Sub-zero questions

Kev

Well-Known Member
#1
My go to steel is AEB-L. I have gotten some very nice results and testing has met or exceeded expectations in both designed tests and real world application. That said, I am still looking for ways to improve, and as of yet I have not done any type of Cryogenic treatments.
My question is this... At what point (temperature) does a "cryo" treatment become effective? That is to say, to achieve optimal results with AEB-L steel? I'm asking to find out if it is mandatory that I get an N2 dewar and N2, or if I can obtain the same effective results using a solvent/dry ice solution? I'm not necessarily looking to cheap out here, but any subsequent savings could be used for other things, knife related, that I would love to have LOL.
Thanks in advance.
 

EdCaffreyMS

Forum Owner - Moderator
#2
Although there are a lot of folks out there who use some type of dry ice solution to "cryo" their blades, I personally believe they are fooling themselves. Cryo is about converting retained austinite to martensite, and if done in LN (-321F is it's boiling point), will generally gain you 1-2 Rc hardness points when tested.

Based on my experiences, "solvent/dry ice mixtures simply do not get cold enough for any meaningful conversion/noticeable advantage.

I have good results with cryo on the more complex steels I use, but all of it is done in LN.
 

KenH

Well-Known Member
#3
Ed is correct on use of dry ice/solvent mixture for carbon steels. -95⁰F just isn't cold enough - and many folks say LN isn't needed for carbon steel blades. I don't know, don't have any experience in carbon steel and cold treatment.

For your question about AEB-L, the metallurgists tell us that all retained austenite will be converted above -95⁰F level, so dry ice/solvent mixture is all that's required for RA conversion with AEB-L type steels. What the LN (-321⁰F) level does for AEB-L (and other similar type steels) is produce a special ETA carbide that's really fine grained and improved wear resistance (it's said anyway). There is a good bit of question if it's enough to be worthwhile or not. There are some real experts out there who can better answer that question.

My thinking (make that "reading" of other folks experience) is if you're making a lot of blades, then LN is the way to go, from an economical standpoint because a dewar will last so long. Much better than running back 'n forth to store to purchase dry ice every few days. OTOH, folks like me who make a couple blades/month on average, Dry Ice works just fine and doesn't lose any quality on HT of blade.

Ken H>
 
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#4
When I hear intelligent experienced knife makers arguing both sides of something I opt for the side that both agree upon. In this case every knifemaker that thinks a cryogenic treatment is advantageous would agree that LN works....while not every Knifemaker in the cryo camp would agree that dry ice and alcohol/antifreeze/acetone/whatever else will hold the cold works. So the easiest way to not have one more thing in your head is....LN.

Thinking this way however....can get expensive. LOL! This is why I bought a heat treat furnace, higher end 2 x 72 grinder, Heat treating oils (fast and slow) rather than the myriad of agreed upon cheaper quenchants, etc.

Why do it this way? Because I am a second guesser....If I have inconsistent results It rattles me and my first thought is..."Which of my economic based solutions just bit me in the rump....?" Then I get mad at myself for allowing variables (that maybe I shouldn't have) to control a process that already has a learning curve without me rolling the dice to save a buck...then....I give up.

My first six O-1 knives were made 17 years ago....three of them worked fine...the other three? Meh....But I saved money not using expensive quenchant....and got discouraged and didn't make another knife for FOURTEEN YEARS....Lol!

So...our own personality plays into what we do...no? Quite a lot...

You know how YOU are wired...and therefore you know where your "line" is as far as experimentation with methods/materials. We should all proceed with caution....though we often don't..lol.

I value tortoise over hare..lol! Or, for me, LN it is....
 

BrandantR

Well-Known Member
#5
I've never used AEB-L, but I use a lot of CPM154. I've found that the dry ice sub-zero treatment does in fact raise the hardness level by 1 to 2 RC points as the literature suggests. I have a hardness tester and verified the results for myself. I don't have any local access to LN, but I can pick up dry ice at the grocery store.
 
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#6
I don't have any local access to LN, but I can pick up dry ice at the grocery store.
I have a neighbor that stores Bull Semen in his Dewar for a month or so every year....he fills it for me when I need it and since they go to town often (120 miles) he delivers! It lasts me about 6 weeks and is $72 to fill it.

Your test would indicate that the dry ice works fine for the AEB-L.
 

Kev

Well-Known Member
#7
Thank you for the responses, the knowledge shared is much appreciated. I am also one of those guys who likes to eliminate variables, and use known quantities whenever possible. One of my biggest pet peeves on social media forums is guys asking about buying a $20 saw blade at HF to make knives with. For $15 and $7 in shipping they could have a known metal with known elements and proven heat treatment procedures, but alas we all must learn.
I have a few friends at machine shops that use LN to shrink parts for assembly, so I may be able to leverage those relationships, to experiment, while saving up funds for my own dewar.
Thank you again for the advice and encouragement.
 

KenH

Well-Known Member
#9
Cryo/cold treatments don't always improve things. Wouldn't hurt to test vs a blade that's not been cold treated.
You are correct, Cryo/cold treatments don't always help some types of steel, especially simple low alloy carbon steels.

BUT - the OP asked about AEB-L and cold treatment will certainly help that. The RA doesn't get all converted at room temp, and needs something close to -95F for complete conversion. This only takes a few minutes at -95F, not hours. For the ETA carbides to form it takes Cryo temps of -300F or so and several hours at this cold temp for the ETA carbides to form.
 
#10
Cryo/cold treatments don't always improve things. Wouldn't hurt to test vs a blade that's not been cold treated.
Hi me2....are you saying that even if you get a point or two on RC scale it may not be worth the effort? My first A2 blade did not get cryo'd but still seems to work very well. One thing I consider is that regardless of outcome I can tell a potential customer it has been done...which may be a selling point.
 
#11
Good Lord. Sub zero and cryo are used for very specific reasons. Without getting into the "eta carbide precipitation" one gets from using LN2, and just sticking with WHY sub zero (-100f) or LN2 (-300f) are done, we can look at AEBL and it's martensite finish temp. Go to Bohler Uddelholm and look up their HT recommendation for AEBL. They offer a few choices, with no sub zero and with sub zero. If you choose to HT AEBL and NOT use either sub zero or cryo, your max HRC will be around 60 (give or take a point). When you actually FINISH MARTENSITE TRANSFORMATION (by going down to the Mf temp that the people who make the steel says it has), then you get a better conversion and a bump of 2-3 points in HRC. Try using AEBL at 60HRC. Try using another identical at 63HRC. It is like night and day. I don't get why some people just don't understand simple physics, and try to pass off that it isn't needed. We, as knife makers, are always attempting to get the max HRC post quench, and then temper down to the desired HRC. Another topic for another thread. The higher the steel is alloyed, the lower it's martensite start and finish temps are, and the colder you must quench the steel to convert austenite over to untempered martensite. Period, that simple, end of discussion.

OK so I tried to call up AEBL heat treatment from the manufacturer, but only could find 13c26 (sandvick's exact copy of AEBL). Without sub zero, you get 59HRC. With sub zero, you get 62HRC. That's 3 points difference. Which do you want to settle with? Me, I know what I want out of my steels...as much martensite transformation as I can get. After all, that's what hardened steel IS.

Lower alloyed steels have a martensite finish temp ABOVE room temp (all the simple carbon steels and tool steels up to and excluding A2). That is to say, going colder does NOTHING for the steel at all. Now, full on cryo with LN2 precipitates eta carbides, adding wear resistance, and is said to make a better carbide cohesion with the surrounding matrix. A lot of study has been done with LN2, and more is needed, as there is even some disagreement between research as to what LN2 actually does to steel (besides a near 100% martensite conversion for all but the most highly alloyed steels. Think T15 for example).

There are sooooo many posts on sub zero and cryo and why they are done. Here and elsewhere.
 
#12
Rick just resurrected this link from a while ago...SamauriStuart and ken H helped me a bunch on that thread....I'm old and this stuff does not stick in my mind so a good re-read for me and probably helpful for the OP of this thread.

As I'm working on leather right now(love/hate...uhhh...maybe jus hate)...my head is not too much in the HT zone...so sorry if I was seemingly not paying attention. I actually have print-outs from K Cashen and SamuariStuart....

https://knifedogs.com/threads/cryo.40538/page-5
 
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me2

Well-Known Member
#13
Hi me2....are you saying that even if you get a point or two on RC scale it may not be worth the effort? My first A2 blade did not get cryo'd but still seems to work very well. One thing I consider is that regardless of outcome I can tell a potential customer it has been done...which may be a selling point.
No. I'm just saying there is some testing that indicates cold treatment/cryo doesn't always lead to better edge holding. Bfc member Hardheart did some CATRA testing a couple years ago and compared some high alloy steels, S30V and some others. He also compared the same steel with and without cryo. About 60% of his samples did better without cryo treatments. Details can be found by searching his username there. My takeaway was it's not a good assumption that cryo treated blades always perform better. I don't know of it would with AEB-L, but it's not as simple as cryo/cold = better.
 
#14
My go to steel is AEB-L. I have gotten some very nice results and testing has met or exceeded expectations in both designed tests and real world application. That said, I am still looking for ways to improve, and as of yet I have not done any type of Cryogenic treatments.
My question is this... At what point (temperature) does a "cryo" treatment become effective? That is to say, to achieve optimal results with AEB-L steel? I'm asking to find out if it is mandatory that I get an N2 dewar and N2, or if I can obtain the same effective results using a solvent/dry ice solution? I'm not necessarily looking to cheap out here, but any subsequent savings could be used for other things, knife related, that I would love to have LOL.
Thanks in advance.
as mentioned, AEB-L/13C26 recommend a sub-zero(-95F) treatment immediately after quench to room temperature. the idea is continuous cooling, the sub-zero must be done within 30 minutes of reaching room temperature.https://www.materials.sandvik/en/pr...-13c26-piece-hardening-deep-freezing-70c-95f/. so to answer your question, solvent/dry ice should be enough.
if you read this thread https://knifedogs.com/threads/cryo.40538/ you will lots of references about sub-zero and cryo. Cryo has been around a long time and the verdict is still out on what is does. check here https://www.cryogenictreatmentdatab...chilling_toughens_metals_increases_tool_life/ this article is from 1955. the database even sorts articles by the steels discussed.
IMHO, there are few accepted tests that reflect knife performance. CATRA shows how well you can cut sandpaper. Charpy impact shows how hard you have swing a hammer to break the steel. none seem to reflect how a blade will behave in the "Real" world.