foil envelope opinions- but science, preferably

[Lorien]

I recently had a little controversy with an acquaintance regarding heat treatment methodology and I thought it might be a fun topic to discuss here. Apologies in advance if the topic has been discussed ad nauseam.

This fellow works for a mold making company, and his job is to heat treat their stuff so I guess he could be referred to as a professional heat treater. After I posted up a picture of a blade I'd heat treated on IG, he said that if I'm not putting a piece of combustible material in the envelope with the knife, then I'm wasting my time putting the knife in foil at all.

The point that I kept trying to make, before he blocked me, (lol) is that by combusting material in there, you're simply replacing the oxygen with carbon dioxide and water vapour, neither of which are significantly better for your steel than oxygen. Also, the less oxygen the better, so a carefully fitted envelope is probably the best option.

The stainless foil, I've heard, contains some form of titanium(?) which apparently does something mysterious to the oxygen in the envelope, making it all hunky dory.

Anyway, I've talked with people and have done some reading, and that has lead me to the conclusion that just the foil is enough, and that messing around with kerosene or paper or whatever is more of a waste of time and potentially damaging to my knife. But I barely know anything, so I'd like to hear as many opinions on the subject as possible.

So, what do you think?

 

[Earthcrack.Knives]

Over the last couple of years I've used 100' (x 12") heat treating 3v. At most 4 blades at a time, quench plates being the bottleneck.
I've tried many variations including a small amount of combustible material, no combustibles, talcum powder and without. In my experience there is no noticeable or significant difference in depth of decarbed steel, when using steel foil heat treating with or without combustibles or talcum.
I've ran a piece of 3/16" 3v at 2000f for 40min with no foil for giggles, the whole piece was thoroughly decarbed. Not one hard spot to be found.
In my experience wrapping higher heat aust steels is a requirement for protecting from decarb, adding a combustible is not.
Unsolicited shop tip, I buy the higher temp foil and use talcum so that it is possible to use the pouch a second time. The heat puffs up the pouches a bit and when cooled they tend to "vacuum pack" the talcum prevents the foil from "welding" together and prevents its destruction when removing the blade.
Your buddies assertion that not using a combustible is akin to not using foil is absurd, in my opinion.
Cheers!

 

[Storm W]

I'm not a expert on heat treatment but I know a bit about what's going on. Just to start there is a very limited amount of O2 in the envelope, that's the whole reason you use it. That O2 will react with something but it's a pretty limited amount. Just in general it's not going to do much. Think about how much fuel could be consumed by a candle if you wrapped it that tight. That is the max amount of material that can be affected. If there is Chromium in the blade it's going to be what's affected and unless it creates a nitride there is no problem. The chromium works by oxidizing, the same thing as rusting and will do it at room temperature so no harm no foul. The only problem with it forming a nitride is that it keeps the chrome from doing its job and that is to "rust" as fast as possible so it locks out everything else just like paint. Anyway how that titanium works is that just like the chrome it burns, rust, oxidizes before it hits anything else important. Imagine that you mixed cooking oil, diesel, gas, alcohol, acetone and butane and pot it in a jar with the lid on. What part would go up first? When they make welding rod they add silicone, and manganese (weak deoxidizers) or aluminum or titanium (strong deoxidizers) as sacrificial fuel for any O2 that gets through the shield gas. Anyway if you are going to grind it at all afterwards there is no problem but if you are worried then you can add something else that will go up first and if you are worried about water or something you could use some aluminum chips but anything like a bit of oil or acetone or wood chips or anything else that will go up first will use up any extra O2 in the pouch. This is close enough to welding theory that I can give some ok theory. I'm sure there are others who can tell you how carful you have to be to keep it from O2 but in a industrial setting where it is critical we do have color charts and we only worry about colors over pale yellow and you fix them by removing that surface and if it's really important we use something like a etching machine and or "acids" to get the chrome oxide surface established thick enough to handle whatever nasty stuff it's designed for. Hope that helps.

 

[Stacy E. Apelt - Bladesmith]

In home/hobby knifemaking, the amount of O2 in a properly sealed foil packet is insignificant. The streel will have a shallow amount of decarb at the most, maybe almost none. The blade will be ground again in finishing and this minute layer will be removed. I have never seen any benefit to putting in a piece of paper to "burn away the oxygen". Those using high temperatures and high pressure on the quench plates often add talcum powder to prevent the foil from welding to the blade, but other than that, the powder does not do any magic. Talcum powder is a magnesium/silicon/oxygen mineral with added fragrances and chemicals. Honestly, I am not sure the chemicals are that good for the blade, but as with the atmospheric O2, the quantity is so small that the concern is moot.

 

[Larrin]

There’s some good info here: https://precisionbrand.com/faq/tool-wrap/

Surprisingly it doesn’t specifically mention putting other things in the envelope but it does talk about the mechanism by which the foil works, and of course it doesn’t recommend putting things in the envelope. The stainless foil is made to work by itself, not to be dependent on something else. I don’t need other junk in there dirtying things up.

 

[Lorien]

There’s some good info here: https://precisionbrand.com/faq/tool-wrap/

Surprisingly it doesn’t specifically mention putting other things in the envelope but it does talk about the mechanism by which the foil works, and of course it doesn’t recommend putting things in the envelope. The stainless foil is made to work by itself, not to be dependent on something else. I don’t need other junk in there dirtying things up.

that's a handy link! Thank you all for making this such an informative thread

could you recommend any good books on the subject? I remember reading somewhere the rationale behind not using combustible material, it was in some book by a doctor of some kind or another. I took that rationale to heart, because I generally believe everything I read, especially if it's by a doctor or other smart type of person. You seem like the kind of guy who might have read a book about metallurgy, so maybe you know the one I'm talking about? All I remember is that there was a picture of a knife on the cover...