Stress relief without carburization

The soak is more than adequate but of more importance is the duration of cooling.

would you have a suggestion of a proper temperature to hold them to before opening the furnace, or should I try to program a controlled temperature drop?

carbin deposition in electric furnace? Is it carbon deposition or scale/ rust ?

Did you try some anti-scale coating/ paints ? These are availanle and provides barrier against the corrossion attack.

The other way may be to carryout the bore honing operation after the SR, may be with 1mm or so allowance so that no machining stresses are formed.

Third choice may be to carry out your SR in some inert or vacuum media.

We are fairly certain that we have carbon as it is uniform throughout and is worse over 900 degrees. I think that 900 to 950 may work, but I have no idea of how long to soak them. I have used anti scale compounds in thr past and they do work, but during high production such as we had immediately after obama's election would be very cost prohibitive as we produced over 1000 barrels a day and did so up to July. As to honing, it isn't possible with a rifle barrel. The rifling lands in the bore won't allow us to do that. It is actually the rifling process that is causing the stress. To give you some idea of what that means, I pull a carbide .312 rifling button through a .300 bore. We pull .012 total, but it shrinks back to approx.309 after the button passes through and we get another .001 shrinkage during stress relieving.

As far as I can see the 1100⁰F (600⁰C) is a good combination for the thermally accelerated stress relief. reducing the temperature to 900-950 (500⁰C) may need some where around a 24 hours cycle. It may not be worth it optimum stress relief is supposed to be done at about 75⁰C below the AC1 temperature - about 725 (so we do our SR at about 625-650⁰C ie 1100-1200⁰F.

For you, as I said the choices are the inert gas atmosphere if you want to do the thermal relief.

Else why don't you try out vibration stress relief (VSR)- the suppliers claim the retained stress levels comparable to the thermal, and that with an added advantage of being zero distortion.

To be frank, never tried this one, though highly tempted and am going to procure one soon. The retained stress can be checked destructively or by NDT methods.

But why carbon is depositing? it should rather have the decarburising effect at this temperature in fact literatures recommend the surface protection to avoid decarburisation.

Try protective (O2 and COx free) atmosphere. Argon is a cheap solution for the whole procces.
To avoid redox and metathesis reactions on Fe FeO Fe3O4 O2, C and COx in presence of some catalysing impurity in your alloy

Hello all , I am curious as to if you are using any sort of seal on your oven opening? We have several annealing ovens where I work and they all utilize a water seal first while the atmosphere in side is purged with pure nitrogen through exhaust opening for some time before oven heat is turned on. Duration and temp of soak are determined by which particular product is in there. By purging with the Nitrogen when create a virtually Oxygen free environment to anneal in . This helps in keeping a near bright finish on the product. Don't know if this helps but just putting it out there!! Thanks

Seems to me that if anti-scale compounds prevent the deposit, but are costly to apply and remove, that it is worthwhile trying an inert atmosphere such as argon. Since the bore is the issue, you may be able to rig up a manifold where argon flows only through the bore during heat treat. This will save a lot of expensive argon - especially since you don't have an atmosphere furnace.

Fill the bores with argon and plug both ends.

Filling the bores with an inert gas and plugging them is theoretically possible. The plugs would have to be fairly leak tight and able to stand the pressure increase when the barrel is heated. I suggest it is easier to just flow the gas through the barrel at a low rate, maybe around 10 cfh.

Yeah, well, its not like they are going to get very hot....lots of silicon compounds can withstand 900 degrees. And we are talking rifle barrels here...not a lot of volume. But heat treating is very temperature sensitive, and I figured that it might be a bit difficult to heat the argon up to the right temp before moving it through the barrels, especially if it is in a crowded oven. A little spray of argon down the barrels, then a little plug of silicon in each end while it is still cold and easy to handle, and let it heat up nice and evenly overnight. No corrossion. No carbon fouling. Simple. And you can apply a nice black anti rust coating on the outside at the same time.

My bill is in the mail...

It looks like I may have to seal the furnaces and use some kind of gas to acomplish what I need. I will start testing next week. Thank you all for your ideas. I will let you know the results

Exactly. Don't dilly-dally. That is the only way. The rest is ancient practice.

We furnace 304 stainless parts to remove contamination. They are heated to 900°C in a 90% nitrogen 10% hydrogen atmosphere & always come out clean.