D2 / Cryo HT Question

[gull wing]

It's been a good while since I've done this, so hear goes.

Will Cryo improve D2 greatly for this blade? USAGE = *.098" thick x 3 1/4" long, folder blade, medium duty use, as in(cardboard, sisal twine, pine stick, apple)

Basically is it worth my time?

 

[Nathan the Machinist]

Yes. But it needs to be done before even a snap temper.

 

[Stacy E. Apelt - Bladesmith]

Yes, it is worth your time.

D-2 has a high amount of RA. You need to do sub-zero or cryo to get a higher amount of martensite.

 

[gull wing]

Thank you. I will do it.

Please forgive me, but what is RA?

 

[Shawn Hatcher]

Please forgive me, but what is RA?

Retained austenite. And just so you know, Nathan is probably the world's foremost expert on D2 and getting the most out of it for cutlery applications. He's a great asset to have here.

 

[Nathan the Machinist]

^ well I don't know about all that...

but yes, D2 needs sub zero as a part of the quench to avoid stabilized retained austenite. This, and a relatively rapid quench, allows you to forgo using the secondary hardening hump which taken together resolves the edge stability issues and makes it a high performance knife steel.

 

[me2]

Nathan have you tried the multiple quenches in D2? I saw an article a while back that showed considerable carbide refinement, but required 7 quench cycles. Optimum results were obtained using oil, but that sounds risky.

 

[DukeHarley]

Nathan, is there a heat treater you would recommend who would do this process for D2?

Jay

 

[Nathan the Machinist]

Nathan have you tried the multiple quenches in D2?

I've experimented with prequenching and while I've seen the grain refinement they talk about I haven't noticed changes to the carbides (I'm not sure that I would notice) nor have I noticed improvement in performance as a result of the finer grain. Beyond a certain point I'm not sure that finer grain does a whole lot.

I haven't done seven cycles though.

I have also experimented with prequenching above the recommended temperature ranges and have seen some interesting effects that I don't fully understand that could perhaps be related to carbides, though these tweaks have behaved differently with different makes of D2 and could not be called reliable.

Of some significance I've seen that CPM D2 has not responded well to multiple quenches and higher temps.




an additional thought: In a highly alloyed steel like this, carbide size and distribution is largely dictated by concentration and location of the carbide forming elements which do not move with heat, and are therefore more or less locked in place. With enough heat you can start to dissolve a primary carbide, but it is my understanding that it will always return once it eats more carbon.

You can control the carbon in solution and the grain, but beyond a certain point the primary carbides are set in stone. I'm not sure you're going to be able to refine those carbides much without changing the manufacturing process.

It is my opinion that the majority of the gains you will see with D2 in cutlery applications will have to do with maximizing homogeneity (nice uniform cubic martensite throughout), minimizing RA and keeping the secondary carbides small and uniform (fast quench and tempering under 500). This is done with uniform grain more than ultrafine grain, and addressing its tendency to stabilize RA. I think some of the benefit of prequenching may have as much to do with austenitizing a matrix with dispersed carbon (reduced soak time) as it does with grain refinement, but I don't know. *shrug*

 

[BluntCut MetalWorks]

I've tried up to 9 quenches - trying to grain & carbide refinement. Out of a pile of D2(Aldo) & K110(AKS) experimental knives - one D2 & a K110 were quite successful. With diamond stone, edge get extremely sharp and stable at 10dps. No orange peel and microchip from carbide tear indicate carbide size ~1um. When I sharpened my Yoshikane SKD-11 (D2) 64rc petty at 20 dps, micro chips occurs (in use) easily with sizes as large as 60um. My 64.5rc K110 petty would whittle relatively soft wood w/o problem and cardboard fine too. ~1um microchipping when whittle dry hardwood (janka above 1000). Excellent toughness too, perhaps due to fine grain.

The bad part is I can only get 3 good grind passes - on the 2x42 platen - per new 80 grit ceramic belt before it dulls. s110v & s90v are more workable than my fingers burning D2. Also from my so-so resulted D2, I think TTT for D2/K110 gradually change with subsequent quench passes. btw - cryo instantly boost hrc + 2-2.5 right after hardening quench. Quenchant type didn't seem matter for D2 as long as below 20 seconds oil.

ymmv.

... have you tried the multiple quenches in D2? I saw an article a while back that showed considerable carbide refinement, but required 7 quench cycles. Optimum results were obtained using oil, but that sounds risky.

 

[gull wing]

Came to the right place.:thumbup:

 

[Stacy E. Apelt - Bladesmith]

I looked it up last night. Without sub-zero or cryo, D-2 will have 20% retained (and probably stabilized) austenite. Looking at it the other way around, the blade only gets 80% hard. I prefer my blades 100% hard.

 

[ggoose]

Yes. But it needs to be done before even a snap temper.

So continue the temperature decrease from the quench right into the sub-zero or cryo, then temper?

 

[Stacy E. Apelt - Bladesmith]

Yes.....

 

[ggoose]

Thx...