Cryo Steel ?

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I have noticed some knives come with cryo steel, I assume this is a treating process to temper the steel. but I have heard people say this is not good. So why is this not good and exactly what is it and its purpose.
 
cryo, ice tempered, and all of those sayings are referring to the "heat treating" methods used. Doing a cycle in liquid nitrogen converts more of the retained austentite to martensite (that's the good stuff we want!), gaining a point or 2 in hardness and I think relieving a bit of stress as well. Wayne Goddard did tests with identically ground pairs of knives made in different steels, and all showed improved performance on rope cutting (edge retention) with the cryo-treadted blades. Keep in mind that cryo treatments are things you do in addition to tempering cycles using heat, not in replacement of.
 
Just a guess, but I'd bet the people who say it isn't good, don't have the equiptment to do it, or don't sent their knives to someone who does for heat treat.;)
 
Paul Bos does it on every blade he heat treats I believe; its part of the process. Id like to know who is saying its not good. Theres an old Norse ( I beleive ) saying, that " a blade left in the ice and snow over the winter season will cut very well"
-- Charles
 
I believe Spyderco use liquid Nitrogen, I think it's a fairly common process, they just don't make a song and dance over it in their advertising like some others do.
 
Cryogenic treatment of steel has been well documented for many years.

The confusion and controversy with performance gained is from how the cryo is applied.



Regards,
FK
 
Cryogenic treatment of steel has been well documented for many years.

The confusion and controversy with performance gained is from how the cryo is applied.

The temperature change must be gradual to the lowest, held for a fairly long period of time and gradual to ambient.

1. Dry ice and acetone-- this is popular with home hobby or small knife makers. Temperature is -108F, this is the least effective, dunk and remove,,,,not much time at the low temp. It is also a thremal shock to the steel.

2. Liquid Nitrogen-- many manufacturing companies use this method in combination with a heavy wall presurized and insulated vessel for heat treatment of high carbon alloys. Most processes dunk the steel into the liquid nitrogen or introduce the nitrogen to room temp parts, this is a severe shock to the metal grain structure. This liquid nitrogen was developed for the retained austenite to martensite transformation. This is why you will hear discussion of "if the initial heat treatment was done properly,,,you do not need cryo".

3. The newest and best is -300F with special equipment. Many readers of BF do not believe the claims of the metallurgy improvements by the commercial vendors of this service. The use of -300F is very well accepted for military aircraft components, expensive racing car engine parts, the most accurate rifle barrels, musical instruments and of course cutting tools. It is not hype to sell the service, this treatment does work very well as claimed. This process is done over a 24 to 48 hour time frame,,,,slow temperature drop,,hold at -300F,,,then gradual return to ambient.

Do a search for "cryogenic heat treatment"& "dry ice acetone" very interesting reading.

http://dmoz.org/Science/Technology/Cryotechnology/Cryogenic_Processing_of_Materials/

The gain for knife blades I believe, is the the precipitation of newly formed carbides arising from the sub-zero treatment process. It is well documented that tool steels used for machine tools have increased wear resistance and longer usefull life.

Regards,
FK
 
There is not really a "good" or "bad" about a way of heat treatment. No one can really say water quench is better then oil quench, or vaccuum quench is worse than air quench, etc. All we can ask of is only whether a heat treatment is good for the kind of steel we are looking at. In other words, it is the steel itself to decide what kind of heat treatment it ultimately requires.

I try not to be too malicious, but I wish to express my suspicion on some of the so called "high tech", "state of the art" means of heat treatment... are they really necessities? Is there really enough doubt on the heat dissipation rate for us to use liq. Nitrogen instead of water? (Note, it is a small thin piece of steel we call "a knife" in question!) Can liquid Nitrogen really "retain more austenite" than water does (by the way, they mean skewed austenitic lattice, that is martensite.) ? Don't forget the solid diffusion rate of steel is crap enough anyway, we simply don't need that kind of cooling rate to retain the whole lots of austenite in a knife.

I notice there are commercials about performance of "cryo" knives. I shall raise my example of "CS"'s video (no, they don't make cryo knife, it is just an example), people in the tape perform all kinds of amazing trick with their knives, sometimes it really make one to believe they are the only one who can do it, and their products do perform ahead of others in the market. However, we must remember it is the big man in the video who is chopping a block of concrete, not the knife itself. It is the big man in the video who slashes 8 ropes in one go, not the knife itself! When we are naming "tests", these results actually belong to the performers themselves, not the knife.

There are also commercials about military, aerospace, racing car components with their exquisite means of heat treatment. However, these are not knives! We don't need a transmission shaft in a F1 racer to "hold an edge", nor do we need a knife with a 2000+ MPa Young's modulus. These are different stories, nor would these materials be suitable for a knife (they won't hold an edge, nor have enough carbon to give a 60+ HRC of hardness). If they do, all knife we kave in the market would all be made of "Martensitic Aging Steel" (Maraging Steel) only.

I am not trying (in fact I am trying not!) to say cryo is bad. My point is, I believe it is more of a commercial measure, rather than of any realistic purpose for the performances.
 
Cryo treatment has most effect on medium and high alloy blades with complex compositions and tempermental heat treat requirements (air hardening steels, for example). With low alloy steels, expertly heat treated, the benefit is much less dramatic. Some might even say insignificant.

I don't recall anyone ever saying that it could be detrimental though.
 
CS does have some blades that are 440A sub-zero quenched... and there had been reports in here that says that they still don't hold an edge well.
 
Jin :

Can liquid Nitrogen really "retain more austenite" than water does
Click to expand...

The quenching medium doesn't soak up the austenite from the steel leaving martensite. As the temperature drops the austenite is converted to martensite. The amount of this conversion is smoothly dependent on temperature, you can find such curves in most materials works. This conversion doesn't stop at room temperature for most steels and thus bringing the steel to lower temperatures induces a higher percentage transformation, or lower retained austenite.

Besides this goal, which can infact be achieved by more standard methods such as multiple tempering, deep cryogenics (liquid nitrogen) also decomposes the martensite formed while conventional cold treatments (dry ice) do not. Deep cryogenics also effects subtle properties of the resulting martensite structure such as the types of carbides formed, specifically in promoting the formation of the high wear resistance eta carbides. This has all been well documented in various journals. Nu-Bit for example has shown the increase in lifetime of M42 band-saw blades, more than 50%.

-Cliff
 
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