Cryo?

Both nickel and chrome are big tubby atoms but nickel is the winner at distorting the iron atomic lattice. The iron latticework is a nice repeating crystalline pattern of stacked atoms in straight lines, this allows those atoms to slide past each other and deform when needed (like when austenite transforms), but a big fat nickel atom in the middle of the mix skews all those straight lines around it, creating a log jam in the sliding action. Carbon does the same thing when trapped between the iron atoms when we super cool the steel to harden, like little wheel chocks keeping things from moving. put the two together and you can get the effect of trying to push an austenite truck up a chromium-nickel hill that is littered with wheel chocks so that you can get to the martensite on the other side. You then need a push from some extra cooling (sub zero) to get it over the hump. Chromium does this as well but it only takes a little nickle become problematic. I work with L6 all the time, but if L6 only had around .15% more carbon I would probably be freezing it due to its nickel content. At .75-.80% C the nickel by itself in L6 is not problematic. It is also worth noting that another Simple alloy containing nickle, 15n20, also limits its carbon content to .75%. Those eggheads making the steel kind of know what they are doing after all.:3:
 
Thank you Kevin - you help keep this old brain cells active with learning new stuff.

Ken H>
 
I know this thread is going on 2 years old, but I am trying to find out information in regards to cryo treatment in the knife making world. My research shows me that there should be a ramp rate to follow from ambient to cryogenic temperatures. There are manufacturers of such machines that I have been contact with, but I am curious as to how you guys are pulling this off, or if you are just dipping your ambient temperature blades straight into LN2 temperatures? Or if anyone has found a good supplier of these machines, at a relatively decent price? I found one in the US that builds a machine specially designed for knife makers for around $6k USD. Anyone know if this is a good price? Sorry for all the questions.

Thanks.
 
Old thread, but to add what I do..... I generally suspend blades above the liquid level in my tank for a couple of hours before submerging them. Then, after the treatment is complete they are laid on/covered with kawool so that they do not warm up too quickly. Generally for a couple of hours. Personally, I'm unaware of any knifemaker who has/uses the device you mentioned. I've heard of it the past, but never considered it, as the cost to usefulness ratio is just too high for me.
 
Thanks Ed. I can see how it might not be cost effective in the short term, but it sure would take some of the hassle out of it, and turn it back into a science. I read this entire post and see that there is still debate out there, but I had a friend who was studying this in school and passed me off quite a few papers in the day, and they always seem to be some pretty impressive results. However, I read that most are only doing their blades for anywhere between just a dunk, to 10 hours, but I was told 20 hrs minimum. Have you ever heard that rule?
 
I have heard the "20 hour rule" before, but in most cases that was applied to cross sections of steel much larger then would ever be present in a knife blade. I can't back it up with any science, but based on testing I've done, blades require at least a 6 hour soak to show noticeable affects. I've found that in many cases whenever someone states "a rule" about something, you must ensure you're comparing apples to apples, which in many cases where "rules" are established, that often is not the case, and in the process, much confusion ensues. :)

I've also found that from a knifemaking standpoint, there are steels that benefit from the cryo, and others.... not so much. I don't cryo plain carbon steels, as the benefits are very limited. Steels that contain higher alloy contents are the ones that derive the most benefit from cryo. It's certainly not any type of "magic bullet", so guys like me who do this full time have to weigh the benefits to cost ratio and make the decision whether the gains justify the cost and time involved. In the case of cryo, I do it to only those steels that I feel gain the most from it.
 
I know this thread is going on 2 years old, but I am trying to find out information in regards to cryo treatment in the knife making world. My research shows me that there should be a ramp rate to follow from ambient to cryogenic temperatures. There are manufacturers of such machines that I have been contact with, but I am curious as to how you guys are pulling this off, or if you are just dipping your ambient temperature blades straight into LN2 temperatures? Or if anyone has found a good supplier of these machines, at a relatively decent price? I found one in the US that builds a machine specially designed for knife makers for around $6k USD. Anyone know if this is a good price? Sorry for all the questions.

Thanks.


Interesting about the cryo ramp rate. I've never seen anything about a cooling rate that but it seems to make sense.
My ramp rate is to lower it slowly into the Ln so 5 to 10 seconds. Ed's method of suspending makes more sense but I always seem to be in more of a hurry than that. I always soak for at least 8 hours overnight, pull it and hang it in still air to warm up.
 
Interesting about the cryo ramp rate. I've never seen anything about a cooling rate that but it seems to make sense.
My ramp rate is to lower it slowly into the Ln so 5 to 10 seconds. Ed's method of suspending makes more sense but I always seem to be in more of a hurry than that. I always soak for at least 8 hours overnight, pull it and hang it in still air to warm up.

Ok, so I am not sure how much background everyone has on heat treatment and more specifically, cryogenics, but I have a little. I have read a few books - I know, not the real world, but...- and a few studies on the process. If you're interested look up "Cryogenics", by William E. Bryson. He also has some great books on "Heat Treatment, Selection, and Application of Tool Steels" is a great one that I am sure anyone/everyone on here would find relevant. I have also read this from Jay Fisher:

"What is the specific rate of cooling for most of these steels? 4-5 degrees Fahrenheit per minute. That means in order to reach -100°F, it should take about 40 minutes (from room temperature), and to reach -325°F should take about an hour and a half (from room temperature). This is why simply dipping blades into cryogenic baths of dry ice and alcohol or liquid nitrogen is a huge and destructive error, yet knifemakers who are uneducated in this process frequently do this, and tell others that it's the proper way to quench! Sad, truly sad for the knife client. The cryogenic process cooling rate is absolute and critical." http://www.jayfisher.com/Heat_Treating_Cryogenic_Processing_of_Knife_Blade_Steels.htm#Quenching_Rate

Which seems in line with what the books and studies say. So I am now "fishing" all the forums to see how other knifemakers are making this a reality....but so far, I have yet to find anything.

I am super interested in hearing any feedback you might have.
 
Last edited:
I've read so many different opinions on cryo that I don't know quite what to think.

If dry ice treatment is not the waste of time that some makers seem to think....it is probably closest to a controlled ramp (depending on how you setup)?
 
Ok, so I am not sure how much background everyone has on heat treatment and more specifically, cryogenics, but I have a little. I have read a few books - I know, not the real world, but...- and a few studies on the process. If you're interested look up "Cryogenics", by William E. Bryson. He also has some great books on "Heat Treatment, Selection, and Application of Tool Steels" is a great one that I am sure anyone/everyone on here would find relevant. I have also read this from Jay Fisher:

"What is the specific rate of cooling for most of these steels? 4-5 degrees Fahrenheit per minute. That means in order to reach -100°F, it should take about 40 minutes (from room temperature), and to reach -325°F should take about an hour and a half (from room temperature). This is why simply dipping blades into cryogenic baths of dry ice and alcohol or liquid nitrogen is a huge and destructive error, yet knifemakers who are uneducated in this process frequently do this, and tell others that it's the proper way to quench! Sad, truly sad for the knife client. The cryogenic process cooling rate is absolute and critical." http://www.jayfisher.com/Heat_Treating_Cryogenic_Processing_of_Knife_Blade_Steels.htm#Quenching_Rate

Which seems in line with what the books and studies say. So I am now "fishing" all the forums to see how other knifemakers are making this a reality....but so far, I have yet to find anything.

I am super interested in hearing any feedback you might have.

so much depends on the steel involved. the makers of basic stainless steel such as 12C27, 13C26, and AEB-L recommend a freezing treatment, cooling the blades to -95F, with no soak as part of the heat treat process.(http://smt.sandvik.com/en/products/...-12c27-piece-hardening-deep-freezing-70c-95f/)
Crucible recommends freezing treatment, cooling to -100F, to reduce retained austenite when using CPM S35VN, CPM 154CM, and similar steels.
Carpenter recommends freezing treatment, cooling to -100F, to reduce retained austenite when using B75P, BG42, 440C and similar steels.
here is a study using A2, where some samples went from room temp directly into LN2 http://www.airproducts.com/~/media/...-quenching-of-steel-revisited-33005019GLB.pdf
 
Scott - good links you've posted. From my discussion with Sandvik engineer they have found there is NO improvement in LN treatment over dry ice treatment. He talked like they had tested pretty thoroughly to determine this.

On the 2nd link - very interesting read there. Sounds like they did some good testing on A2 grade tool steel. Not sure their tests would apply to any other steel alloy. Two things stood out for me in their conclusions.
*********
1. Experimental heat-treatment schedules applied to A2 steelconfirmed that cryogenic quenching results in a moderateimprovement of wear resistance and hardness, at the cost ofimpact resistance.
**********
Note it's only a "moderate" improvement, and at the cost of impact resistance.

***************
2. Results confirm that, in order to be effective, cryogenictreatments need to be carried out soon after martensiticquenching from austenitic temperatures and beforetempering
******************
Note they are saying cryo must be done ASAP after quench.

That paper confirms what I have read other places - need for cryo depends on the steel, and if you are going to do it, be sure it's right after quench.

"IF" I remember cryo is for high alloys (tool steels, stainless, etc). Simple carbon steels (1080, 1084, 1095, etc) don't need it "IF" the HT/quench are done correctly. I do get things mixed up sometimes so please correct if this isn't a valid statement.

Ken H>
 
with the steels I listed, they were all recommending about -100F. i would bet if we could find a complete CCT on these steels, the Mf or martensite finish temperature is somewhere around -70F, especially since they all say no soak. hardness improvement at expense of impact resist seems to be the story in all research I have been able to find. time to break the dry ice and everclear, maybe make some PJ when knives are done.
 
Full on "Cryo" (LN2 -300F) is said to allow for the formation of small "greek letter" (it's all greek to me!) carbides that precipitate upon tempering (if the alloying is there). "Sub Zero" (dry ice -100F) is not cold enough to do this.

The main reason to use "sub zero" or "cryo" is for the retained austenite conversion over to untempered martensite, however, and some of the more highly alloyed steels have Mf points below -100F (dry ice won't get it as well as LN2 will). That said.....Martensite finish temperature (Actual Mf) is, from my research, a point of diminishing returns (you never get there).

Also....some steels like A2 have been shown to have their Mf well below -100F, D2 as well. Which I find interesting...as the data provided by the manufacturer of higher alloy steels say that Mf is -95F etc. You wouldn't think A2 would have that much RA after a standard quench, and I would think A2 would have all RA converted with sub zero (-100F) temps, but that's not necessarily the case....http://www.hypefreeblades.com/forum/viewtopic.php?f=3&t=928
 
^Well put. I personally don't like or recommend the Acetone/dry ice thing, simply because I've done it, and when compared to using LN, there's a very noticeable difference in favor of LN (on those steels where "cold treatments" matter)
 
general questions/observations not in any specific order:

The effects of cryo/cold treatments seem very subjective and possibly the best proof is anecdotal (not a bad thing but perhaps observable improvements are due to corrective ability of cold treatment over faulty heat treating)?

dry ice is less effective than LN?

You cannot lower blades into LN slow enough to be considered any kind of "Ramp"...merely break prevention?

cold treatment and heat treatment are vastly different. NO-ONE soaks their blades in a furnace for twenty hours. Perhaps ramping is less critical in a cold treatment?

If you were a mfg of commercial freezers you would push the necessity of cold ramping since that is something joe garage dude cannot do? (yes, cynical... I know...)

perhaps cold treatments are being done just to say they were done as a fine blade can be made without them if HT is dialed in? But if customers want something....?

dry ice has no effect on a blade?

dry ice is very effective on a blade?

Once you try LN you never go back to dry ice?

Everybody agrees that heat treating and tempering a blade correctly makes it a better blade?

opinions vary greatly as to cold treatment making a better blade? (and likely will for years to come?)
 
Last edited:
Ted, if you go back and read the posts (I know they are confusing) you will notice that everyone (almost anyway) says the need for cold treatment depends on the steel being used, with simple alloys not really needing any cold treatment. It's the higher alloy steels (tool steels, SS, etc) that benefit from cold treatment.

Dry Ice bs LN? Well, again it depends on the steel. I do think the knife steel manuf's have a decent idea if their steel requires LN, or if dry ice is sufficient. If a person is setup for LN, then it surely won't hurt for any high alloy steel, nor should it "hurt" a simple alloy.

Sandvik for example says they have tested their blade steels with LN and find no benefit over dry ice. When I say "dry ice" I'm referring to a dry ice/alcohol slurry, not acetone. There are other manuf's who recommend LN treatment.... all depending on the steel alloy.

Yes, a decent blade can be made without any cold treatment, but cold (DI or LN) does seem to have higher alloy steels.

On the idea of ramping down - never really heard that mentioned before for knife blades. I do like Ed's idea of laying them on top of LN in the vapor to allow cooling before dunking in LN.

I do think it's generally agreed you should come from quench, allow to cool to room temperature, then direct to cold (DI or LN) treatment with as little time lag as possible.

Ken H>
 
Thanks Ken. I have read so much stuff the last couple years on certain topics that some of it becomes a jumble of opinions. I have kind of gotten to where I learn here and at the hypefreeblade site. (that is mostly reading archives not interacting like here). The reason is I have gotten to where I don't have time to vette out 300 people for veracity. the tone here seems serious/friendly. anyway....

I'm planning on using A2 and 440C and was hoping to do dry ice/alcohol treatment. I really want to do things that matter not just appease potential customers because they demand something that provides marginal benefit. If LN is what really makes the difference I should be heading that way.

Yet even the the A2 doc looked like leaving the blade in air for 24hrs before LN gave the best blade. I think that was N2? ( And of course I ask WHY does it seem like everybody quenchs A2 in oil??) If you do a batch of blades and you're pulling them out one at a time to oil quench how over-soaked is the last blade? Wouldn't a rack of blades being air quenched be an advantage over the chronology of one at a time in oil?

Sometimes I read the cryo stuff and my head swims....Maybe because I'm still dialing in heat treating. Often when I get to really read stuff it's late and the brain is gone. And by stuff I mean technical stuff where vocab is unfamiliar and requires more thinking than telling someone "beautiful knife!"...I must be getting old...lol.

the LN fumes to pre-cool seem excellent. I also wonder if just putting the blade in a freezer and then in the fumes would help slow the "ramp". That'll get you to -20 and maybe slower that hovering over LN. though enough distance would give you good control there. The data on ramp speed seems like the goal is slower than easily achieved?

feeling old and tired today....
 
Ted, take a look at the top of page #5, and you can see it's actually better to go from quench to LN. Because of the way it works on a molecular level you want a constant drop of temperature from quench to LN with no pauses between.

For A2 tool steel note they also say at bottom of page #5: "applied to A2 steelconfirmed that cryogenic quenching results in a moderateimprovement of wear resistance and hardness, at the cost ofimpact resistance"

That's only a moderate improvement in wear resistance, but at the cost of some impact resistance. I think in chopper knives I might prefer to sharpen a bit more often and not worry about chipping so much. In a slicer the loss of impact resistance wouldn't be a problem.

440C I won't comment on - I've not done enough reading to give a good idea of importance of LN.

LN vs Dry Ice - consider the amount of improvement vs the number of knives you expect to make per month.... and cost.

Ken H>
 
If you are using dry ice as a cryo, I'd suggest using RV anti-freeze rather than acetone. It's non-toxic and non-flammable and cheaper.
 
Ted, there is nothing subjective about it. Take a steel and like A2 and do the "standard" HT, 1750F 30 minute soak, plate quench, then take a hardness reading. Then, do either a sub zero or a cryo treatment, and take your reading again. You will find, on average, a 2-3 point gain in hardness. The goal is to have the highest hardness you can attain post quench, then temper back. It's not subjective at all, it is actual material science. The reason the hardness gain happens is because the retained austenite in the steel is being converted over to untempered martensite (that then must be tempered). If your steel has no gain in hardness by sub zero or cryo, then there is probably no real benefit (other than the eta carbide precip with LN2....and data on that aspect is very scarce).

I would say that LN2 is probably BETTER than sub zero (dry ice/denatured alcohol), especially if you're doing lots of knives, for a few reasons. And I don't do cryo, only sub zero on the steels that need it like A2 (I send off higher alloy to Peters). 1. You can be ensured of 99% of RA conversion on most any and all steel with LN2. 2. You get the benefit of eta carbide precip which is said to aid cohesion of the martensite/carbide matrix 3. It's a chunk of $$$ for the dewar up front, but generally lasts maybe 3 months and is ~$60 a fill, compared to ~$10 worth of dry ice every time you need to HT, and is evaporated in ~24 hours. Numbers are approx. Point being, it's probably more effecient for a knife maker, especially in quantity, to use LN2 over dry ice sub zero.

Another example....a steel as simple as 1095. If you do the "right" HT for that steel (1475F, soak, fast oil quench), you will not see any gain in HRC reading by either sub zero or cryo. Why? Because you have 66-68 post quench, and thus, basically speaking, ALL of the austenite you put in solution is converted over to martensite during the quench. If you HT at a higher temp, say 1550, your post quench hardness will not be as high, maybe 64-65, and then to get back up to 66-68, you can do a sub zero or cryo treatment to convert the retained austenite (that caused the lower hardness) over to untempered martensite.

What I find amusing is the charts out there claiming that "Wear Resistance" is increased 400% (like on O1 for example) by LN2. I find that laughable. That would translate to having to spend 4X the amount of effort in hand sanding a blade that has been cryo vs one that hasn't, and that is simply not the case.

The idea is RA conversion, and tempering before sub zero or cryo will tend to stabilize RA, what we don't want to happen. With all that said.....if you find no improvement in the performance of your blades by employing said procedures, then I would say skip it. There are a few well known makers I can think of that use high alloy steels (steels that have excessive RA post quench), that do NOT employ ANY sort of sub zero/cryo, and their knives are raved about. Ponder that!
 
Back
Top