How important is Cryo for A2

B

Brian.Evans

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I'm getting ready to have my steady rests heat treated here in town by a local machine shop. They won't need cryo, so I figured that they would be ok getting done in town. I was planning on sending my A2 slipjoint that is ready for HT to Peter's, but the guys at the machine shop said they would throw it in the envelope with my rests for nothing. However, they don't offer cryo.

My question: How much better it would the knife be with cryo vs no cryo? It's a Bose Zulu spear in 3/32" A2, planned to take it to about 60-61.
 
There are steels that greatly benefit from Cryo treatment and some that benefit less. A2 is one that benefits quite well from Cryo. It does not need it per say but does benefit from it. I personally Cryo all blades that I make.
 
Thanks Dave. I will go ahead and send it out for ht with cryo.

Honestly surprised there was only one response on this topic.
 
I've been very happy with A2 without cryo, but I haven't done comparison tests (would love to hear about well-documented comparison results). I prefer to temper toward 59-60 as insurance. I'd expect you'd want a spear to have more toughness than hardness and edge holding.

My new 'office' has a -80C freezer, but it's a thousand miles or more from where I heat-treat. :-(
 
daizee said:
I've been very happy with A2 without cryo, but I haven't done comparison tests (would love to hear about well-documented comparison results). I prefer to temper toward 59-60 as insurance. I'd expect you'd want a spear to have more toughness than hardness and edge holding.

My new 'office' has a -80C freezer, but it's a thousand miles or more from where I heat-treat. :-(
Click to expand...

I'd like to see side by side tests as well, but I haven't been able to find one yet. Every one I've talked to seems to think its a good idea, but no one is really able to prove it with definitive tests.
 
I just re-read your post. It's not a spear. It's a Bose pattern "Zulu Spear" as in spear point slipjoint. Just wanted to be clear.

20130705_200419.jpg
 
A2 is close to the bottom of the list in terms of cryo benifit. Actually has the potential to lower hardness and wear resistance if you don't get it to true cryo temps.

-Sandow
 
Repost since this ended up in a rather off topic thread.


Sandow said:
Was good meeting you all. If you guys ever need anything, just PM me if you didn't get my contact info at the bbq.

For those of you that were interested in the effects of cryo treatment, dial your BS filter all the way up and enjoy.

From asia (high probability of being a complete fabrication but might just be plagiarized) and not actually a published journal. That said, most of it seems possible.
http://www.kau.se/sites/default/files/Dokument/subpage/2010/02/48_671_684_pdf_16802.pdf

Slightly more believable paper but notably from an industrial source and lacking error bars for all of their charts which is a pretty bad sign. Their EDS output is BS but their SEM micrographs are decent. Interesting output in terms of loss of impact resistance but again, take it with a grain of salt. Even if this data is correct for this steel it doesn't translate to every other steel.
http://www.airproducts.com/~/media/...etals-cryogenic-quenching-steel-revisited.pdf

Review paper on the Cryo treatments. Also from asia and published in an online journal (will publish anything as long as you pay them to) but it is properly referenced. Figure 6 demonstrates what I was talking about hold time. After 30 minutes it basically doesn't make any difference for hardness. Table 2 has a good breakdown on steel comparisons with different soak temps. D-2 is a rockstar at 817% wear resistance and AQS is a redheaded stepchild at 4% decrease...
http://research.ijcaonline.org/iccia/number9/iccia1068.pdf

If the decrease in impact resistance does correlate with soak time, and given the trivial changes in hardness and wear resistance over time. Kinda looking like half an hour is the best trade off if you care about impact resistance.
-Sandow
Click to expand...
 
Few more just for a bit more depth:

Once again, a very marginal asian journal so be skeptical. More support for a trade off between hardness and toughness from cryo. Pretty spectacular difference in hardness for 316L if their data is believable.
http://www.idc-online.com/technical...cal_engineering/Material Characterization.pdf

In engrish, but their output for AISI M35 shows no real change in hardness or toughness but shows decent wear resistance increases.
http://article.sciencepublishinggroup.com/pdf/10.11648.j.ijmsa.20130202.14.pdf

Not sure why the only people that care enough to study this stuff are in central asia but here is one on M2. No impact resistance change, some hardening and solid wear resistance increase.
http://www.hindawi.com/isrn/tribology/2013/408016/

There only seems to be one thing that is consistent about cryo treating and that is that you'd better know what it actually does to the steel you are using and decide if the changes fit your application.

-Sandow
 
The short answer is, A2 is dang good stuff for knives. I don't see how cryo would hurt it, but I don't think it's mandatory.

Sandow said:
There only seems to be one thing that is consistent about cryo treating and that is that you'd better know what it actually does to the steel you are using and decide if the changes fit your application.
Click to expand...

I am a fan of deep-cooling temper cycles and cryo treatment to complete the quenching process. Mostly to convert retained austenite in high-alloy steels. That seems to be pretty well documented, and in my limited experience/testing, cold treatments do improve toughness, hardness and wear-resistance.

Other benefits are much more murky, especially in the relatively small sections and fairly simple geometries that we use. Claims of "500% increase" in this or that are - again, in my opinion and experience - nothing but hype. I will hazard a guess that cryo adds more like 5 or 10% performance to steel that is already very close to its optimum heat-treat.

The average knife user will probably never notice the difference between a blade that has been "cryo'ed" and one that hasn't. The really picky ones will.
 
Sand ow, that was from a thread on cryo in D2, right? I think I saw that. I've seen opinions that one down on both sides of the argument. I love a2, and use it almost exclusively.

I actually went ahead and gave the local shop that is HTing my stiddys the knife parts. I'll see how they do on this one. It is convenient at least.
 
No. Was from the Virginia blade smith thread.

I think you made the right choice skipping it with the a2 ;)

If you look at this one on page 5 table 2 you will see a2 near the bottom of the list:
http://research.ijcaonline.org/iccia/number9/iccia1068.pdf

The more I read, the less there seems to be anything to argue about. Seems to just come down to the steel you are using and the application you will be using it for. Sometimes it is helpful and sometimes it makes nearly no difference or is deleterious. The notion that it is always a good idea is clearly wrong though.

-Sandow
 
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