Cryogenic heat treatment and it's importance.

Kitchen Knife Forums

Help Support Kitchen Knife Forums:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
CB1968

CB1968

Senior Member
Joined
May 23, 2013
Messages
726
Reaction score
441
I am interested in all you KnifeNuts and most especially custom makers thoughts on heat treatment methods and the importance or lack theroff of a Cryogenic stage in the heat treat process, after talking to many custom makers it seems that this an important part of the process however I am also of the understanding that Cryo treatment is rare and/or seldomly used in the process from the Japanese makers, just curious on thoughts and opinions on this and what are the benefits if any of a heat treatment with a Cryo stage?? Cheers CB
 
I really don't know much about this, but as I understand it some steels require a cooling to cryo temps to complete the transformation of grain structure from austenite to martensite. I'm not sure if Japanese makers commonly use steel which requires this treatment.

Their habit of leaving forged knives sitting for a couple of years before finishing them may be their solution to the problem.
 
I think Devin is a great source to explain the benefits of cryo, having worked many steels in mono and san mai construction.
 
Thats really interesting about Jknife makers leaving their knives to sit for a couple years before full development.
 
Thanks for the input guys, judging by the feedback i can only assume that this is a topic that is not fully understood and or realised by many knife users but is probably fairly simple stuff to knife makers, so i welcome their input,please find below comments from a well regarded maker.

Any steel benefits from cryo, particulaly steels with chromium and other alloys. The biggest benefit - increased transformation from austenites to martensites - increased hardness, more uniform structure (because you don't have soft spots in your steel matrix), ductability, better edge retention, ease of sharpening, etc. If you ever heard of wire-edge, resilient-burr expressions, these are examples of retained austenites - stuff (trying to explain in plain english) that didn't converted to full hardness during cooling, and they cause trouble.
Cheers CB
 
Generally it's done on high carbon high alloy stainless steels for slight improvement in hardness and toughness. Low alloy high carbon steels gain little if any benefit from cryogenic treatment.

I believe leaving the blades to rest is to allow stresses formed during the quench/temper to dissipate.
 
orangehero said:
Generally it's done on high carbon high alloy stainless steels for slight improvement in hardness and toughness. Low alloy high carbon steels gain little if any benefit from cryogenic treatment.

I believe leaving the blades to rest is to allow stresses formed during the quench/temper to dissipate.
Click to expand...

Gaining 1.5-2 point Rockwell hardness in alloyed steel is no "slight" improvement.

All steels benefit from cryo, some in more converted austenites (hardness, wear resistance, sharpenability), and some in a better ductability. Toughness depends more on HT the temperatures.

San mai construction doesn't bode well with cryo because of the inner stresses, that might be one reason not many san mai makers use cryo, another is cost. Liquid nitrogen or dry ice/acetone is not cheap and need to be constantly replenished as it evaporates.

And yes, there is absolutely no benefit to cryo if it is done the next day - heard about some makers doing it to minimize possibility of cracking.
 
Doesn't higher hardness (strength) and higher ductility translate to higher toughness? I didn't realize the increase in hardness was so great, but I suppose every steel is different.
 
Higher hardness doesn't necessarily translates into higher toughness, in fact can be the opposite - micro-chipping is a result of an over-hardened steel (or inadequately tempered).

Improved ductability does translated to better toughness, but toughness overall will be determined by carbide size of the elements in the steel, and the grain size of the heattreated steel, so all these factors have to be taken into account.
 
CB1968 said:
Any steel benefits from cryo, particulaly steels with chromium and other alloys. The biggest benefit - increased transformation from austenites to martensites - increased hardness, more uniform structure (because you don't have soft spots in your steel matrix), ductability, better edge retention, ease of sharpening, etc. If you ever heard of wire-edge, resilient-burr expressions, these are examples of retained austenites - stuff (trying to explain in plain english) that didn't converted to full hardness during cooling, and they cause trouble.
Cheers CB
Click to expand...

Are these results you've experienced yourself with steels you've heat treated? Is this a solution for making a "C" heat treat an "A"?
 
That was my response to CB question on PM that he quoted here (OK with me)

I cryo treated following steels - A2, 52100, W2, AEB-L, D2, PM#1, PM#2 stainless. All showed hardness improvement of 1.5-2 RC points (not sure about W2 as I didn't specifically test it for hardness change, but I did cryo it and contrary to common belief, it didn't crack). So these are steels that I have personal experience with. However, a good heat treatment is not just cryo - it's optimal quenching and tempering temperatures, frequency, proper speed of the quench, proper anneal, proper conditioning of the steel for best state to quench from, etc. Cryo improves things, but won't fix a bad heat treatment - on contrary, it can sometimes amplify inner tension of the steel - had one steel split in two halves as soon as I took out of cryo, but it had to do with the speed of the quench rather than cryo itself. All these steels were mono steels. San mai doesn't bode well with cryo, as the inner tension can make the layers peel off each other.

As I stated in a previous post in this thread, Devin is an expert on many steels and he would give a better answer.
 
Marko Tsourkan said:
Higher hardness doesn't necessarily translates into higher toughness, in fact can be the opposite - micro-chipping is a result of an over-hardened steel (or inadequately tempered).
Click to expand...

Micro chipping is also often just user error or sharpening error... Just because a knife CAN get micro chips doesn't mean the heat treatment is incorrect. (Sorry if that is off topic at all just find it funny when people immediately assume there is a maker error because someone gets micro chips)
 
Cryo is actually detrimental to toughness. It doesn't improve it.
 
chuck239 said:
Micro chipping is also often just user error or sharpening error... Just because a knife CAN get micro chips doesn't mean the heat treatment is incorrect. (Sorry if that is off topic at all just find it funny when people immediately assume there is a maker error because someone gets micro chips)
Click to expand...

I am not saying it's incorrect or not intended this way by a maker, it's just not optimal in my opinion, particularly in the view that cryo doesn't improve toughness, but on the contrary, is detrimental to it.

So, if a cryo'ed blade is tougher (not chipping) than a not-cryoed in a similar steel, then you have two probable explanation (either or both) - one blade is quenched from (and soaked at) a lower temperature resulting in smaller grain size, slightly lower hardness and more toughness. Second, it has been adequately tempered, reducing the as quenched hardness by 2-3 points.

I never understood an argument that bad sharpening results in micro-chipping, no offense, but it doesn't make sense to me. Can you explain what that means? A stable edge will not microchip in any thickness. Have you heard of knives from reputable American makers microchip? I haven't.
 
Basically "sharpening error" as I understand it is to sharpen without a micro-bevel. Now what is micro-bevel? It's the way to thicken the edge to make it more stable - thicker cros-section less likely will chip, but it doesn't address my point - why it is chipping in the first place?

Anyway, it's an old argument, we have been here before. I won't convince some of you and you won't convince me, so we stay with our opinions.
 
Marko Tsourkan said:
So, if a cryo'ed blade is tougher (not chipping) than a not-cryoed in a similar steel, then you have two probable explanation (either or both) - one blade is quenched from (and soaked at) a lower temperature resulting in smaller grain size, slightly lower hardness and more toughness. Second, it has been adequately tempered, reducing the as quenched hardness by 2-3 points.
Click to expand...
I am confused because Larrin said the opposite of this from my understanding. Also, I don't know anything about cryo'ed vs. not cryo'ed.

Marko Tsourkan said:
I never understood an argument that bad sharpening results in micro-chipping, no offense, but it doesn't make sense to me. Can you explain what that means? A stable edge will not microchip in any thickness. Have you heard of knives from reputable American makers microchip? I haven't.
Click to expand...
From my experience with knives I have owned or used that some people get a bit crazy when thinning occasionally. Yes, I am saying at a difference thickness a knife can chip easily. If you were cutting a case of lets say leeks (nice and sandy) none of my gyutos would really chip (unless you hit a small rock or something like that) from doing this but I have owned or used a few knifes that were thinned way to much to where the edge would flex and yes, they would chip.

Bringing up american makers: I have owned: Kramer, Burke, Devin, Rader, Carter, Mario, Martel, Harner, Del, Pierre (close enough to us), Davis. I was also able to use a HHH, Don's, and one of your knives (have not owned one yet although I was 12th on your list)

I have had micro chipping issues with 2. One has a pretty factory edge on it and the other had a super thinned out profile. I ended up having to put a mirco bevel on them and then they did not have chipping issues. I hope that explains what I mean by sharpening issues.

If an edge wont chip at any thickness, do you think when you take a stab at single bevel knives they will not chip under any use? I can cut whatever I want and not worry about chipping? I have knives that I break down exports with to cut into ribeyes. I wouldn't dare doing that with a yanagiba because the edge is so thin and when i hit small pieces of bone and have to twist to get through the knife would chip because of how thin it is at the edge, no?

I feel you think all knives should hold up without any chipping no matter what the use is. The issue is many knives have very different grinds and do need to be sharpened and used in different manners. I find the idea of throwing a knife in an over to "fix" the heat treatment is silly.

I am glad you really like the knives you are making and you (and your customers) are very happy with the knives you are making. Hopefully at some point I will be able to own one and use it myself.
 
Marko,

Do you know any knives that ALL people have problems with micro chipping? Typically I find that when a few people have a problem with something that hundreds of people don't have a problem with, there is typically more to think about then assuming something is wrong with the discussed product.

-Chuck
 
Cryogenic quenching of steels is a very controversial subject.

A cryogenic quench is done after the initial air, oil, water, salt, brine, or plate quench, depending on the steel. There are some steels that respond better after the first temper.

Cryogenic quenching of steels after hardening and sometimes tempering does one or more things to steel. It reduces or eliminates retained austenite, stabilizes the steel against size change, and allows for the precipitation of epsilon carbides.

Cryogenic quenches do not refine the grain of the steel, or make the steel tougher.

Some steels were designed to have some retained austenite. Some steels do not benefit from a cryogenic quench.

Every maker should do lots of testing on his/her steel of choice to see if the knives they make will benefit from a cryogenic quench. The same holds true for the entire heat treating process.

The end user is the best test to see whether or not the makers heat treatment is right for any knife.

Love and respect,

Hoss
 
chuck239 said:
I am confused because Larrin said the opposite of this from my understanding. Also, I don't know anything about cryo'ed vs. not cryo'ed.


From my experience with knives I have owned or used that some people get a bit crazy when thinning occasionally. Yes, I am saying at a difference thickness a knife can chip easily. If you were cutting a case of lets say leeks (nice and sandy) none of my gyutos would really chip (unless you hit a small rock or something like that) from doing this but I have owned or used a few knifes that were thinned way to much to where the edge would flex and yes, they would chip.

Bringing up american makers: I have owned: Kramer, Burke, Devin, Rader, Carter, Mario, Martel, Harner, Del, Pierre (close enough to us), Davis. I was also able to use a HHH, Don's, and one of your knives (have not owned one yet although I was 12th on your list)

I have had micro chipping issues with 2. One has a pretty factory edge on it and the other had a super thinned out profile. I ended up having to put a mirco bevel on them and then they did not have chipping issues. I hope that explains what I mean by sharpening issues.

If an edge wont chip at any thickness, do you think when you take a stab at single bevel knives they will not chip under any use? I can cut whatever I want and not worry about chipping? I have knives that I break down exports with to cut into ribeyes. I wouldn't dare doing that with a yanagiba because the edge is so thin and when i hit small pieces of bone and have to twist to get through the knife would chip because of how thin it is at the edge, no?

I feel you think all knives should hold up without any chipping no matter what the use is. The issue is many knives have very different grinds and do need to be sharpened and used in different manners. I find the idea of throwing a knife in an over to "fix" the heat treatment is silly.

I am glad you really like the knives you are making and you (and your customers) are very happy with the knives you are making. Hopefully at some point I will be able to own one and use it myself.
Click to expand...

As i understand microchipping isn't visible to the eye just looking at the edge but will be seen under microscope, when they are visible to the eye and have happened for no reason to the edge they are most likely due to grainfallout, for exampel: high cromium or other alloy content in the steel and is a big grain that has lost it's grip.
microshipping is mostly found in steel with very high carbon content +1% due to grainstructure, primary carbides are formed in these steels and are larger then secondary carbides found in lower carbon steels below 1%. overheating steel is also a factor

putting a microbevel on the edge will make it a little more durable/stable if chipping is a problem

Hope i got this right due to my poor english writing, it took me over one hour writing this:eyebrow:
 
Great thread and thanks to everyone who has contributed with their knowledge, thoughts and opinions this is fascinating subject matter and something that seems to be misunderstood by many knife users, however I think it was well summed up in Devins post and that is, that its the end user that needs to be the judge of a good knife and therefore the heat treatment process.
 
You must log in or register to reply here.

Latest posts

Back
Top