Is CRYO treatment the new edge packing

JTknives

JTknives

Blade Heat Treating www.jarodtodd.com
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Jun 11, 2006
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So I have been wondering if cryo is all it’s cracked up to be. And by cryo I mean -320 Liquid nitrogen. The reason I am starting to question is because of what I have seen in steels response to it and subZ as well as all the heat treat data and research. Out of all the heat treating data sheets I have seen and looked at I can’t think of a single one that says to use cryo. Tons of them say freeze or subZ aka -100°f but not a peep of -320. What I have always heard around the forums is a long cryo soak precipitates ETA carbides. But from my research this is false as ETA carbides are formed during the temper cycle.

According to one paper I read thy stated that carbides actually grow larger as the temper temp goes up. So now that has me wondering if what we thought we where gaining with a cryo treatment and low temper is just the benefits of converting retained austenite and then bringing out the ETA carbides with the low 300-500° temper. I have heard that cryo increases hardness but honestly I have not seen a hardness difference on the testing I have done with cryo vs subZ. To me hardness is a multi factor variable that’s mostly affected by retained austenite. If that’s being converted over at the subZ then what is cryo doing for the steel after that?

I know this might be a little out there but I just feel that there is a lack of data to support claims that cryo does what people say it does. Just remember back in the day I remember when edge packing was the topic of conversation. So for the benefit of all of us let’s not leave one stone unturned
 
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In the opinion of the experts that I follow (Haakonsen and Landes, but mostly Haakonsen), cryo is unnecessary or “overkill“. Unless they changed opinion in the last year or so, I mean. Sub zero temperature (-75C/-85C) is meant to transform RA into Martensite and that’s it. According to Haakonsen, nothing was proved that going under those temperatures benefits steels somehow. Can’t remember if Larrin Larrin arrived to some different conclusions regarding sub zero vs cryo temperature tempering. Even Landes recommends -80C in his Cpm3v Heat Treatment recipe (but he also says “or lower”...).

Here https://edgematters.uk/thread/9605-heat-treatment-discussion/?postID=124167&highlight=Cryogenic+treatment#post124167 we can read Fredrik Haakonsen opinion regarding cryogenic treatment (His Nick name is Metallurgen).
 
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It's ETA Carbides not EDT

"η" = "eta" Greek letter
It is used to describe
Fe2c, a transitional iron carbide.


It is known thanks to folks like Larrin that there is no precipitation during cryo.
Although you can precipitate more transition carbides from a structure that has less retained austenite.

Also those eta carbides don't boost the wear resistance. Too small.

Getting more hardness out of the Cryo vs Sub Zero depends on the Austenitizing temp and what steel is used. If you run Austenizing temperture curves AQ with Cryo vs Sub zero you will see there can be separation as the temperature goes up with Cryo getting the blade harder on some steels.

You can put more alloy in solution and get more hardeness with cryo since it will convert better with the colder temp.

The idea with cryo is to improve the edge performance, better yield strength at the same hardness, the edge deburrs better and promotes more edge stability.

There is always some RA that is not converted and stays stable so going as cold as possible helps mitigate that issue better. Helps rule things out.

JTknives said:
So I have been wondering if cryo is all it’s cracked up to be. And by cryo I mean -320 Liquid nitrogen. The reason I am starting to question is because of what I have seen in steels response to it and subZ as well as all the heat treat data and research. Out of all the heat treating data sheets I have seen and looked at I can’t think of a single one that says to use cryo. Tons of them say freeze or subZ aka -100°f but not a peep of -320. What I have always heard around the forums is a long cryo soak precipitates EDT carbides. But from my research this is false as EDT carbides are formed during the temper cycle.

According to one paper I read thy stated that carbides actually grow larger as the temper temp goes up. So now that has me wondering if what we thought we where gaining with a cryo treatment and low temper is just the benefits of converting retained austenite and then bringing out the EDT carbides with the low 300-500° temper. I have heard that cryo increases hardness but honestly I have not seen a hardness difference on the testing I have done with cryo vs subZ. To me hardness is a multi factor variable that’s mostly affected by retained austenite. If that’s being converted over at the subZ then what is cryo doing for the steel after that?

I know this might be a little out there but I just feel that there is a lack of data to support claims that cryo does what people say it does. Just remember back in the day I remember when edge packing was the topic of conversation. So for the benefit of all of us let’s not leave one stone unturned
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Steels like v4e and z-wear need about -130f at the temps and hardnesses we like. Cryo is not needed, but sub zero isn’t quite enough. If there was another economical way to get to -130, we would be all over it.

We could use sub zero, but we would have to go a bit lower hardness to minimize retained austenite.
 
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JTknives said:
So I have been wondering if cryo is all it’s cracked up to be. And by cryo I mean -320 Liquid nitrogen. The reason I am starting to question is because of what I have seen in steels response to it and subZ as well as all the heat treat data and research. Out of all the heat treating data sheets I have seen and looked at I can’t think of a single one that says to use cryo. Tons of them say freeze or subZ aka -100°f but not a peep of -320. What I have always heard around the forums is a long cryo soak precipitates EDT carbides. But from my research this is false as EDT carbides are formed during the temper cycle.

According to one paper I read thy stated that carbides actually grow larger as the temper temp goes up. So now that has me wondering if what we thought we where gaining with a cryo treatment and low temper is just the benefits of converting retained austenite and then bringing out the EDT carbides with the low 300-500° temper. I have heard that cryo increases hardness but honestly I have not seen a hardness difference on the testing I have done with cryo vs subZ. To me hardness is a multi factor variable that’s mostly affected by retained austenite. If that’s being converted over at the subZ then what is cryo doing for the steel after that?

I know this might be a little out there but I just feel that there is a lack of data to support claims that cryo does what people say it does. Just remember back in the day I remember when edge packing was the topic of conversation. So for the benefit of all of us let’s not leave one stone unturned
Click to expand...

As to your second question, preventing the precipitation to larger carbides is the whole point to cryo/low temper. This results in better toughness, and when chromium is present, better corrosion resistance by keeping the chromium in solution.
 
Show me a double blinded randomized trial where one group of knife users get knives that have gotten cryo/LN2 and one group gets identical knives except they had normal zub-zero treatment at -100 something. And why not include a control croup with knives that had neither. Then measure user-experienced performance of those knives and compare for significant differences between the groups. After that the discussion becomes more interesting :)
 
Scaniaman said:
Show me a double blinded randomized trial where one group of knife users get knives that have gotten cryo/LN2 and one group gets identical knives except they had normal zub-zero treatment at -100 something. And why not include a control croup with knives that had neither. Then measure user-experienced performance of those knives and compare for significant differences between the groups. After that the discussion becomes more interesting :)
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Too subjective.
 
Scaniaman said:
Show me a double blinded randomized trial where one group of knife users get knives that have gotten cryo/LN2 and one group gets identical knives except they had normal zub-zero treatment at -100 something. And why not include a control croup with knives that had neither. Then measure user-experienced performance of those knives and compare for significant differences between the groups. After that the discussion becomes more interesting :)
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There are differences between testing material properties and comparing user experience. For example, you wouldn’t ask a group of office workers if they can tell that the new building has higher strength steel in it. And if you had a 10% improvement in edge retention with some new steel or heat treatment the best way of finding an improvement would not be handing knives to 100 people and asking them to cut things.
 
Well, you'll have figure out what the standard of deviation is first that users will get with the same knives, with the same HT, blind test without them knowing they are different.
Might be difficult without a way to quantify that.
So, you'll have to figure out how to measure "user experience performance" into something quantifiable so you can have measurable differences.

God Speed.


Scaniaman said:
Show me a double blinded randomized trial where one group of knife users get knives that have gotten cryo/LN2 and one group gets identical knives except they had normal zub-zero treatment at -100 something. And why not include a control croup with knives that had neither. Then measure user-experienced performance of those knives and compare for significant differences between the groups. After that the discussion becomes more interesting :)
Click to expand...
 
Scaniaman said:
Show me a double blinded randomized trial where one group of knife users get knives that have gotten cryo/LN2 and one group gets identical knives except they had normal zub-zero treatment at -100 something. And why not include a control croup with knives that had neither. Then measure user-experienced performance of those knives and compare for significant differences between the groups. After that the discussion becomes more interesting :)
Click to expand...

Or we could just use industry standard testing like a CATRA machine.
 
Drew Riley said:
Or we could just use industry standard testing like a CATRA machine.
Click to expand...

All good science require controlling and or limiting variables. Subjective experience is one of the lowest levels of evidence there is. It is useful in forming a hypothesis to test though, which fuelled my heat treat obsession seven years ago.
 
I just skimmed over Larrin's three articles again.
Very clear and thorough explanations.
I think that once anyone digests that info, they can then decide whether dry ice goes far enough for them, or if LN is preferred.
Given the facts, the rest is up to the individual.
 
I wish there was a chart that listed most of the knife steels we use and the martensite finish temperature for each. I've seen a few equations, but they usually don't compute correctly, and they don't even account for austenitizing temp. Correct me if I am wrong, we talk about martensite finish (Mf) temp, but as I understand, it really should be called M90, so that at "x" temperature 90% of the RA will be converted. Going colder will convert 90% of the previous 10%, and going even colder will convert 90% of that previous 10%, and so on down. If you were to graph the equation, the curve would always get closer to the axis, but never touch it. In application, cold treatments will never convert fully 100% of RA. And how much % RA is "necessary" is a big can of worms. The way I see it, at least go as cold as you possibly can to where you no longer see an increase in hardness, at least that.
 
Sometimes it's not just preference though there can be limitations due to processing.

Let's say you send out a batch of 10 knives, same steel to your favorite heat treater. Let's say they are all austenized together and individually plate quenched and checked for warping and fixing warps. That time between quenched to room temp and cold treatment is allowing RA to stablize. Especially if the heat treater decides to do cold treatment in a couple of hours.

Time to cold treatment is an important factor as Larrin's article points out and also that LN cryo can still convert some of that RA that stabilized while in limbo between quench and cold treatment that Dry Ice slurry cannot.

There can also be more error in DI slurry since it has to be made. Some folks don't add enough Dry Ice or Alcohol and also don't allow it the time to boil down to the coldest temp.
If the DI slurry is still boiling like when it's first mixed it's not at temp. You can also not add enough Dry Ice and it won't be cold enough.

Some folks don't always check the temp of their slurry to confirm, they just expect it to be "-130F"

I'll say that if you're sending out for HT you can't guarantee the time between AQ at room temp to cold treatment especially if it is a very large batch of knives. So, a LN Cryo does help rule out more RA.

Richard338 said:
I just skimmed over Larrin's three articles again.
Very clear and thorough explanations.
I think that once anyone digests that info, they can then decide whether dry ice goes far enough for them, or if LN is preferred.
Given the facts, the rest is up to the individual.
Click to expand...
 
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samuraistuart said:
I wish there was a chart that listed most of the knife steels we use and the martensite finish temperature for each. I've seen a few equations, but they usually don't compute correctly, and they don't even account for austenitizing temp. Correct me if I am wrong, we talk about martensite finish (Mf) temp, but as I understand, it really should be called M90, so that at "x" temperature 90% of the RA will be converted. Going colder will convert 90% of the previous 10%, and going even colder will convert 90% of that previous 10%, and so on down. If you were to graph the equation, the curve would always get closer to the axis, but never touch it. In application, cold treatments will never convert fully 100% of RA. And how much % RA is "necessary" is a big can of worms. The way I see it, at least go as cold as you possibly can to where you no longer see an increase in hardness, at least that.
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It’s not possible to give a single value for Mf or even M90 or Ms as with knife steels the values change depending on austenitizing. The temperatures can be estimated with various models, of course, but experiments would be more useful. There are very few studies where they actually measure martensite formation below room temperature. And to top that off the “martensite finish” temperature experimentally measured will be where the martensite formation stopped, but that does not mean that there wasn’t some RA too stable to transform. Generating austenitize vs hardness curves probably provides the most relevant information despite never measuring the actual martensite formation. That way you can see where too much RA is present, dropping the hardness. The amount of RA at peak hardness is typically 15-20%.
 
DeadboxHero said:
It's ETA Carbides not EDT

"η" = "eta" Greek letter
It is used to describe
Fe2c, a transitional iron carbide.


It is known thanks to folks like Larrin that there is no precipitation during cryo.
Although you can precipitate more transition carbides from a structure that has less retained austenite.

Also those eta carbides don't boost the wear resistance. Too small.

Getting more hardness out of the Cryo vs Sub Zero depends on the Austenitizing temp and what steel is used. If you run Austenizing temperture curves AQ with Cryo vs Sub zero you will see there can be separation as the temperature goes up with Cryo getting the blade harder on some steels.

You can put more alloy in solution and get more hardeness with cryo since it will convert better with the colder temp.

The idea with cryo is to improve the edge performance, better yield strength at the same hardness, the edge deburrs better and promotes more edge stability.

There is always some RA that is not converted and stays stable so going as cold as possible helps mitigate that issue better. Helps rule things out.
Click to expand...

that’s all things I have heard posted and talked about but what I’m wondering about is actual verifiable proof cryo does what is being said it does. Don't get me wrong I’m not saying it’s un true I’m just I’m just wondering about actual hard data.
 
We have an advantage now in that we go straight from the plates to the subZ freezer. Thy sit over night and are pulled out in the morning. I know some steels are quite sensitive to delays in cold treatments. Off the top of my head I believe A2 is one of those. We still keep LN on hand at all times but really loving this freezer.
 
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