Stainless Steel Foil

Leu Custom

Leu Custom

Joined
Jun 2, 2007
Messages
1,354
Where do you guys personally buy your SS Foil for Air Hardening Steels? What type do you generally use ? 321 or 309 ? And for what steels?
 
I picked up my last roll from MSC. You can find it at Enco also. It depends on the steel you are heat treating weather you need the 309 or not. Look at the HT temps and then decide. I got the hotter of the 2 just in case, But I no longer do any air hardening blades so I have a bunch reserved for tooling.
 
Tracy will be where I get my next roll. The current roll came from Texas Knife Supplies.

--nathan
 
I recently purchased a roll which was 2 feet wide by 100 feet (200 sq feet) of 321 from a place for $195.00 + $16.00 S/H. What have you guys paid? I know texas knife sells half that amount for around $170.00 + shipping. The stuff I recently purchased works just as well as the TKS stuff which also worked great for the past few hundred knives.
 
Leu Custom said:
I recently purchased a roll which was 2 feet wide by 100 feet (200 sq feet) of 321 from a place for $195.00 + $16.00 S/H. What have you guys paid? I know texas knife sells half that amount for around $170.00 + shipping. The stuff I recently purchased works just as well as the TKS stuff which also worked great for the past few hundred knives.
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That's a very good deal. Where did you get yours? I paid $60 for 20 square feet of 309. Most of the time I don't use it so I didn't need that much.
 
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Be aware that 321 is the cheap stuff. Depending on the vendor, it may be "rated" for 1800F of 2000F. It has been known to fail well below 2000.

Just a warning. We recommend (and use) 309 for all heat treating, particularly because we don't do any air quench steels that harden below 1800.

Rob!
 
cotdt said:
That's a very good deal. Where did you get yours? I paid $60 for 20 square feet of 309. Most of the time I don't use it so I didn't need that much.
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I got it from Lyon Industries. Worked great for the A2 I just heat treated the other day. Not a bit of scale ! Seems to be almost pointless to use 309 unless you're doing something over 1800'F.

Lyon Industries rates it at 1800'F, but says it can handle 2000'F. Don't use anything over 1800'F so no need for me.

Just looked up some of the prices for 309 and 321. Some places really RIP YOU OFF !

If both 321 and 309 are both .002 thick, what makes 309 able to handle more heat? The mixture of metals in the foil?

The stuff I picked up has

Titanium Nickel Chromium Silicon Manganese Carbon
5 x C max 8.00-12.00 18.00-20.00 1.00 max 2.00 max 0.15 max
 
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Leu, it's the content of the steel. 309 and 321 are different grades of stainless steel that have been rolled into foil-thickness. I've had 321 surface weld (for lack of a better term) to CPM154 in small areas during plate quenching, making the foild pack a female dog to remove. Not a big problem, but it kept me from slipping the blade from the packet to check for straightness before it cooled too much, and I had to go back to the grinder for a few passes before refinishing. From my understanding, 309 doesn't have this problem.

--nathan
 
I'd imagine that even better than stainless foil is foil made out of the same steel you are heat treating. That way you avoid decarburization because in theory, stainless foil doesn't have carbon (0.03%) and can absorb carbon from your steel. I have no data to prove this but it's simple thermodynamics. So instead, having a mill to make your own steel foil from bars would be best.
 
I'm guessing there's a reason why they make SS foil out of Stainless Steel and not tool steel or high carbon steel or etc etc !
 
IIRC low carbon stainless foil does not absorb carbon as it has a high degree of chromium therefor no carbon migration. It is made from stainless to withstand the high temperatures oxidizing atmospheres.
 
Also since the material is in an inert atmosphere the is no oxidation thus no decarb. If you had a purging furnace the foil would not be needed.
 
A C Richards said:
IIRC low carbon stainless foil does not absorb carbon as it has a high degree of chromium therefor no carbon migration. It is made from stainless to withstand the high temperatures oxidizing atmospheres.
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Interesting. Thanks for the info. Do you know how it works? Carbon does react with chromium and form carbides, after all.
 
I do not remember the exact reference or mechanics. i skimmed a couple of my metallurgy books but the info is not in there. It may have been one of the posts by those who are much more knowledgeable than I. I do know that nickle acts as a definitive boundary and I think I recall that chromium acts as one also. Now the minimal amount of carbon migration that might occur during the heat treating operation would not effect the final outcome. That is if it is done in the foil pack and in an inert atmosphere. If you put a bare blade in then the function would not be carbon migration but decarb. Carbon migration is normally seen at much higher temps IE welding temperatures. A damascus billet could see complete carbon migration within 3 folds. That is at temps of 2300F+. When I was doing case hardening, which is essentially reverse decarb we had to use temps of 1750F and hold it there for 7-8 hours. This was to raise the carbon content to approx .5 to a depth of .05". I have not experienced any decarb problems using foil with all the O2 removed. I have had decarb on simple carbon steel and stainless I Ht'd in a open oven. So how the mechanics work, not sure, but the foil prevents rather than causes it.
 
A C Richards said:
I do not remember the exact reference or mechanics. i skimmed a couple of my metallurgy books but the info is not in there. It may have been one of the posts by those who are much more knowledgeable than I. I do know that nickle acts as a definitive boundary and I think I recall that chromium acts as one also. Now the minimal amount of carbon migration that might occur during the heat treating operation would not effect the final outcome. That is if it is done in the foil pack and in an inert atmosphere. If you put a bare blade in then the function would not be carbon migration but decarb. Carbon migration is normally seen at much higher temps IE welding temperatures. A damascus billet could see complete carbon migration within 3 folds. That is at temps of 2300F+. When I was doing case hardening, which is essentially reverse decarb we had to use temps of 1750F and hold it there for 7-8 hours. This was to raise the carbon content to approx .5 to a depth of .05". I have not experienced any decarb problems using foil with all the O2 removed. I have had decarb on simple carbon steel and stainless I Ht'd in a open oven. So how the mechanics work, not sure, but the foil prevents rather than causes it.
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Thanks for the info! So carbon migration should not be an issue if the steel (in stainless foil) is held at 2200F either?

Also, how deep is the decarb when an open oven is used?
 
Well since the 309 stainless foil is rated at 2100F if the foil pouch is still intact then the short amount of time at temp would not have a problem with carbon diffusion (went and did some additional research on the forum). Like I said I cannot reference an exact study so at best, until I can, it is only my memory (which has been known to be very short at times) with regards to carbon diffusion. Decarb is a function of oxidation and if there is no oxidation there is no decarb. When I did the open furnace the decarb was one or two file strokes deep. So how deep was that, well probably .005 per side. Since I did not have a means to to a microscopic analysis I can not say the exact depth.
 
Even if there were carbon diffusion, I'd bet money that the steel would still analyze within specification for the grade. It's not a real consideration in my opinion.

We use MSC and Enco also and I have never had a problem with their 321 failing on steels that treat in the 1900's. If you were doing steels above 2K then I'd have a second roll for it.
 
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