expensive thermostatically-controlled oven is great. Or, some special compounds can be applied that melt or change color at the right temp, such as Tempilstik and Tempilaq. If the steel is clean to start with, then you may notice that it goes through certain color changes as it heats up, with understandably vague descriptions such as "light straw" indicating about 440 degrees F, and purple=520. These colors are not incandescence colors, but are viewed in normal room light. The colors are due to types of surface oxidation that are temperature dependent. When quenching, it is often very important to avoid stirring a part because this will cool one side much more quickly than the other, and might cause warping. For knife blades, as an example, move it strictly up and down during the quench.

Embrittlement of screws and bolts is a big issue in indutry.

I am only waving this red flag because I would hate to hear of anyone doing this winding up with a the head of a screw in their eye socket.r their cheek blown off.

Sorry to be a wet blanket, but safety first.

Lester,
Good points for sure. Safety should be of the first consideration and I'm not sure that I've ever used it on anything where pressures were a critical factor. I remember using it on grip screws, on lever actions foregrip cap screws and tube magazine screws and had never incurred a problem with those applications.
Don

The hot bluing of steel can be done without hardening the metal signifigantly. I doubt that a propane torch will get a screw to the "critical" temperature that is required to harden the screw.
The color change that takes place is due to oxidation of the surface steel in combination with the oil that not only halts the process but adds an oxidation layer to the steel. You can do the same thing with a red hot piece of steel and lay the screw on it until it turns the blue color you want and then quench in oil. It is a standard heat treatment to reduce the brittlness of hardened metal.
The way to tell if you are reaching the "critical temperature is to hold the screw with a magnet - if it loses its megnetic properties then you have reached the critical temperature and you are hardening the screw. If it stays stuck to the magnet throughout the process there is no dager of hardening.
I use this method when making springs all the time.

I've been doing this for years Big Blue.

I started experimenting with trying to get some sort of case hardening effect on steel...to no avail. What I did discover though is, if you gently heat the part to the point where it turns blue then quench it in the used motor oil, then it takes on a beautiful deep blue/black colour.

When I say...it turns blue...it you heat a piece of steel, watch the colours it goes through as the heat builds. It turns blue way before it gets red hot, so I cannot see that there is going to be any appreciable change to the hardness. Sure there will be minor changes, but from my experience, very little.

I must point out though...this method is only useful on small parts. The biggest part I have used it on was a rear sight, the same size as that found on the Winchester Model 94. If you were to try it on larger parts you would not be able to get a uniform heat or a uniform blue colour all over, and then, you would no doubt affect the hardness detrimentally.

But, it does work, and it does look damn fine.

Cheers, Vince

At what temperatuure does the steel turn blue? I'm wondering if to could be heated evenly in an oven. A friend has a small kiln that might work for larger parts.

Pumpkinslinger,

I would advise against that as it will be applied to the entire object. If the guys are just applying a flame to the head at least it will not likely affect the temper on the threads.
I do not think though that you need to heat the head till it glows red to achieve the blackening effect.

I am probably being over cautious, but I've seen the effect of a bolt overstressed to the point of failure. The supplier did not supply the bolt as specified for an Ingersoll-Rand compressor. It killed the technician that was trouble shooting the machine.

Yeah, Vince I hear ya. I am only trying to say that caution should be exercised by not heating the item too much. I do not believe that it needs to be red hot to get the effect desired.

I really don't mean to be such a pain in the a--.

Les, thanks, but I'm thinking more along the lines of bluing replacement sights, etc., not "structural" parts.

Just remember when you dumb something into oil when the item is hot, it has to go ALL the way into the oil, do not keep anything that was heated near or at the surface of the oil.

Otherwise you may start a oil fire. Even when something is red hot, if you put it in all the way the oil cannot get oxygen to combust. But above on the surface and it will light.

Dimitri

A propane torch will definately change the temper of a screw. I have heated screws to RED hot with a propane torch with no problem. I do not think this is a good idea...

Hey guys....the head of a screw, or sights NOT attached to the barrel, will turn blue way before they get red hot.

I suggest that you do as I did...a little experimenting. Get a small piece of steel...similar in size to the largest part you are wanting to "blue" and hit it with the heat and watch the metal carefully for changes in colour. Obviously, the hotter the flame, the quicker the changes...to the point that you may well miss the colour change, so go slowly...or as they say...slowly slowly, catchey monkey.

You can also experiment with "colouring" just one part of a piece of metal until you are satisfied that you can do it without affecting any screw threads.

'Mitri brings up a good point, although I don't believe that the metal gets hot enough to ignite oil from memory. I only used a very small container for the oil...enough to cover the part entirely plus a little more to aid in cooling. However, BE CAREFUL.

Cheers, Vince

Lester....you ain't being a pain in the butt mate...you are simply advising caution...and with good reason.

The sort of small items we are talking about here are not usually load bearing items.

I agree with your advice of CAUTION regarding large items or load bearing parts...this is not the process for them.

This process is simply for a cosmetic effect on small items.

Cheers, Vince