Heat Treating Questions

Whit

Whit

Joined
Dec 27, 2001
Messages
729
I have been playing with heat treating A2 blades in my forge. I know what you're all thinking............just send them to Paul Bos. I know, I do, but I'm messing around with this partly to try to understand the heat treating process. My questions are...

Do I leave the heat treating foil on or take it off for the air quench?

Can a blade partially harden? I mean not all the way up to 64-65 RC after the quench? Some of mine seem to be about 60 right after quenching. Should I still temper those?

What are your tempering methods?

Thanks for the help.
 
Hey Whit,

According to Jim Hrisoulas in the Complete Bladesmith These are the properties of A-2. I have never messed with it myself. It doesn't say anything about using foil.

A-2

forging: 1850 to 2000 degrees

hardening: 1700 to 1800 degrees

quench: air

tempering: 350 to 1000 degrees

Rc hardness: 62 to 57

Hope this helps a little.

Hillbillychuck
 
Hello again,

Same guy says in his other book the master bladesmith that if you are trying to prevent oxidation and scale formation on air hardening steels to make a mixture of borax and water and coat the blade and let it dry before you start forging and then to add more anhydrous borax as needed during the proccess. I think the foil would probably be easier on the lining of your forge though. Maybe try it both ways and see which one is better?

HillbillyChuck
 
Tempering is not a step that should ever be skipped. The tempering step helps convert retained austenite to tempered martinsite and helps add toughness to the steel. Stainless tends to have more retained austenite after heat treat because of its properties and can really benifit from a good sub-zero quench also. I've witnessed RC gains as much as 5 points from a sub-zero quenching stainless. Always temper in the oven after a sub-zero quench.

The purpose of the foil is to prevent scale formation on the stainless. If you remove the foil to quickly you will have scale form on the steel. This isn't a problem if you plan on regrinding the whole blade but some makers perfer to go right to the finish step from heat treat. Your best bet would be to do a blade and leave it in the foil for the air quench and then test it to see if the desired results are obtained.
 
I've found that right after the hardening, for some time, it's still setting up. I even do some straighten as soon as I can handle it. it I believe becomes harder as it sets, this is one reason why you should temper very soon after the hardening and straightening SS after cooling.. then nitrogen soak then temper again at least these two times.on 01 type steel you don't need to nitro and you can temper it after hardening anytime you wish.
I hope this helps
yes I agree very much Nitrogen soaking is a big plus and well worth it. as much as 30% more edge holding and some say more
...154CM all the way ;)
 
Whit,
As a metallurgist aquaintance of mine once said to me, "if you are not tempering or tempering properly, you deserve all the bad things that happen to you" :cool:

Yes, send it to Paul Bos or another professional heat treater experienced in treating the material. That is because he has the right equipment. You can spend the money on a good heat treating kiln and get the same results with practice, but that'll cost you some pretty cash. The forge is not the right tool for the job when heat treating A2. Not any heat treatment for A2. You need precise temps and holding times for A2. Its not that you cannot get a hard knife or even a functional one at that, but because A2 was designed a certain way for a reason. You would be using a less than optimum method and wasting the material. You would be better off with other steels and getting better results.
Don't want to get you down. I'm encouraged to hear you want to know more about the heat treating process. But I'm speaking from experience. When I started out, I was doing the same thing, years ago. After just reading a basic ferrous metallurgy book, you will see what I mean and it will make sense.
I would suggest learning a simple steel like the 10xx series or even a LOW ALLOY steel like 5160 or similar. They will give you a better understanding and some fundamental knowledge of the process. I would highly recommend starting out with 1084. It will make as good a knife as any and excellent results can be consistantly achieved in the forge with practice. Also, its chemistry will allow for a larger variety of heat treating styles than many (non-10xx) steels. Since you'll probably be tempted to try many. :cool:
Best of luck to you.

-Jason
 
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