Foil or no foil? That is the question.

CAN SOMEONE TELL ME USING FOIL OR NOT USING FOIL TO COVER THE METAL BLADE IN THE HT OVEN IS GOOD, BETTER, BEST, OR DOESN'T MATTER? DOES IT REALLY MAKE THAT MUCH DIFFERENCE OR NOT.
WHICH BRINGS ME TO ALSO ASK SHOULD I JUST PURGE WITH ARGON WHILE HEATING IN OVEN? DOES THAT MAKE ANY DIFFERENCE OR NOT?

What sort of steel are you using?

My thinking is plain steel and low alloyed high carbon, where the time and temps are not too great I would say skip the foil. For highly alloyed and stainless steels where the temps are higher and soak times are longer I wold say use the foil.

That being said my experience is limited.

Charlie

01 and A2 and some 10series to start. Then hopefully on to damascus.

I heat treat O! without foil. I do not have experience with A2.

Charlie

I use 1095 & o1 and have never had Mike to mention using foil. For now I have my HT done by a pro, but HT is one on my bucketlist for 2013.

When the steel reaches critical temperature (austenitizing), oxygen and carbon love to mix and carbon loss from the blade surface occurs. The iron also oxidizes and produces scale. If you grind your blades thick enough to compensate, no protection from atmosphere is necessary. You simply grind away the decarburized material/scale to the finished thickness.

If you want to grind closer to finished dimensions or don't want the decarb/scale you will need some form of protection. Foil will do the job, but this also means removing the foil before the quench and that can take time. With the 10xx or 0-1 steels for example, you have several seconds to remove the foil and quench the blade. That may not be enough time to harden the material. For stainless you may have minutes before worrying about hardening problems. There are paint-on anti scale coatings you could use and now you don't have to worry about getting something out of the way before quenching, but you have to grind it all off before finishing. Purging a HT oven with a neutral gas is also a good way to accomplish your objective, but once you grab the blade before quenching you will have some time in the outside air before you can get it into the quenchant. All of these methods have their advantages and disadvantages.

I use salt baths, that provide controlled temperatures and no exposure to oxygen. But, that's like playing with a home made volcano. It also has some dangers and a more interesting learning curve (expense). I have a Paragon oven, have used foil and paint-on's and purged with gas. I've left blades thick and heat treated in a coal fire and water or oil buckets. They will all do the same job. Use what tools you have and adapt. Probably millions of good blades have been made by what we'd consider primitive methods even into the early 20th century. They were good enough then, they are still good enough now.

Thanks to all for your input. I do appreciate it.

For low alloy steels, they just go in the charcoal fire without protection.
For knives I use a metal pipe in the fire. The knife then goes in the pipe.
This allows more even heating and prevents bending of the knife. Without the pipe, the knife may bend if you pull it out, look at it, and then stick it back among the coal / charcoal.

There is some decarburization, but with a straight razor, you need to leave it thick enough anyway to avoid the blade from crumpling or tearing or warping.

And, what I did not mention, this is a time at temperature problem. The longer you leave the steel in the fire the more this activity is likely to occur. The higher the temperature the faster it will go. Don't put a blade in the fire and then answer the telephone...or wander off and get distracted by something else.