D2 Air quench temp?


Is there a preferred temperature for the air to be at with an air quench on D2? I guess what I’m asking is am I better to air quench over my forge for a few hours in the shop….. or hang it outside in the winter at -20 deg? And why?
I wouldn't hang it above your forge, if your forge is still hot. Just cool air, or Aluminum plates. Some people use a fan.
I've never worked with D2, but other "air hardening" steels are usually best clamped between aluminum plates - helps keep blade straight if nothing else.
Thanks for the replies guys.

Still trying to understand this. So “air quenching” will cool quickly enough to lock the carbon and you won’t benefit from quenching cooler to be harder, or longer to be more soft? So, it just is what it is?
There are just enough substitutional Cr atoms in D2 to retard corrosion but not quite enough to make it fully "stainless." But there is enough distortion of the lattice to resist the martensitic transformation enough to make retained austenite problematic. Slowing the cooling at all beyond what is necessary for hardening will only increase the retained austenite to increasingly higher levels. E.g. - the slower the air quench, the less complete the hardening process, and the more the need for post quench cold treatments to achieve full hardness.
Thanks Kevin. Very helpful information.

so what I’m hearing is I can still do a differential quench with D2. In other words, the ground thinner sections (roughed out edge shape) will quench harder because of quicker heat dissipation than the thicker sections. I just have to experiment to get it right.
Umm, no, that really won't work in the way you may be thinking. Differential quenches/hardening are the result of the formation of pearlite at the spine and martensite at the edge. In this case, the softer phase (pearlite) is the most stable phase possible in an iron-carbon system. D-2 cannot make pearlite, this is what makes it air hardening. So, what you will get is still martensite, but it will be mixed with austenite- literally one of the most unstable phases you can have. Yes, you will gain some toughness, but it will be because you have not completed the hardening process and should you get conversion of the metastable austenite later on it can be an issue in several ways.
Okay, darn. Thanks for making it more clear.
Sometimes I get an idea in my head, and I like to experiment, but I’m not too much an “hold my beer and watch this” kind of guy. Thanks for the info!
Could you just jam it into some vermiculite, like when trying to anneal other steels? Or does it have to cool faster than that?
Could you just jam it into some vermiculite, like when trying to anneal other steels? Or does it have to cool faster than that?
I’ve not worked with D2, but I have worked with a fair bit of A2, which has a pretty similar heat treating response from what I understand. A2, once you heat it up sufficiently, will get hard pretty much no matter what you do to it. If you try to anneal it like a conventional steel in vermiculite, it still is hard, but pretty crappy. There is so much RA that it doesn’t even stick to a magnet well, even though it will skate a file. I wouldn’t try slowing down the quench. It will get hard, but I’m willing to bet that you will get a terrible mix of martensite with tons of RA, a little perlite, and maybe some bainite. It’s not gonna be good. Larrin Thomas has some good info on D2.