Heat treat scale prevention

[oldred]

I need to heat treat some small O1 parts and since at least one of these needs to retain it's smooth surface I would like to get some ideas on how to do this without the scaling normally encountered when heating parts to the required temperatures? I am already familiar with the commercial anti-scaling compounds and stainless wraps but I don't have either on hand and I need to do this today. If what I am asking is impractical I will just order some compound from Brownells and wait but if anyone has a neat trick or two they could share I would greatly appreciate it!


On another forum a couple of years ago it was suggested to use a brazing (or soldering?) flux but of the two types I have neither works very well, of course it may be my error and not the flux to blame. Try as I might I could not find that thread over there but then it occurred to me that if anyone knows how to do this for gun parts it would be a gunsmith of which I have discovered there are several very talented ones right here!

[andrew375]

I've seen covering the surface of the part in pencil lead, 2B or 3B should work. A way I've used is to dip the part in oil (not engine oil as it contains, amongst other things, anti-ashing agents) and then gently burn the oil off with a blow torch. Do this a couple of time and put the part in the oven with oil coating it. The idea is that the oil oxidises, forming a sacrificial coating if you will. Done right I get a nice even black finish. If you want the part "in the white" you will have to polish off the surface, but there wont be any pitting or scaling.

[oneokie]

If the parts are small enough to fit in a pipe nipple, place the parts and some paper or other combustable substance in the nipple and put caps on the ends of the nipple and heat the whole thing to the desired temp and hold it there for the required lenght of time. Then drop the whole thing in a container of salt water, and agitate.

Another method is to make a paste of brazing flux, coat the object with the paste, let it dry, and then use indirect heat. I use a piece of thin flat metal held in a vice to hold the part, and use a cutting torch underneath the flat metal.

[bangerjim]

You need to keep the O2 away from it. The above coatings may work. I've never used them. I have a full vacuum heat treat furnace I use for tools and parts. Goes to 2500F.

The nipple thing above is the closes you will get, as the paper inside consumes the O2. Or you could fill the nipple with N2 to force out the air. You would have to make little connections on the ends for filling and evacuation and then isolate from the atmosphere. Not out of the question, but I do not know your skill level or what machine tools you have at your disposal.

Foil wrap may be the best way if this is just a one-time thing.

Good luck.

bangerjim

[oldred]

The pipe trick sounds like it would work and while I do have inert gas handy (C25) the paper sounds as if it might be easier. I suppose that maybe I could thread a cap on one end of the pipe then have a slip fit (loose) cap on the other so I could heat with my Oxy/Acetylene torch then dump the contents into the oil quench by up-ending the pipe close to the oil surface??? Does that sound about right?

It won't be a major disaster if I do get some scaling but I did want to keep these parts as blemish free as practical, I need to run out to Lowes for another errand anyway so I think I will do that now and get myself some pipe and fittings while there then wait until morning to tackle these parts.


Thanks, I hadn't thought about sealing it in a small container like that.

[leftiye]

For hardening, Brownell's sells Keepbrite in cans. Dip part in it, heat red hot, quench in appropriate medium. Tempering can be done in borax bath at correct temperature. Or by color. If you're going to put metal in pipe nipple, you might want to look at case hardening while you're at it.

BTW, those borax baths will go high enough to harden steels too. Put metal in container and cover with mashed or powdered borax, then heat. You'll need tongs or some other way (wire hook on part) to remove from bath and dump into quench.

[Zymurgy50]

Silver solder flux. Heat the small part to about 250-300* and cover the part in the flux. The flux will melt and form a protective coating. After heat treatment clean it off with soapy water and a toothbrush.

[oldred]

Ok I used the pipe but also used the burned oil coating that was suggested since the heating would be indirect, I then (using tongs and while still hot of course) held the pipe nipple over the oil right at the surface so that I could dump the parts out of the pipe without exposing them to the air any more than the 1" or so drop and they turned out perfect. I tempered at 400 deg in an oven while the coating was still on them then took them out to the shop and polished them, they are hard as $4 worth of jawbreakers and without a trace of scaling!

Zymurgy50, I didn't have any Silver solder flux on hand but I will certainly keep that in mind since I will be doing this again, Thanks to everyone for the suggestions.

BTW, these parts are for my scratch built scaled down "Baby" high wall project that will be finished in a few days, I hope to get some pics up when I get the bluing done.

[DeanWinchester]

In the T&D shop I worked in we used a stainless wrap, like reynolds wrap on steroids. The pipe should work well enough. Be sure and toss in some wood chips. They'll burn up the oxygen before it gets up to temp and help keep scaling and pitting to bare minimum.

[oldred]

Be sure and toss in some wood chips. They'll burn up the oxygen before it gets up to temp and help keep scaling and pitting to bare minimum.



In this case I used some crumbled paper, there was very little room left in the pipe with all the parts in it. The capped end was a regular pipe cap like was screwed onto the bottom end but I used my lathe to remove the threads so that the cap was a fairly snug fit but would still fall off when the pipe was up-ended over the oil, the cap of course fell into the oil with the parts.

[MtGun44]

Wrap in stainless foil.

Bill

[MBTcustom]

You could just send it out? I've got a local heat treat house that has fully progressive ovens that are atmospherically purged through the whole process. Darn parts come out with a slight haze on them. Amazing!
Here's the place if you are interested. They have a minimum charge of $50 (which I've never exceeded) but with results like that, I'm not complaining. Great folks to do business with:
http://www.colemanheattreating.com/

[oldred]

You could just send it out? I've got a local heat treat house that has fully progressive ovens that are atmospherically purged through the whole process. Darn parts come out with a slight haze on them. Amazing!
Here's the place if you are interested. They have a minimum charge of $50 (which I've never exceeded) but with results like that, I'm not complaining. Great folks to do business with:
http://www.colemanheattreating.com/


Thanks Goodsteel I can use that service on occasion since heat treating some of the non-gun related AG parts I make has been a major hassle because the only close service has an expensive minimum and a "don't want to bother with you little guys" attitude. However in this case I had only three small pieces of O-1, a hammer, a sear and a small cam.

[MBTcustom]

Thanks Goodsteel I can use that service on occasion since heat treating some of the non-gun related AG parts I make has been a major hassle because the only close service has an expensive minimum and a "don't want to bother with you little guys" attitude. However in this case I had only three small pieces of O-1, a hammer, a sear and a small cam.

Well, Coleman is not a small operation, but it's run by a man who remembers where he came from. Also, he does quite a bit of heat treating for Wilson Combat if that matters.
It's a pretty large operation, but the last time I had a project that I needed done right, I spoke to the main man himself as the secretary took my order. All I had was two disk cutters made of 01 tool steel (used to cut out 2" diameter disks of leather or rubber). He apologized for the $50 minimum, but he said that he had to do it. I told him that seemed very fair for the quality of work I have received from him, and not to sweat it.
Getting it done right is worth a lot to me, and dealing with honest, humble people is worth even more.

[oldred]

Those people sound like the real deal and $50 minimum is very reasonable, even with the extra cost of shipping I will likely save a few bucks but even if I don't then just not having to deal with these arrogant A,,,,,, ,well you know, here locally it will be worth it! Thanks for the tip.

[Michael J. Spangler]

How about a couple good coats of white out.
Liquid paper baby!
I've used this to coat Damascus folder blades before heat treatment. It's titanium dioxide. Works well for a cheap coating for low temp (tool steel 1500 degree range) short soak steels like 01.

[M-Tecs]

Salt Bath heat treating or I pack them in my color case hardening mix. Doesn't color or add carbon but it does keep the scale off.

http://substech.com/dokuwiki/doku.php?id=salt_bath_heat_treatment

https://www.youtube.com/watch?v=9uPzc31bTD0

http://www.scribd.com/doc/16998084/Preventing-Scale-Loss-During-Heat-Treatment-Hot-Forging-with-images

Other options

Brownells http://www.brownells.com/gunsmith-tools-supplies/metal-prep-coloring/heat-treating-accessories/anti-scale-coating-prod23076.aspx

Enco http://www.use-enco.com/1/1/81923-anti-scale-compounds.html

[Red River Rick]

O1 is a oil quench tool steel and the upper critical temp is 1650 F.

So, wrapping it in foil doesn't really help much if you have to quench it. Some scale will form on it from the carbon in the oil.

I don't bother wrapping any 01 parts when I heat treat. Any light scale that forms gets cleaned off by bead blasting with "Glass" beads.

RRR

[dagger dog]

Borax, as in 20 Mule Team, it's a great flux it will melt and cover the steel and prevents scaling. You want the pure Borax and not a soap mix as Boraxo. It will blacken but is easily brushed off with a steel brush.

Our local Wally World stocks it in the laundry aisle.

[oldred]

Lots of good info here and I want to thank everyone for the suggestions. :cool:

I intend to try some of these methods, the borax trick sounds good and I will add that one to the things I am going to try. Appearance is the problem here and even light scaling was not acceptable for one of the parts since it was an exposed hammer that was to be re-polished and blued, the pipe trick worked this time but anything that can be used along with that would be added insurance. One of these parts I have been discussing here, the hammer, can be seen (barely anyway) on the "baby" high Wall rifle I just finished. Heat treating and polishing these parts was the last thing I needed to do prior to assembly, I posted some pics of the rifle in the single shot forum but of course the hammer is kind of hard to see.

[dikman]

Not sure if it would work for this application, but Japanese swordsmiths coat their blades with a clay mix prior to heating. Crushed firebrick and clay, applied wet and allowed to dry, is one mix I read somewhere. They use it to provide a hardened cutting edge and softer back without the need for tempering afterwards.

[M-Tecs]

DIY Anti-Scale Compound

http://www.bladeforums.com/forums/showthread.php/670773-DIY-Anti-Scale-Compound

[M-Tecs]

More info here http://straightrazorplace.com/forge/52196-anti-scaling-compound-two-thumbs-up.html