Edge width before HT AISI A2?

D

deloid

Joined
Dec 19, 2007
Messages
458
I've not worked with AISI A2 before. It hardens at 1750-1800 and air cools. Tempering is pretty straight forward.
This is for a leather splitter blade that has a single bevel of around 18 degrees. The bevel is 3/4" up to the spine (total width is 1 1/2").
I'm trying to find out how close to final I can grind the edge.
On my knives I have them ground to 10 thousands but I usually work in 1/4' vanilla steels like 1084/1095.
This piece came to me 1/8" thick and I seem to remember hearing that thinner stock is more prone to warping/cracking during HT. On the other hand, since it is air cooled there should be less stress on the edge.

I would appreciate any advice.
Thanks,
Dean
 
The guys at Peters told me to keep it to 15 thousands or more. I opted for around 30 which is typically where i leave it when I HT myself.
 
Ok...so Ill go with 20-25 thou edge.
I could use a link on the timing of tempering as it cools. I suspect that as the A2 cools to the tempering temperature then the tempering should begin.
 
I take A2 to .015 before HT, no problem.

deloid said:
I suspect that as the A2 cools to the tempering temperature then the tempering should begin.
Click to expand...

No, get it as cold as you can before temper. A2 doesn't have a huge problem with stabilized retained austenite because it does decompose pretty well, but it doesn't decompose into just martensite. A knife is not a thick stamping die, it won't hurt it to get cold before temper and you'll get a more homogenous structure which improves your fine edge stability.
 
per retired Paul Bos , I give my A-2 a snap temper for an hour then throw it in the sub-zero mixture .
 
^

Years ago I compared D2 heat treated by Bob Dozier (with a propitiatory heat treat) to D2 heat treated by Paul Bos (which followed industry standard and received a snap temper) and it was truly eye opening.

Paul Bos is a respected and competent heat treater, but just because he says something is so, doesn't necessarily make it true. The same is sometimes true for the books, the literature keeps changing.

I don't mean any disrespect to Paul Bos, but I don't necessarily see his views about snap temper as the final word. I recommend people try it for themselves and see.

Regardless, to start the snap temper as soon as the blade falls to the tempering temperature is incorrect.

deloid said:
I suspect that as the A2 cools to the tempering temperature then the tempering should begin.
Click to expand...

Starting the temper on a blade that isn't martensite yet is not going to yield the expected results. Unless you're going for something like bainite it should at least be cool enough to hold in your hand. But concerns about cracking are misplaced and I think one should attempt Mf before pausing or reversing temperature. Just my opinion...
 
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