Cryo

D

db

Joined
Oct 3, 1998
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It was -17 this morning and it looks like it is going to be the same tomorrow. Should I put all my knives outside for a cheap cryo treatment? :D
I've heard wind chill doesn't effect non living items but it was -30 and lower.
 
Assuming any retained austenite will be transformed to martensite, I hope the non-steel materials can survive the temper you'll need to destress your knives. Otherwise, the cryo won't be your pal.
 
thombrogan said:
Assuming any retained austenite will be transformed to martensite, I hope the non-steel materials can survive the temper you'll need to destress your knives. Otherwise, the cryo won't be your pal.
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There is so much contention about this it is difficult to work through even if you can read the technical details. For example I assume that if you took as quenched steel and used deep cold you get basically 100% martensite. However, practically this doesn't happen. I have spoken to two metallurgists who specialized in steels, specifically even in knife steels and both of them noted that you can't use cold to fully transform martensite in the high alloy steels because the austenite stabilizes almost immediately with any delay and there is no such thing as infinately fast quenches with no delays. This is why Haaksonsen uses 950+ C tempers on RWL34 (stress on the +).

Now looking at the carbide precipitation issue is even worse because you have one side basically saying that it is akin to the discovery of steel itself and offers hundreds of percent performance improvement and another side which screams just as loud that is all nonsense. Then there is a rational side that sits in the middle and has published papers showing an increase in carbide of a specific high wear form and a corrosponding increase in wear resistance and decrease in impact toughness. This is of course complicated by issues of martensite formation and temper adjustment.

Then on top of all of this you have makers like Dozier who speak out against cryo, makers like Busse who is very positive on using cryo, and other makers who will use it on request but are pretty much take it or leave it. In short, it is a very interesting field to look at, but if you actually want to move beyond faith, it takes a massive amount of work to actually try to cut through the hype, from both sides and try to find the reality.

-Cliff
 
Cliff: As I understand it, the effects of cryo treatment were first observed by people who worked in cold climates.
I have a friend who recovered a knife lost in the woods during a fall hunt. After a cold winter, he found the knife and it was "different: (improved).
This happened over 60 years ago.

I believe bridge builders also discovered that applying ice to welded joints made the welds stronger. I am going from memory here-I have that info in a reference book that I can't find, but, I believe that is what happened.

As far as stabilization of Austenite, it is certainly possible to quench and then cryo, and provide a virtually "seamless" cooling from Austenizing temperature to minus 320F.

I have also observed firsthand the effects of cold on A2 blades that were overheated during HT, allowed to rest for several days, the placed in an ordinary household refridgerator. Ths result-An increase of 4 points Rc hardness.

Now, before you jump down my throat, let me quantify that the magnitude of the effect of cryo is certainly related to steel type and alloy composition. I am certain that the effect is more pronounced in some steels, but, in my considerable experience heat treating knife blades, I can say for certain that the use of LN2 will have some effect on virtually any steel, even if time is allowed to pass before it is performed.

The science of cryo is perhaps inexact. However, as an Engineer, I am willing to take what I observe at face value, without necessarily being able to quantity it or even explain it. My conclusion: Cryo has an effect on hardened steel, and can certainly improve the function of steel as used in a knife.
 
Is the temperature of a mere refrigerator or freezer enough to do any good? Looks like true cryogenic effects would take temps far below what appliances are capable of. :confused:
 
What is the lowest Mf of knife steels? From what little I've read, after quenching, temperature isn't as critical according to some. You have little time to get past the pearlite nose, but once you've done that and started martensite, it will continue as long as you remain below Ms. I've read a couple statements where it's said the transformation will continue, even at room temp, for a very long time.

What confuses me is that comfortable ambient temps, fridges, db's backyard, dry ice, or liquid nitrogen seem to all get the steel to make martensite, so do the critical temp control when austenizing, and the far less relevant time variable (the 8 hour soaked O1 with grain size comparable to Cashen's 8(?) minute soaked piece) get replaced with a linear scale of transformation rate for time/temp? Do you get the same result sticking a blade in a fridge over night, or just leaving it on the bench til next year to finish it?
 
rj martin said:
As far as stabilization of Austenite, it is certainly possible to quench and then cryo, and provide a virtually "seamless" cooling from Austenizing temperature to minus 320F.
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From what I understand, there will be stabilization during the cooling as well because it isn't infinitely fast, just like there is carbide precipitation during quenching so you don't get 100% carbon hardening that you would expect. Specifically I asked Landes why you could not low temper HSS and his reply is that there would be too much retained austenite so the hardness would be too low.

Now I realize this would be idiotic, if you were going to do that then why not just use a cold work steel. However I was mainly asking out of curiousity on what would happen, or if you had HSS but just wanted the best knife with no heat resistance. Would a low temper give you a better combination of toughness/wear resistance. Based on work he has done measuring retained austenite, it will not because it will stabilize too much. Now I do realize that it depends on alloy content, which also complicates it further.

I have also observed firsthand the effects of cold on A2 blades that were overheated during HT, allowed to rest for several days, the placed in an ordinary household refridgerator. Ths result-An increase of 4 points Rc hardness.
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That is exactly what ASM notes for A2, though they don't mention the effect of a delay.

As for people seeing performance increases, people are usually horribly biased and take no effort to remove them. Even makers who promote heavily work they have done to showcase their abilities usually don't even take the most basic steps to eliminate user bias so it is hard to really pay any attention to the results, especially when they are also usually vague with no precision bounding.

Phil in Alabama said:
Is the temperature of a mere refrigerator or freezer enough to do any good?
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Yes, see the work done by Johnston on rec.knives which includes standard HRC testing.

hardheart said:
What is the lowest Mf of knife steels?
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There isn't one in the absolute sense.

Do you get the same result sticking a blade in a fridge over night, or just leaving it on the bench til next year to finish it?
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It isn't time dependent, martensite transformation takes place at the temperature, no hold is necessary.

-Cliff
 
In Verhoeven's book he shows retained austentite after cryo with AEB-L after 24 hours and directly after the quench (or a half hour later or something, I don't remember). There was a reduction in retained austenite when doing it immediately after but there was no reduction after 24 hours. I'd have to say the austenite is stabilizing a little slower than immediately.
 
The low will be -21 Celcius tonight and probably for the next few nights here in Edmonton, Alberta. Anyone wants to send his knife here for cryo? :D
 
Larrin said:
I'd have to say the austenite is stabilizing a little slower than immediately.
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It is alloy dependent, AEB-L is a really low alloy steel and you can get very close to full martensite even with low tempers. According to Landes you can get 67 HRC, with the biggest problems being improper heating (rate), delays in quenching, lack of oil, wait before cold, lack of repeated cold/temper etc. .

hardheart said:
gah, someone just explain this to me...
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Any part in particular or do you want a summary of the entire thesis.

-Cliff
 
if you could condense the 91 meg file into a sentence or two :D

I dunno, I just don't get how you retain austenite below austenizing temp, and through martenizing. Just not totally understanding what happens with the carbon. Is it too short a soak time because of alloying content?
 
Cliff Stamp said:
It is alloy dependent, AEB-L is a really low alloy steel and you can get very close to full martensite even with low tempers. According to Landes you can get 67 HRC, with the biggest problems being improper heating (rate), delays in quenching, lack of oil, wait before cold, lack of repeated cold/temper etc. .
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Well I followed the Landes recommended heat treatment recently with a 350F temper and got 61 Rc (using a 1925F austenitizing temperature).
 
Landes is much closer to Austria than you are, Larrin. Therefore, AEB-L quenched in Germany needs less retained austenite to get that AUS feeling, but AEB-L in America needs more.
 
Larrin you better send that blade to me for the backyard cryo treatment.
 
db said:
Larrin you better send that blade to me for the backyard cryo treatment.
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Well I always thought sticking a blade in a dewar full of LN was pretty ghetto, but I appreciate the offer. :p When we're out of liquid nitrogen we usually just use the freezer to get as much transformation as possible.
 
:)
Don’t discount the mystic powers of my backyard cryo treatment. LOL
Seriously would setting a knife out in tempts below 0 over night really do anything? I’ll try it with an old BM ATS 34 a SAK and an A2 blade, but not sure how I’d really tell if there was a difference.
 
From the sounds of it it might help the A2, although I guess it would depend on how it was heat treated or whether it was cryoed before.
 
thombrogan said:
Therefore, AEB-L quenched in Germany needs less retained austenite to get that AUS feeling, but AEB-L in America needs more.
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Yeah plus german rock is way harder and Landes plays it during heat treatment. Than and the fact that :

1) 1925 F is the low end, ~1975 or so is used for maximal hardness
2) you lose 2 HRC immediately with less than ideal heating
3) AEB-L just barely makes full hard, no slop like 1095 which has way more carbon than necessary, so any variation in carbon/chromium and your hardness drops. Batch to batch you would expect 1-2 hrc shifts, just look at the tie line variation based on small elemental shifts.


Larrin said:
Well I always thought sticking a blade in a dewar full of LN was pretty ghetto.....
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From what I can tell, aside from asking people who sell the $50k coolers, there isn't any benefit on small cross sections like knives. The problem with liquid N2 is that it is actually a very poor coolant from a speed point of view. You can actually put your hand right in it and take it back out with no harm. I used to do this to demonstrate properties of conduction and barriers all the time in labs. Now however there are too many restrictions on such "demonstrations". Of course if you hesitate during this process then you become handicapable fairly quickly.

hardheart said:
from the knifemaker forum...
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I pointed that out a long time ago on SwordForums because of the constant number of assertions that Cryo has no effect on carbide precipitation and is just a martensite conversion process. This is absolutely wrong. However :

"Man will occasionally stumble over the truth, but most of the time he will pick himself up and continue on. --Winston Churchill"


-Cliff
 
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