5 Things You Should Know About Cryogenic Knife Treatment
You’ve probably seen the term thrown around forums and knife product descriptions. Cryogenic treating, or processing, or refining, or whatever a knife manufacturer decides to call it, sounds suspiciously like marketing nonsense.
Blade Mag covered this topic pretty well by interviewing some high profile knife makers like Paul Bos and Bob Bealy. The process is explained along with the benefits but they kind of rush through whether it’s worth a knife buyer’s money, leaving it at “a cryogenically treated blade could make the difference in performance and easily justify any minimal added expense”.
This still left me with a few questions, though, like “how much of an added expense” and “how do I know a company is doing it well or just slapping the word ‘cryo’ on the steel to sell off the buzzword”.
SOG’s knife buying guide loosely describes how they do their cryo treatment and say the “process relieves the blade material on an atomic level” making it tougher and less likely to chip. That all sounds fine, but anytime I hear someone selling something as effective because it “works on an atomic level” I get suspicious.
So I tried to figure the thing out for myself. Here’s what I landed on after a couple of weeks of research just in case you don’t feel like reading through another thousand words of my stumbling through technical steel crafting processes I still only half understand:
- Yes, cryogenic treatment improves some types (high alloy) knife steels
- It does more for long term toughness than any kind of hardness or sharpness
- Probably every large knife manufacturer is doing it on some knives
- No, we probably aren’t paying extra for knives as a result.
What is Cryogenic Processing
The purpose, on a simplified technical level, is to convert austenite in the steel to martensite.
For most people that is not a very helpful sentence, so here’s a quick breakdown on stainless steel crystalline structures and why a knifemaker might want martensite over austenite.
The Four Stainless Steel Structures
- Martensitic: A hard structure built up around the composition of iron, chromium, and carbon. This structure can be heat treated.
- Austenitic: A face-centric cubic structure that can not be hardened by heat treatment. Generally results from the addition of nickel, manganese, and nitrogen. Tends to make steel more brittle.
- Ferritic: A body-centric structure resulting from high-chromium content. This is usually a very soft and corrosive resistant structure often used in cheaper kitchen cutlery.
- Duplex: A form of hybrid between austenitic and ferritic steels (it’s sometimes called austenitic-ferritic) that tends to be more corrosion resistant than the austenitic structure and harder than the ferritic structure.
That is a grossly generalized overview that’s probably making a few intelligent people cringe, but as we’ll see, there are other people who have explained it better.
As I understand the very in depth (but surprisingly readable) articles on cryogenic processing by the Knife Steel Nerds, alloy steels that are high in carbon and chromium tend to leave more austenite because the more elements you add to a steel the lower the temperature in which martensite forms will be. That’s likely a gross oversimplification, but for our purposes as consumers, it’s good enough for now.
What’s Actually Happening Inside the Steel
Most steels, when they’re first made, aren’t perfect, and the many machining processes they go through to become a knife or beam or hammer often add to those imperfections. Heat treatment is one of the ways those imperfections are fixed, but even after heat treatment, the steel can still be anywhere from 15-20% austenite, leaving it more brittle than the steel is capable of.
Thanks to the science magic properties of austenite and the (potentially) surrounding chemicals within the steel, the way to get that austenite to dissolve into more uniform martensite is to bring the steel down below freezing.
The process, as I understand it, is sort of like elements dissolving into each other. Baking always seems to make a healthy analogy to treating steel, so in this case, you could think of it like baking cookies hot enough to break the sugar down, causing the dough to flatten out, then freezing the cookies to where the sugar crystallizes and makes it sweeter.
So in a situation where you want your steel to become “sweeter” you need to heat it up to get things moving around, then cool it down carefully so those things can fix themselves into a better structure. Basically, it heats up the metal until the atoms are mobile enough to realign and become more symmetrical. The methods used to heat and cool the metal, along with the time spent on each stage determine whether they realign properly.
Is Cryogenic Processing Making Your Knife Better?
In theory, yes. But like everything with a complex craft, it depends on the materials and the application.
If done right, the process should make the steel tougher, but not all steel types react to the process in the same way. Some react “better”, or more dramatically, and others just don’t have the chemical make up for it to make much difference at all.
The simple way to look at it is steels with more chromium benefit more from the process. In particular, chromium’s presence alongside a lot of carbon gets the most mileage out of being frozen and thawed.
Paul Bos told Blade Magazine he cryo treats high alloy steels, and actually went into some surprising depth about his process. Over his career, he’s seen companies cryo treating everything from nylon stockings to gun barrels, and figured it could probably do a lot for knife steel but he clarified that “its effects are more profound in high alloy steel”.
D2 steel, in particular, seems to benefit a lot from the process, and I would go so far as to guess that it holds doubly true for cheaper Chinese steels like 8Cr13MoV (though admittedly I’m far from a heat treat expert, and most of my knowledge is from a decade-old article and a bunch of internet forums).
The truth is, though, that most of us probably won’t notice the difference. This is steel we’re talking about. Even soft steel is pretty damn hard, and most of us will never use our knives in a way that would make us notice the added toughness between regular steel and cryogenically treated steel.
That’s not to say it doesn’t add some life and value to our knives, just that you shouldn’t expect to see the improvement in any immediate sense like you would in a knife that just has a good heat treat and edge geometry in the first place. Those are the kinds of things that will keep a knife cutting paper after a round of ill-advised batoning. Cryogenic treatment is more about longevity than direct performance.
Is Cryogenic Treatment Worth the Money?
First off, how much is the cryogenic process even padding the bill?
Bob Beaty told Blade magazine that it doesn’t make knives that much more expensive.
In a perfect world, knife makers cryo treat their steel to get the most out of the steel properties. What’s far more likely is that companies cryo treat large batches of knives to compensate for heat treatments that inevitably suffer from mass production.
In that situation, the treatment probably isn’t affecting the price much if at all. Either the company is sending the blades off to a third party in bulk or doing it themselves in large batches on site. The reason the consumer doesn’t feel the additional labor is the same reason the knife ends up affordable in the first place: the wonders of mass production.
We might feel it more from custom knife makers: The guy who makes one to ten knives to order and wants to squeeze as much utility out of the steel after his heat treat. So he either invests in some kind of nitrofreezer to do it himself or sends it to another company to do it
That knife maker will feel the extra steps in his bottom line a lot more than Benchmade or Cold Steel, but if he actually knows what he’s doing whatever small bump in price reflects a knife with steel that has been made about as tough as it’s possible for it to be.
Who is Cryo-Treating their Knife Steel
It’s tricky to find out exactly who does cryogenic treating and what they’re doing it to, because most companies don’t go into that much detail about their treatment process. SOG clearly does it on at least some of their knives since they explain the process in their buyer’s guide. Rumor has it Benchmade uses some kind of cryo process, and Spartan Blades touts their “double deep cryo heat treatment” in most of the product descriptions of their Gold Grade knives.
The real answer, though, is probably everyone. It seems to be well enough established as an effective method for improving certain kinds of steel. If you look at cryogenic processing plants you see they have clients across a huge range of industries including aviation and tooling. Most of us are probably commuting or drilling holes with cryo treated steel every day.
If cryo treating is nothing more than a marketing ploy, then it has an enormously wide spread placebo effect. What seems far more likely is that it’s used as a marketing ploy by companies with slipshod heat treatments, while everyone else just does it on their high carbon steels as a regular matter of course, and they expect us to trust them enough to know what they’re doing without explaining every damn step of the process.