D2 Air Quench?

David Schott

David Schott

Joined
Sep 27, 2004
Messages
3,041
Hello,
Haven't done D2 before. I see mentions of air or plate quenching. The blades I am doing are folder blades, 1/8" thick. I have two small aluminum plates maybe 4"X1" thick that would barely cover the blades, but don't think thats ideal.

Is a typical air quench literally just removing the blades from the oven after soak and putting them in front of a strong fan to cool? Any disadvantage to this over plate quenching beyond possibly a chance to correct a warp when plate quenching? Would an oil quench work or be too violent/overkill?
 
During air quench, surface oxidation can put on a black layer that you don't get with the plates. Prior to starting plate quenching, I quenched D2 with oil for several years with good success. Vegetable oil works fine since there's no hurry to get into the Martensite field.
 
Hi David - you can correct warp during air quenching as well, the steel stays in a plastic stage for quite some time. I have never oil quenched A2 like Stephen suggests, only air and plate. The A2 should quench fine in any moving air, it won't have to be a strong fan. Still air will work as well, but I would move the part through the air in the same way you might air cool carbon steel for normalizing.

If you're worried about warp, I suggest air or plate quenching.
 
For plate quenching most of us leave the blades in the wrap. For air quench you may need to remove the wrap to make the cooling faster and more even. Don't know for sure if this is necessary.
 
Thanks everyone! I'll do three blades, oil quench one, air quench one and try the plates with another and see what happens...Thanks for the tips!
 
I use small alumimun plates about 3/8 thick and i put them in the freazer over night to get real cold and use this to quinch.
 
4" square by 1" thick will work fine for a folder blade.

Keep the blades in the foil, put the foil seam outside of the blade so it doesn't hold the plates off the blade. Practice your technique beforehand so you can be sure you're getting good plate contact.

The rapid quench of plates or oil will improve the corrosion resistance in D2 compared to air quench.

BTW:

D2 retains austenite badly. Stay on the low side of the austenitizing temp and use a moderate temper temp to reduce RA if you're not using cryo or dry ice.

A better D2 HT uses a medium soak temp and low tempering temp - but you have to address the RA with LN or dry ice as part of the quench.
 
Nathan the Machinist said:
4" square by 1" thick will work fine for a folder blade.

Keep the blades in the foil, put the foil seam outside of the blade so it doesn't hold the plates off the blade. Practice your technique beforehand so you can be sure you're getting good plate contact.

The rapid quench of plates or oil will improve the corrosion resistance in D2 compared to air quench.

BTW:

D2 retains austenite badly. Stay on the low side of the austenitizing temp and use a moderate temper temp to reduce RA if you're not using cryo or dry ice.

A better D2 HT uses a medium soak temp and low tempering temp - but you have to address the RA with LN or dry ice as part of the quench.
Click to expand...

So low side, then midrange tempering if no cryo? I have no means to do cryo....unless the freezer will actually do anything....which I doubt.
 
Oil quenching D-2 is very risky. We tried this at the shop where I work with several material sizes from 1/8" to 1". The Q.C. guy did a Dye penetrant test and all pieces up to 3/8" had stress cracks. Most you would'nt be able to see after polishing, but the dye does'nt lie. Is there a way to prevent this? I air quench my D-2 blades hanging vertical tip down over a fan. They usualy check 65 on the rockwell tester and then get double drawn back to 59-60Rc.
 
JBS TOOLMAKER said:
Oil quenching D-2 is very risky. We tried this at the shop where I work with several material sizes from 1/8" to 1". The Q.C. guy did a Dye penetrant test and all pieces up to 3/8" had stress cracks. Most you would'nt be able to see after polishing, but the dye does'nt lie. Is there a way to prevent this? I air quench my D-2 blades hanging vertical tip down over a fan. They usualy check 65 on the rockwell tester and then get double drawn back to 59-60Rc.
Click to expand...

And the tempering temp to get you down to 59-60 will reduce RA too. If you're wanting 61-62 (this is a folder) RA is a problem.
 
David Schott said:
So low side, then midrange tempering if no cryo? I have no means to do cryo....unless the freezer will actually do anything....which I doubt.
Click to expand...


The freezer will do more than nothing. Mf for D2 is probably around -100F. 25is closer than 70 *shrug*.

But if you're playing with D2 I suggest you call around to local grocery stores and see if any have dry ice. My local HT does. It truly does make a difference. Not just in edge retention, but the edge angle it will support. D2 with cryo will support 12-15 deg per side, without, more like 20.
 
Cryo will lower the impact strength of tool steels like A2 and D2. If you do an extra temper cycle you can decrease the retained Austenite.

A2 cryoed at HRC 60 has a lower impact strength than normally tempered A2 at HRC 57 which is lower than A2 normally tempered at HRC 60.

http://www.airproducts.com/NR/rdonl...019GLB.pdf#search="cryogenic quenching steel"

Above, I did not say oil quenching decreases D2s corrosion, it it that exposure to air during quench causes oxidation.
 
You can also temper D-2 at 950 and still get 58 Rc. instead of 450-500 which gives you 59-60. This will greatly increase impact strength.
 
Are you sure that you have no means to do cryo? Checking the phone book here in the Mass. burbs (Hudson, Ma) I have a local store that sells dry ice. All you need other than that is a cheap cooler. Styrofoam will work if you don't insist on using acetone.
 
Steve,

I've read that airproducts report on cryo several times. I have a fair amount of practical experience with this subject and D2. D2 isn't the best steel to make an axe. If you're doing a lot of hacking and whacking with D2 - you may have used the wrong steel.

Cryo reduces over all impact strength. Big fat hairy deal. But for 99.9% of people using the blade, this is moot. The edge stability in a folder is vastly more important in use. D2 without cryo will have more edge roll and stability issues. The edge on D2 with cryo is a lot stronger and tougher because it is more uniform without the globs of soft austenite everywhere. A relatively thin hollow ground skinning knife in D2 at HRC 62 with -300 cryo will cut a small nail in half in one blow without any substantial damage. That is way better than most folks expectation who are used to stainless and it is enough impact strength for most users.



JBS toolmaker,

I've made plenty of tools with D2. The high tempering temperature will convert RA. And that is a good HT for a stamping die. But all that RC test is measuring is the depth of a diamond penetrator, it doesn't tell you why. The secondary hardening hump is coming from carbides being formed from the carbon coming out of the martensite. You have softer weaker martensite surrounded by more and larger carbides. The improved ductility and abrasion resistance are a bonus in a die. But again, it still will not support a fine edge. Also, that carbon leaking out is gobbling up free chrome, reducing corrosion resistance.

I have seen D2 at HRC 62 suffer edge roll problems, not chipping (due to RA). And I have seen D2 at HRC 59 act chippy (weaker martensite and more precipitated carbides). The HT developed by industry for dies is not optimal for a knife. The best performance I have seen for D2 came from cryo as part of the quench. These are skinning knives that blow people away with their crazy cutting ability from their thin toothy edges, and outstanding edge retention even after cutting up nearly a dozen deer without touch up. D2 kicks butt, but you have to do it right.

just my .02 - hope I didn't step on any toes.

Thanks,

Nathan the D2 nut
 
If I sound like a blow-hard know-it-all, please understand I have gone through the trouble of making many many identical blades in D2 and subjected them to different HT and expended considerable time answering this question for myself. Low tempered D2 with cryo is better.
 
Nathan: If you did not have acces to dry ice...what would be your ideal heat treat for a folder blade in D2? Blades including springs. I heat to 1880, plate quench and double temper blades @ 500 and springs at 1200 if I remember . What says you?
 
I told myself I was going to stop getting into technical discussions on metallurgy on this forum. Mete and Kevin don't need me bumbling things up...

But one last time...

John,

A quench can be said to have been successful if you got under the pearlite nose. Eh? Well, in more complex steels there can be more to it than that. The rate of quench can effect where that carbon goes. A fast quench in D2 gives the carbon less time to interact with carbide formers on the way down. This can be good - giving you better corrosion resistance. But it can also lower Ms and Mf - leading to RA, leading to crappy edge stability. So if you're not going to use cryo (which is used to address RA which can be 15% or more), you may want to air quench without plates. You also want to limit the carbon you put into solution to only what you need for your martensite, also to reduce RA. So I'd soak it at 1,500 for 15 min, then ramp quickly to 1,800 for 30 min, then quench in still air. And I'd temper at 475 or higher, to decompose RA. You should experiment with your temper to find the highest hardness that doesn't suffer the edge roll that comes with RA. Edge stability is king - and with D2 high HRC and low RA are key.

That's a lot of talk about RA huh? Well, there are a lot of cool things you can do with D2, but many of them promote RA, which has to be addressed, which is why I use cryo.

I have thought about experimenting with a high temperature HT to get the carbon where I want it, followed by a low temperature HT to reaustenitize, but not free up as much carbon to raise Mf for the second quench and do away with cryo. Probably a dumb idea though....


Steve, there is a chart somewhere that shows a notched impact strength peak at something like 500 F and HRC 60, and several years ago when I started with D2 knives, that is where I started. Then I found another chart that had a different toughness peak at 800. And one that had a wear resistance peak at something like 400, and another at 850, and on and on and on. But how hot were they austenitized? Did they get cryo? A snap temper first? Then I found you can have two D2 knives at exactly identical HRC 62, and one has bad edge roll and one doesn't, depending on austenitizing temp, timing of cryo and tempers. Same hardness - way different knives. This is because of RA. Retained austenite is where that high impact strength comes from - it goes down from there because you're decomposing RA, and your increasing carbide volume. Well, that RA is good in a die, but really really bad in an edge. I finally came to realize that the "peaks" on those charts had no bearing on blade performance. The HT is different, so it is apples and oranges - and what they're measuring isn't relevant. Higher tempers decompose RA, but I think lower tempers with cryo are better.


Okay, I'm done this time. Really.
 
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