Talk to me about no cryo heat treat.

Cypress Creek Knives

Cypress Creek Knives

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Recently I have spoken to a few makers who are heat treating stainless steels without a cryo treatment and with a low temperature temper. I know this heat treat will leave more RA in the steel compared to a high temp temper or a cryo treatment. My question is how much will this affect steel performance? I know that skipping a cryo treatment will leave some performance on the table, but would it be noticeable to the average user?

I'm not necessarily looking to skip the cryo step, but I am curious about real world experience with a no cryo low temper heat treat.
 
my experience tells me that geometry makes a bigger difference than a point of hardness. I wouldn't balk at buying a knife that wasn't cryo quenched if I knew the maker understands what the knife they made is meant to do, and ground it accordingly. Or an artsy knife, in which case I wouldn't care at all.

I personally like to geek out a bit with heat treating, but I think sometimes people get a little too caught up in the minutae and don't pay enough attention to the other important things that make a knife pleasant to use. Seems to me like many people wouldn't notice the difference until it came time to sharpen their knife. Maybe also wrt stainlessness.

if I wasn't using liquid nitrogen for quenching, I'd likely opt for the high temperature temper for those alloys where it's an option.

I'm still a neophyte, so if I'm wrong about any of that I don't mind being corrected!
 
DevinT said:
If you’re making custom knives, give the customer the best possible heat treatment.

If you don’t, you won’t sleep as well at night.

Hoss
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That is an excellent point, and I share that sentiment.

Just for my education, it is my understanding that there is no real difference between toughness and RA when comparing no cryo/high temper and cryo/low temper heat treat protocols. If this is the case what real benefit comes from cryo? Better corrosion resistance in stainless steels? And if one was to use a no cryo/low temper protocol, how much performance is left on the table? It seems to me that there would be more RA in the steel which would result in a tougher blade, and you would get a point or two reduction in max hardness, which could be negated by the tempering temperature. If this is the case (I may be totally incorrect in these assumptions), why is cryo such an important step?
 
Cryo increases as quenched strength (hardness).

Cryo eliminates most RA improving long term stability. RA can convert to fresh martensite under certain hard use conditions.

Blades that have been cryo’d , are easier to sharpen due to easier burr removal.

Hardness is the main indicator of edge holding for a particular alloy.

There is a bigger story you tell the customer when you use cryo.

It’s a good practice.

Hoss
 
Fieldknives said:
Excellent article about this: https://knifesteelnerds.com/2022/01/11/how-cold-for-cryo/
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Thanks for the link! I have read that article a couple of times before, and read it again this morning. I also read the 3 articles Larrin linked as well.

This quote is from the FAQ section in the article you shared

"Which steels “need” cryo?
With virtually any steel, as long as you are using an austenitizing temperature at peak hardness or below, the steel is going to be fine. Beyond that there is excess retained austenite which reduces strength. This limits the hardness for some steels more than others. LC200N and Vanax, for example, top out around 60-61 Rceven with cryo, and a couple points less without it. Higher hardness is possible with cryo, of course, and in some cases you get an increase in hardness with little change in toughness as pointed out in the studies above."
And this quote is from this article https://knifesteelnerds.com/2018/12/10/cryogenic-processing-of-steel-part-2/

"This means that in general, a lower tempering temperature is required to achieve the same hardness level with secondary hardening. Using the same tempering temperature as without a subzero treatment will lead to a greater degree of tempering. More tempering can be good or bad depending on the situation. Excessive tempering can lead to coarsening of tempering carbides which can reduce toughness. However, if the tempering was insufficient without subzero, the use of subzero processing may increase toughness due to shifting the “optimal toughness” range."

With this being said, if I were going to temper a steel such as AEB-L to 62rc, is cryo really necessary? I know there would be more RA in the steel, but is that really detrimental to its ultimate performance, or are we just splitting hairs at this point?

I guess I'm trying to ask how significant of a role does cryo really play? It seems to me, based on what I've read, that cryo is a beneficial step but doesn't have a massive increase in performance (unless one is trying to reach maximum hardness in a steel).
 
DevinT said:
Cryo increases as quenched strength (hardness).

Cryo eliminates most RA improving long term stability. RA can convert to fresh martensite under certain hard use conditions.

Blades that have been cryo’d , are easier to sharpen due to easier burr removal.

Hardness is the main indicator of edge holding for a particular alloy.

There is a bigger story you tell the customer when you use cryo.

It’s a good practice.

Hoss
Click to expand...
I was unaware that RA can convert to martensite under certain conditions. That is very interesting. Converting as much RA as possible via cryo treatment would reduce the chance for late stage martensite embrittlement then?

What factor does cryo play in burr removal? Thats very interesting as well.

A good story is always a big help in selling knives lol!
 
Cypress Creek Knives said:
I was unaware that RA can convert to martensite under certain conditions. That is very interesting. Converting as much RA as possible via cryo treatment would reduce the chance for late stage martensite embrittlement then?

What factor does cryo play in burr removal? Thats very interesting as well.

A good story is always a big help in selling knives lol!
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Burr removal stubbornness has to do with increased toughness at the edge because of the RA (which is unstable).

Hoss
 
RA is Retained Austenite. Austenite normally converts to martensite with continuous cooling. If it does not cool low enough some of the austenite does not convert. Other things can cause phase conversions. Added energy can cause a change from austenite to martensite. When using a knife it flexes (or tries to) and has impact on things if used for chopping. These additional forces can add enough energy to the grains to cause atomic plane shuffling (I think that is right?) and cause the transformation. The new martensite will most likely be where the most energy is added ... at the edge. So, now you have an edge that has some amount of untempered brittle martensite in it. This can create micro-chipping, and even possible a micro-crack forming. Additionally, there is a volume change with the conversion, creating tiny stresses in the edge. None of these is desirable in a knife blade.

Now, is this a large enough change to be a real worry - No. But it technically does lower the blades quality.
 
I’ve definitely noticed since adding in dry ice to the stainless alloys I work with that burr removal is easier and I’m getting a keener edge, I’m also running about a point or two harder than I was prior and with a high temper, I’ve not had any issues with edge stability or toughness and like Hoss mentioned gives me the peace of mind that I’m going through all the necessary steps in my heat treating. Before using cold treatment I’d typically adjust my Austenizing temp down and temper down to hit the hardness I want and minimize RA. I also agree with Lorien that edge geometry has a larger impact on overall performance but adding in a cold treatment is a really simple step to get the most out of the steels we use. (For a short period when I started using stainless I couldn’t source dry ice or LN without a commercial account but now I’ve been able to find dry ice regularly) (double side note most of my models won’t fit in a standard dewar so dry ice is much more practical)
 
one thing that sucks about using LN2, for me, is that it somewhat limits what I can make/design- for the reason Josh mentioned. Not only is the opening of my dewar about 2", the whole tube that protrudes into the vessel is the same diameter, so really wide knives won't fit and wideish knives with a curvy profile won't fit. I'll get a bigger dewar one of these days, but space constraints are a real issue for me currently
 
LN lasts for a while in a dewar, but it *does* evaporate… so is likely economical for folks that do larger quantities of knives, and not so much for the occasional hobbyist. Back in MN it was difficult for me to locate dry ice. Curiously, here in Louisville, *all* of the grocery stores carry it (which is also interesting to me for making sushi…).

(I also now have a very handy 240v outlet in my garage … so might seriously start thinking about doing my own HT…
 
Dry Ice can be found in most anywhere now days - welding supply places, grocery stores, marina bait shops, seafood markets, party supply stores, restaurant suppliers, medical supply stores, fire system companies, etc.

Just for fun I checked places in SE KY and found several. You may have to drive a bit if you are rural, but in most cities it is often less than 30 minutes.
 
Stacy E. Apelt - Bladesmith said:
RA is Retained Austenite. Austenite normally converts to martensite with continuous cooling. If it does not cool low enough some of the austenite does not convert. Other things can cause phase conversions. Added energy can cause a change from austenite to martensite. When using a knife it flexes (or tries to) and has impact on things if used for chopping. These additional forces can add enough energy to the grains to cause atomic plane shuffling (I think that is right?) and cause the transformation. The new martensite will most likely be where the most energy is added ... at the edge. So, now you have an edge that has some amount of untempered brittle martensite in it. This can create micro-chipping, and even possible a micro-crack forming. Additionally, there is a volume change with the conversion, creating tiny stresses in the edge. None of these is desirable in a knife blade.

Now, is this a large enough change to be a real worry - No. But it technically does lower the blades quality.
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Stacy, if the use of cryo doesn't have a "real world impact" (meaning it doesn't make a noticeable difference to the average user doing average tasks), why is there such an emphasis on this step? I understand that as makers we want to get the most performance out of our steel (I do use a cryo step and plan on continuing to do so), but is it really necessary? It seems to me that "good enough" comes into play here. All of these extra steps add cost and time to a blade, and at some point the benefit added won't exceed the cost and time increase. If this is the case, and the average user won't notice any difference, why are we so hyper focused on it? Does skipping cryo make a knife inferior to one that has been cryo treated, or are we just catering to the few who are steel snobs, like many of us here?

Joshua Fisher said:
I’ve definitely noticed since adding in dry ice to the stainless alloys I work with that burr removal is easier and I’m getting a keener edge, I’m also running about a point or two harder than I was prior and with a high temper, I’ve not had any issues with edge stability or toughness and like Hoss mentioned gives me the peace of mind that I’m going through all the necessary steps in my heat treating. Before using cold treatment I’d typically adjust my Austenizing temp down and temper down to hit the hardness I want and minimize RA. I also agree with Lorien that edge geometry has a larger impact on overall performance but adding in a cold treatment is a really simple step to get the most out of the steels we use. (For a short period when I started using stainless I couldn’t source dry ice or LN without a commercial account but now I’ve been able to find dry ice regularly) (double side note most of my models won’t fit in a standard dewar so dry ice is much more practical)
Click to expand...

I agree with you and Lorien that edge geometry plays a larger impact on performance than a cold step or not. I feel like there is appropriate focus on the edge geometry discussion, and perhaps too much focus on cold treatments. The discussion around cold treatments tends to suggest that a non cryo treated blade is an inferior product than a cryo treated knife. I'm not convinced that this is the case, hence my post on the subject. As a maker and user I'm more interested the real world difference. If I can make a non cryo blade with great performance and save my customers a chunk of change on each knife, it may be something to consider.
 
Lorien said:
one thing that sucks about using LN2, for me, is that it somewhat limits what I can make/design- for the reason Josh mentioned. Not only is the opening of my dewar about 2", the whole tube that protrudes into the vessel is the same diameter, so really wide knives won't fit and wideish knives with a curvy profile won't fit. I'll get a bigger dewar one of these days, but space constraints are a real issue for me currently
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Don't get me started on the 2" opening on dewars😂
 
Cypress Creek Knives said:
cryo step and plan on continuing to do so), but is it really necessary? It seems to me that "good enough" comes into play here. All of these extra steps add cost and time to a blade, and at some point the benefit added won't exceed the cost and time increase.
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lol. A few years ago I raised the “good enough” question here re potential benefits for @57-58 hardness blades for quick resharpening in the kitchen … and promptly got hammered by many folks. I think it’s a religious thing….

A few weeks ago I posted a comment where I was looking at a commercial kitchen knife, where they prominently advertised “cryogenic heat treating” … along with a hardness of …. 58. This makes no technical sense, but I guess the fancy words allow them to sell the things.

Then again, I have given several kitchen knives to friends … hardness about 62, and they refer to them as “the knives that never get dull” … so the hardness thing can be recognized by some people..
 
Cypress Creek Knives said:
If I can make a non cryo blade with great performance and save my customers a chunk of change on each knife, it may be something to consider.
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I recommend doing some side by side testing and see what works best for your product budget and target audience.

Make sure to document your testing well so you can revisit it in the future as you grow.
 
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