Effectiveness of Stainless Steel Wrap in Atmospheric Ovens

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nullack

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Nov 17, 2008
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Gday folks,

So how effective is stainless steel foil wrap in protecting parts during heat treating when using an atmospheric furnace? That is, from carbuisation and decarubusation.

How do the blades come out - can you close finish them then using stainless foil?

I have been using high pressure gas furnances with inert atmospheres but because it involves another party it costs money that I could otherwise save on.

Thanks
 
They come out looking like this.
IMG00141.jpg

But this is CPM154cm I have done carbon and it comes out looking more of a grey color.
 
It's carburization and decarburization ! It works fine as long as you wrap it properly.Exclude as much air as you can and fold edges double.
 
Has anyone tried purging the oven with argon gas? Argon is cheap and widely available, though a top-loading oven would be required.
 
I dont know mate, but I'd image you would have a control mechanism to purge it with argon once the door is shut.

Mete, do you also wrongly spell colour? hehe just joshing ya my friend Thanks for the info Mete, as always your advice its appreciated
 
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Nevermind, I did a review of carburization/decarburization and argon has nothing to do with it, it only prevents scale. What is needed is simply the right balance of CO/CO2 in the mix. If the balance favors CO then you get more carbon, if CO2 is favored then you get decarburization. For example, for 1095 you want 0.2% CO2 to maintain zero carburization/decarburization.

I'm not sure the stainless foil would do anything but prevent scale, the air inside the foil still mixes with the outside.
 
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Er, by the very nature of using an inert gas you dont get oxygen or any carbon type or any hydrogen or other reactants in the atmosphere. So the absence of it is very much the relevance of why inert gases are used to purge the furnace.

I have been using high pressure gas furnaces with inert atmospheres for this reason, plus the gas quench gives a nice finish and doesnt require additional work afterwards. Since Mete has confirmed the efficacy of stainless steel wraps when properly administered this could be a good way to save on production costs instead of sending it to a pro shop.

The last question Ive got is about how much follow up machining is needed on properly done stainless foil wrap? Can you put in a finished part prior to heat treat and not have to fiddle with in the hardened state afterwards?

Cotdt if the seal is airtight no air is going to get in and I dont see how there would be enough air inside the foil to be of consequence?
 
Yes the inert gas should work if the oven is completely airtight, but the idea does not transfer into the stainless foil wrap. Air enters and leaves it.

Unfortunately, argon won't purge CO2 as CO2 is heavier.

Edit: The ovens that are typically used by knifemakers are not airtight, that's what I mean about purging with inert gases not doing anything. The stainless foils would not be airtight. It would mix with whatever air is in the rest of the oven.
 
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The way the pro shops do it is to use a high pressure gas furnance to force the atmosphere out by forcing in highly compressed inert gas into the chamber at higher than atmospheric pressure.
 
nullack said:
The way the pro shops do it is to use a high pressure gas furnance to force the atmosphere out by forcing in highly compressed inert gas into the chamber at higher than atmospheric pressure.
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Well that would work, but I'm not sure how it can be done in the home. My original idea of purging with argon gas wouldn't work, and I don't see how stainless foils would work either. Depending on how much it mixes with outside air it might work to some degree, though.
 
Have you guys tried putting a piece of paper inside your wrap ? Its supposed to burn up and remove the oxygen inside the wrap.
 
Paper is not necessary .For blades enough air is excluded .For complex shapes we always added machining chips as a 'getter' [it 'gets' the oxygen !].

Nullack , I sometimes write it 'flavor[flavour] 'or 'color[colour] ' or 'program[programme]' so those with Brit english will understand !
 
It just works, and pretty cheap way to HT complex alloys...

Here is how I do my envelopes, I suppose this pictorial will help some newbies:
First I fold 2 times one of the short side of the rectangle and flatten with a rubber hammer... (pic1)
Then I put the blade (pic2)
Fold the long side once and fold it again from the middle of the fold. pic3 taken at the second fold step..
Fold the last short side twice and carefully hamer all the edges with a small hammer with light hits(you dont want to tear the thin foil)... (pic4)
Voila, the envelope is ready to go in the oven. (pic5). I use envelopes a couple of times it it is not damaged. I cut one short fold after quench and slide the blade, so if it is used another time it can be used for a shorter blade.. I sometimes put multiple similar sized thin and small blades in an envelope...
 

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I keep hearing that foil isn't airtight.

Why not.

I'd be willing to bet mine are airtight when I make 'em.
 
Brian Fellhoelter Knives said:
I keep hearing that foil isn't airtight.

Why not.

I'd be willing to bet mine are airtight when I make 'em.
Click to expand...

me too
also rusty my CPM154 blades (really all my blades in foil come out that clean or cleaner)
its all about how tight you make the foil pack and no i dont put anything in to eat the leftover air
 
I cant comment either way but what the ASM say is "These packing materials may carburize, decarburize, or be neutral to steel, depending on the heating temperature, the carbon content of the steel, and the density of the packing (also the particle size of the packing material). The principal aim of such materials is to exclude the decarburizing gases from contact with the steel. If oxygen is to be excluded, the packing must be very tight and the sealing of the container perfect, for most gases can diffuse through ordinary seals at a surprisingly rapid rate at elevated temperatures. Materials that contain carbonaceous substances are, therefore, somewhat better where this is the case. In the annealing operation, where scale is present on the bars as charged in the furnace, decarburization may occur unless a carbonaceous material is present. Needless to say, the presence of moisture in the packing material is not tolerable as decarburization will take place very readily."
 
I push all of the air out and double fold the wrap, they come out quite clean when quenched between plates. If you double wrap them they come out just about the way they went in. Some heat treating foils do seem to "color" the steel differently than others. Double wrapping is more expensive, but I don't know how many knives it would take to make it more expensive than setting up for argon.
 
Thats good to know AcridSaint that they come out pretty clean. So basically it works, its nice and clean, but you have to ensure that you fully seal the foil otherwise it wont work. Thanks guys :)
 
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