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Heat treating without foil?

Erstwhile

Aluminum
Joined
Jun 27, 2017
Is there any negative side effects of heat treating air hardening tool steels without wraping them other than scale?A2 and A6 specifically

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In addition to scale, you may have softening of the surface due to decarburization. There was a thread here not to long ago about A2 parts that 1) looked oxidized, and 2) had a soft surface. Our collective best guess was exposure to O2 atmosphere during heat treat.
 
Has anyone tried the old-fashioned soft soap method for preventing decarb?
Over here in the UK, stainless foil bags or wrap are hard to come by - we can order some online, but they're shipped from the US or China.
So, would soft soap work for onesy-twosy parts? And what is the 'right' sort of soft soap? There's is plenty available from places like pottery supply retailers.
 
Why not the old method of a steel plate box and bone or charcoal ?

Or steel filings if you don't want to carburize.
 
Roach poison

I use powdered boric acid, sold as roach and ant killer. Heat the part up just a bit then dip it into the powder, which will stick to the hot part. When you continue to heat the part the boric acid turns into a thick liquid that coats the part. A water quench will cause the coating to crack and completely fall off. Oil quenching doesn’t always get rid of all of the coating, but what’s left is pretty easy to clean off.

Easy, effective, cheap, and available.

Dave
 
I use powdered boric acid, sold as roach and ant killer. Heat the part up just a bit then dip it into the powder, which will stick to the hot part. When you continue to heat the part the boric acid turns into a thick liquid that coats the part. A water quench will cause the coating to crack and completely fall off. Oil quenching doesn’t always get rid of all of the coating, but what’s left is pretty easy to clean off.

Easy, effective, cheap, and available.

Dave

This has worked for me in treating small part made from W1 and such. For A2 and A6 I might be inclined to cover parts with boric acid which necessitates putting the parts and powder in a container, I have used one made of stainless foil for this. Parts made form A2 or A6 will be hot for a lot longer time and the boric acid may run off. Some metals such as 416 can be eaten up by the acid. Not sure why one metal is eaten up and another not. Try a sample first.
 
Has anyone tried the old-fashioned soft soap method for preventing decarb?
Over here in the UK, stainless foil bags or wrap are hard to come by - we can order some online, but they're shipped from the US or China.
So, would soft soap work for onesy-twosy parts? And what is the 'right' sort of soft soap? There's is plenty available from places like pottery supply retailers.

I've used that on water and oil hardening. Basically you want a quality soap of better make. If it can be used for hand washing and gradually wear down to a sliver without either cracking or turning to mush (which cheap soaps do) it should be suitable. You rub it on as soon as the steel is hot enough to leave a streak of soap.
 
In addition to scale, you may have softening of the surface due to decarburization. There was a thread here not to long ago about A2 parts that 1) looked oxidized, and 2) had a soft surface. Our collective best guess was exposure to O2 atmosphere during heat treat.
I was afraid they would end up soft like that, guess I'm going to order some stainless foil, it's a pretty decent job but the parts are little less than a half inch square so didnt seem worth it to order 50 feet lol

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Could you put the parts in a piece of pipe with caps on the end? Maybe put some paper in with the parts to burn up the oxygen?
 
When hardening A2, does the speed of cooling matter?

Yes it does, a lot! Oil quenching A2 will leave you with a piece so hard that it will be difficult to temper it back to something reasonable, the part will also have very low toughness and may crack during quenching. Water quenching A2 is just a big 'no no'.

A2 quenching is best done by simply hanging the part in still air. Hanging is better than putting it on a flat surface as the side facing the surface will cool slower and the part will warp. If the part is big and needs support then cooling is on a steel mesh table is probably best.

Avoid cooling the part with a fan or compressed air as again this will cause uneven cooling and warping.

If you need to heat-treat without foil the simplest way I have found is to use an 'anti-scale' compound like ATP-641 from Brownells. This is basically a clay 'slip' (thin mixture of clay and water) that you apply to the part after thorough de-greasing. The clay dries on the part and forms a barrier. During the quench the clay will crack and spall off the surface, you do not need to oil quench to get it to crack. You can also clean up the final part by bead-blasting to remove any remaining clay without damaging the steel surface underneath.

With all that said: heat-treating in foil will still get you a better result and a better looking part. Even better would be to seal up the outside of your furnace and then plumb it for inert gas like Argon. A small flow of argon during the heating process will drastically reduce or eliminate scale/decarb.
 
I think it's only critical to be exposed to oxygen from like 1800/1650

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Any temperature over 400ºF will start growing an oxide layer on the part. Any temperature over about 900ºF will start causing decarburization/scale (albeit slowly at first). Best thing is to protect the part the whole way through the heating/quenching process.
 
I think what Gbent is referring to is when you use boric acid in an electric furnace, it runs down on the bottom and soaks into the firebrick. It is almost impossible to remove. Been there done that.
 
Gotcha, makes sense. The anti scale I mentioned (ATP641) is not borax based and is fine to use in an electric furnace. ATP641 from Brownells has worked well for me many times in an electric furnace with no noticeable ill effects on my furnace!
 








 
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