PDA

View Full Version : Effectiveness of Acetone/Kerosene and dry ice??



EdCaffreyMS
08-14-2010, 01:23 PM
Lately I've read several threads on various knife forums about folks doing cyro treatment with acetone/dry ice. Since Kevin is now on board, maybe he can shed some light on this issue...

If I'm correct, acetone/dry ice will only achieve about -108F?

I know what I believe (it's not cold enough to give benefit to a blade), but would like to hear what others think/know. (maybe I'm wrong about the whole thing) Personally I use liquid nitrogen, and after reading all the threads about the subject of acetone/dry ice, my take is that folks are wasting a lot of time, effort, and money for something that lends little or no benefit.

Am I missing something??? If so, please school me! :)

BossDog
08-14-2010, 01:56 PM
First, I always tell people to NOT use acetone since it is slow flammable. I tell them to use common kerosene. Much less explosive.

I have read two different studies on this. Both of them circa the 40's or 50's. Both showed dropping the temp to -90F had the desired effect but would take longer than the typical -190F liquid nitrogen gets. The point of these studies was a cost/benefit analysis of what cryo temp would work good enough to save expense. I think it works. I will do a side by side test later this summer to find out for sure. Based on what I have read, I think it will have an affect.

Everything else I've read always talks about about going at least -200F.

EdCaffreyMS
08-14-2010, 02:12 PM
That was the point of confusion on my part.....I too had always read that steel requires -200+ to realize any benefit from a cryo treatment...which is why I brought up the subject. Of all people, I'm certainly not one to believe everything in print, and often prefer to find out for myself, but in this case, since I use liquid nitrogen, it would be impractical for me to do it just to satisfy my curiosity, when I know from spectrographs that liquid nitrogen works.

I was hoping to provoke some input either way, and if my suspicions that acetone/kerosene and dry ice really don't do much, then maybe it could save some people the time/effort/money, by helping them decide whether to do it, or go to nitrogen. On the other hand, if it is an effective cryo treatment....then I'll learn something.

Kevin R. Cashen
08-16-2010, 12:02 PM
I will separate the topic into two distinct categories- cold treatment and cryo treatment, and then limit my reply to cold treatment for the correction of retained austenite instead of cryogenic treatment performed for a panacea effect for almost anything from harder steel to pyramid power, or any thing in between the marketers of the process want to sell.

The one proven problem that continued cooling beyond the normal quench does indeed correct is retained austenite. In years past in addition to Ms (martensite start) on the I-T curve there was also Mf (martensite finish) but the reality of nothing being 100% in the real world has lead to more conservative designations such as M90%. With almost any steel one can expect perhaps as much as 6% retained austenite, and we just sort of live with what we find as acceptable levels.

Martensite does not form like other phases in steel, carbon atoms do not move to accomplish its transformation, and in fact it is their entrapment rigidly in position that is responsible for martensite. Instead there is a complex titling and shearing deformation that must occur in order for martensite to form; this mechanism is very dramatic and as fast as the speed of sound, so time bears no relation to it, only temperature shock necessary to drive the process along. The successful quench is the cooling rate sufficient to overcome the austenite’s strength to resist this deformation, which is not a problem with simple gamma iron (forgive the large words, it just means a simple iron phase) austenite. But as things are added to the austenite the more resistant to the transformation it becomes, and one of the most common strengthener is carbon.

Austenite is a solid solution of carbon in iron and two things determine how much carbon is in the iron-
1. The total carbon available.
2. The amount of the carbon that is put into solution as determined by the soak temperature.

Here is a dirty little secret about I-T curves, in order to be accurate they need to account for the maximum carbon in solution, but that amount is not always good. Ms is a function of chemistry alone so an I-T curve may show Ms for 52100 at 350F but it is VERY important that you look at the data given on the soak temp for that particular curve, since that determines the austenite chemistry by how much carbon is involved. You can take a steel like 52100 and make its Ms 500F by cooler soaks, and by going all the way to 1550F-1600F you can make Ms be 350F or below. Well along with this Mf also moves around, from 150F to well below room temperature making it impossible for a normal quench to achieve maximum hardness.

Thus in a perfect world with simple steels we should not have to resort to cold treatments but, none of us are perfect and things can happen between ideal soaks and ideal cooling rates. For these steels just moderate cooling below room temperature may have significant effects. Of course one should be careful how many gains in hardness they boast about from cold treatments on something like 1095 because it really reveals more about their initial heat treatment than they may care to admit.

Carbon however is just the beginning, huge substitutional atoms (carbon is small and rests between iron atoms) like chrome or nickel will dramatically fortify austenite’s ability to resist the transformation and will push Mf much lower. So when we reach 12% Cr or better cold treatments will indeed require -200F for complete conversion depending once again on our initial heat treatments and definition of “complete conversion”.

So when industry discusses cold treatments they are really not even considering simple steels that may only require a trip to the kitchen freezer, since they would consider that as an error to be addressed or corrected in the initial heat treatment. Instead the direction, specs and write-ups on most cold treatments concern complex alloys that cannot achieve the higher rates of conversion by any other way than cooling as drastic as liquid nitrogen.

Ron Bendele
08-16-2010, 12:18 PM
Thank you Kevin for that information. If you don't mind I would like to say back to you what I think I got out of it and you tell me if I am correct or not.

With simple carbon steels like 1095, 1080, etc. they may benefit from a continued cooling after quench, even as simple as the freezer. This is because of how we heat treated it in the first place and should not normally be necessary.

With steels like 440C, 154CM, S30V, S35VN, etc., a liquid nitrogen freeze would lower the retained austenite the most. One may also reduce the retained austenite using a dry ice/kerosene freeze, just not as much.

Thanks,

James Terrio
08-16-2010, 03:45 PM
...The one proven problem that continued cooling beyond the normal quench does indeed correct is retained austenite...

I've read a boat-load of articles saying retained austenite is undesirable and that cryo-treatment helps reduce it in almost all cases. I've also read claims that LN increases toughness by 300% and I flat-out think that's baloney-sausage... not because I actually know better, but it just seems too extreme to be believable. Of course I could be wrong, I haven't tested those claims.


Carbon however is just the beginning, huge substitutional atoms (carbon is small and rests between iron atoms) like chrome or nickel will dramatically fortify austenite's ability to resist the transformation and will push Mf much lower. So when we reach 12% Cr or better cold treatments will indeed require -200F for complete conversion depending once again on our initial heat treatments and definition of "complete conversion".


...the direction, specs and write-ups on most cold treatments concern complex alloys that cannot achieve the higher rates of conversion by any other way than cooling as drastic as liquid nitrogen.

If I understand correctly, LN treatment is most beneficial on alloys containing high amounts of chromium. Your explanation is in line with other reports I've read on the subject.

My own limited experience comparing LN-treated "stainless" blades to others (all other factors being equal) does seem to show better edge retention and less susceptibility to chipping without making the blades noticeably more difficult to sharpen. I like that a lot, although I admit I don't really understand how it works.

I think you're saying that with simpler alloys, it's not necessary to achieve temps that low to convert the retained austenite. Is it therefore reasonable to think that dry ice would be sufficient for cold-treating O1, 1095, 1084 etc? Perhaps LN treatment on these types of alloys is overkill and a waste of resources?

On the other hand, does -100F treatment (dry ice) provide none, some or all of the benefits of LN on complex alloys like D2 and CPM154?

Sampson knifeworks
08-20-2010, 09:07 AM
Hello,
This is a great thread for anybody doing their own heat treating! I use dry Ice on all my stainless blades and usually get about 1 or 2 points higher rockwell by doing so. This tells me that it does work, but my goal has always been to achieve the manufacturer's full hardness out of the quench! I have tried the plate quench and very rarely got my steel to it's full hardness and have better luck oil quenching the 154cm & ATS-34 as per manufacturer's spec's. Crucible has reliable heat treat specs and when followed to the letter you should get your rockwells right in line with their charts. FYI, I do not use liquids with my dry ice, I just buy two squares of it, sandwich my blades in between the dry ice in a cooler and leave overnight. Good heat treating is all about time and temperature, even though your furnace tells you it's at a certain temp. double check it with another pyrometer and seperate thermocoupler! Thanks for hearing my two cents.
Sincerely,
Clint Sampson
Sampson Knifeworks

cdent
08-20-2010, 11:17 AM
...Here is a dirty little secret about I-T curves, in order to be accurate they need to account for the maximum carbon in solution, but that amount is not always good. Ms is a function of chemistry alone so an I-T curve may show Ms for 52100 at 350F but it is VERY important that you look at the data given on the soak temp for that particular curve, since that determines the austenite chemistry by how much carbon is involved. You can take a steel like 52100 and make its Ms 500F by cooler soaks, and by going all the way to 1550F-1600F you can make Ms be 350F or below. Well along with this Mf also moves around, from 150F to well below room temperature making it impossible for a normal quench to achieve maximum hardness...

Hi Kevin,

Would the carbon that's not in solution be tied up as carbide, and is it a desireable goal to try to get .8% carbon in solution for the quench even if the particular steel has a higher percentage of carbon in it. I'm thinking of the likely forging tool steels and not the air hardening types.

Thanks for the thoughtful post and sorry if I'm seeing it wrong, Craig

BossDog
08-22-2010, 12:22 PM
I was reading some where recently early in the history of modern steel production the Swiss were thought to have better steel than any one. The thought process looking back on this was they had stumbled onto "primitive cryo" by the lower temperatures experience by the steel in production in the dead of winter. There are have been several cutting tests done by knife makers comparing knives given cold treatment via dry ice and they have seen an increase in edge retention and hardness.

Kevin's thoughts on the increase in Chromium in high alloy steels offers an excellent explanation why dry ice helps with retained austenite transformation for some steels and liquid nitrogen seems to give better results for other steels.

I have been studying heat treating and cryo quite a bit lately. Without exception, everything I have read about a dry ice cryo process is that it is an accepted industry practice as a cost effective method of cryo treatment but in some cases some steels could benefit by an even lower temperature such as liquid nitrogen. The implication in each of these books/journals/studies is dry ice is good and will give you "improved steel" but lower temps such as liquid nitrogen is better and will give you better results. The difference between good and better is generally not well defined and that's the rub for the home heat treating knife maker.

Mike Krall
09-28-2010, 01:50 AM
Seems like there is a lot of this question still up in the air.

My understanding is, the normal steels a person would forge (10xx, 15N20, W1/W2, O1, O2, L6, 5160, 6150, 52100) do not have enough retained austenite to need cold treating, let along cryo treating.

In Kevin's example of I-T curve with higher and lower soak temps (amount of carbon in solution) and the change in Ms/Mf (lower soak temps lowering carbon in solution and Ms/Mf), a person can find enough retained austenite at room temp that cold treating is an advantage. Commonly a gain of 1-2 points RHc. That gain bringing the RHc up to the max. level you would find in a reference (like Heat Treaters Guide) for one of the above listed steels. If the steel is HT-ed to spec in the beginning, the room temp RHc will be at max range and cold treating won't gain anything noticeable outside of a lab... that is... not findable in use.

Likely the most problematic of the common forging steels for retained austenite is 52100. Partly it's the chrome in it but mostly a higher retained austenite level comes from knife maker tendencies to HT it quite a bit differently than industry does, it seems to me.

The other common forging steels with chrome can have slightly higher retained austenite if HT-ed in ways that promote it. That they are usually HT-ed closer to industry spec limits the amount of retained austenite to a level where cold treating is not necessary.

Of the above listed steels, only O1 has an "optional" recommendation for cold treating (not cryo treating) in Heat Treaters Guide. Kevin Cashen does not cold treat his O1 or O1/L6 damascus and he would if he could find the difference in use.

---------------------
An aside...

There seems to be a tendency to run low-end austenitizing temps in HT-ing and it seems the primary driver of it is to avoid grain growth. There are two things going on here, it looks to me. There is an advantage for a knife to have small grain size... for a hardness, a knife with smaller grain size will be tougher. To have small grain size a person has to make them small, then keep them small. I think this last is where "the phobia" comes in... avoidance of above low-end austenitizing-range temperatures in the heating-to-quench phase.

Two things... grain growth does not really become problematic until reaching 1695F - 1795F, and getting steel to the desired temp quickly shortens the time grains can grow in. There is more-middle ground in austenitizing temps that won't grow grains and won't produce significant retained austenite.
-----------------------

The other-than-forging-steels have higher retained austenite due to higher alloy content (commonly from higher chromium levels but not inclusively). All the "A" and "D" series steels have "optional" recommendations for cold treating (not cryo treating). The 440 series recommendation is to cold treat (not optional) "for minimum retained austenite and maximum dimensional stability (-100, +/-20) with continuous cooling from austenitizing temp".

Except for the 440 series, all other cold treating temps listed are at -120F.

I know other high alloy steels have cryo recommendations. I don't use them and I don't have industry reference to them.

Mike

Kevin R. Cashen
09-28-2010, 08:53 AM
...Of the above listed steels, only O1 has an "optional" recommendation for cold treating (not cryo treating) in Heat Treaters Guide. Kevin Cashen does not cold treat his O1 or O1/L6 damascus and he would if he could find the difference in use...

Yes, and it is worth noting that while I have no reason to follow up the quench with further operations based upon desired hardness, I do have friends who's opinion I trust that claim to gain toughness benefits from cryo in the same steels. I have had many discussions with them about the theoretical possibilities of highly ordered crystalline lattices and I intend to one day study and explore these possibilities. However the fact that I am in no hurry to get to that research displays the relevance to knife performance I feel it actually has. If all the initial heat treating is done correctly with these simpler steels, I view any legitimate changes that can be made with further cold treatments merely a curiosity to be explored after the important stuff has been dealt with.

Cliff Fendley
12-03-2010, 09:50 AM
I just got off the phone with a Carpenter Metallurgist following up on the availability of some more CTS-XHP.

Everything he has sent me on heat treatment and testing their product he never mentioned cryo so I asked him their thoughts on cryo. He said there is no advantage provided your heat treatment is correct. He actually said he felt like you sacrifice some toughness doing cryo on top of a properly heat treated blade.

Proper initial heat treatment is the key.

ARCustomKnives
01-06-2011, 10:38 AM
Ok.... Some of this "scientific talk" has gona a little bit over my head based on my limited knowledge of the subject at hand.

So can somebody give me a more straight forward explanation on heat treating (then cold/cryo) 1095 specifically?

I.E., is this a steel that benefits as much from staying overnight in a kitchen freezer as it does in liqued nitrogen? Or did I get that backwards?

Would there be an "increased" benefit as I drop to colder temperatures? (freezer vs. dry ice vs. LN)?

Or are you saying that for a steel like 1095: Though I MIGHT see significant results from putting my blade in a freezer overnight, I won't see very much more of a change from taking it colder than a freezer?

Sorry for my confusion on issues already discussed, and I apologize if information or questions have to be repeated for my sake!

Kevin R. Cashen
01-06-2011, 11:08 AM
I'll quote Cliff since he sums it up very well with-
...Proper initial heat treatment is the key.

With 1095 if you are seeing noticeable benefits from a kitchen freezer, you can improve your hardening operation and forgo the freezer, and it may be advisable since the freezer is only handling a symptom and not the real problem. If you go liquid nitrogen and deep cryo, the benefits are talked about a lot but nothing is definitively proven, there are too many guys saying it works to ignore, but there are way too many guys who really know their stuff dismissing it to take it without a big grain of salt.

James Terrio
02-05-2011, 12:20 AM
I just got off the phone with a Carpenter Metallurgist following up on the availability of some more CTS-XHP.

Everything he has sent me on heat treatment and testing their product he never mentioned cryo so I asked him their thoughts on cryo. He said there is no advantage provided your heat treatment is correct. He actually said he felt like you sacrifice some toughness doing cryo on top of a properly heat treated blade.

Proper initial heat treatment is the key.

I just got my first CTS-XHP blade (http://knifedogs.com/showthread.php?14390-ENDS-DEC.-22-8pm-3-500-Post-GAW-Carpenter-s-CTS-XHP/page16) back from my HT guy (http://www.petersheattreat.com/cutlery.html). It was part of a mixed batch of 440C, 3V and CTS-XHP, and I presume he cryo'ed (he uses liquid nitrogen) it along with the rest. I'll ask him on Monday. I haven't sharpened or tested the XHP blade yet but it will probably happen by Monday. Then again, the Packers are in the Super Bowl...

I'm curious as to how cryo would lessen toughness. I'm pretty sure that's the first time I've heard of that.

In the meantime, I can say XHP grinds very nicely. We shall see how it holds up.

Cliff Fendley
02-06-2011, 03:49 PM
I already know how it holds up, gooooooood:biggrin:

Kevin R. Cashen
02-07-2011, 08:35 AM
...I'm curious as to how cryo would lessen toughness. I'm pretty sure that's the first time I've heard of that...

I have gotten feedback from people over the years who hired out the service to see the differences that they found a decrease in toughness in certain steels. It is actually self explanatory when you look at it, austenite is as soft as phases get in steel, martensite is as hard as phases get in steel, convert retained austenite to martensite hardness goes up, strength increases, toughness decreases. This would be even more so if one failed to re-temper the converted martensite. This is not theoretical but easily demonstrated, while the claims of reordering crystalline lattice stacking with extreme cold resulting in gains in toughness is still theory, atoms are still pretty tough things to see beyond a scattered X-ray signature.

James Terrio
02-07-2011, 09:54 AM
Got it. Thanks as always!