Foil wrap when heat treating?

[dbb-the-bruce]

Not really a beginner but this is a novice question.
I've got a muffle oven and I've done some heat treating. First thing you find out is that unprotected pretty much everything oxidizes to some degree and it can be a pain to clean or or just plain bad.

I've tried the "wire cage with boric acid as a barrier" - it kind of works but can be tough to get right.

I've read that the same can be accomplished with SS foil. So I splurged and bought 25' of .002" foil labeled good for 2100F (I think).

As I understand, I just wrap the part up tightly and proceed. The foil eliminates the oxygen environment (very little air between part in foil) so oxidation is also minimal. So that's it, just works like magic?

How anal do I need to be about sealing the foil?
How tightly does it need to fit the part?
What about quenching? does the foil stay on and not make a difference or do I need to be able to peal it off quickly?
Annealing wouldn't matter as you don't quench just let it cool somewhat gradually.

So in short - I'm looking for practical advise on how to use foil this way. Tricks, tips, what to expect for results.

Thanks.

 

[mattthemuppet2]

I've not done this myself (no heat treating oven) but I've read that the second part to the process is putting a bit of paper in the wrap with the part. The paper burns which uses up the oxygen = no oxidation.

 

[dbb-the-bruce]

I've not done this myself (no heat treating oven) but I've read that the second part to the process is putting a bit of paper in the wrap with the part. The paper burns which uses up the oxygen = no oxidation.

That's exactly the kind of information I'm looking for!

 

[BladesIIB]

@dbb-the-bruce I have a short video about heat treating, right at 1:50 I show how I make my pouch with foil and as @mattthemuppet2 said, I put a piece of paper in there to burn off any oxygen. You don't have to watch the video, I make a pouch with about an inch clearance around my blade after sealing, fold all my seams over 3 times to seal them. I air quench and usually do that between plates in the foil. If you cut the foil open right out of the oven too fast while the blade is still red, then it will still oxidize. You want it somewhat cooled before cutting it open. I don't anneal or temper in foil, since it is not getting hot enough to oxidize.Hope that helps, all the best with your projects.

 

[jcp]

I did some heat treating in the shop I worked at. I did use SS foil. I packaged the part as tightly as practical and put a small piece of wood or paper or even used a cigarette butt inside the pack to burn up the oxygen in the pack. Worked just fine…part came out with little or no scale.

 

[benmychree]

I worked in a shop where I did heat treating; the parts were placed in a covered box made of stainless steel that was filled with ground peach pit charcoal, later on, they could not find any more charcoal and switched to ground coke. This prevented scale and did not impart any significant carburizing effect, which did not occur to any significant extent due to the relatively low soaking times and temperatures at heat.

 

[MrWhoopee]

I believe that the s/s foil wrap is only useful for air-hardening steels. If an oil or water quench is necessary, the foil would interfere with the quench and the time it would take to remove it would allow the metal to cool below the critical temperature. I could be wrong, it happened once.

 

[BROCKWOOD]

Having no practical experience, I'll only add that Keith Rucker & Clickspring have covered this several times on their YouTube channels.

Ground peach pit charcoal in a dedicated stainless box sounds cool. Spring is right around the corner! (As an aside, I gather shells straight from my dinner plate for inlay work.)

Also Stan on the You Tube channel Bar Z uses an argon gas blanket in his oven. Then foil etc are not needed at all. I bought the oven, but haven't had a need for it yet.

 

[ChazzC]

I could be wrong, it happened once.

I thought I was wrong once; turns out I was mistaken.

 

[pontiac428]

The foil will not have any impact on your quench. In thermodynamics, there is a property called heat capacity. It is similar to specific heat, but does not include a phase change. Stainless has a pretty high heat capacity, so it takes a lot of input to raise the temp of 1 cc by 1 degree C, which is bad, but it only takes some miligrams of .002" foil to wrap something like a 200 g cutting tool, which means it has a insigfreakingnificant impact on quench time. At least not compared to increasing the water volume of the quench bath by 5%, or maybe lowering the air temp in the shop by one degree F. The foil wrap is not a proportionate concern compared to the other controllable variables at play.