Cryo tempering

It's cryo treatment . It can't be done after the blade is already heat treated .Check the yellow pages for heat treating companies.
 
Its called both. I think Texas knifemaker supply offers it and they call it 'deep cryo tempering'. You can do it after the heat treatment. In fact the benefits of this go along with the same principle that most of the benefit of H/T are in the cooling down or quench stage of it so this falls right in place with that.

I suggest reading some of the info here. http://www.onecryo.com/ and doing a google search. You'll find lots on it.

The benefits of the cryo treatements are beneficial to most all alloys. Some guys do it to their titanium and aluminum as well as their blades. It makes the steel harder and more durable and rids it of the larger unstable carbides as the temp. get closer to absolute zero. Get the treatment that takes it to -305F. Everyone says that is the best one. Some only go to -185F.

Some guys do their own with dry ice that will only get to -109.3F. I've read that this is somewhat controversial as to whether it helps as much doing this 'shallow' cryo treatment. I think it depends on when you do it, meaning it should be done while the blade is still in the cool down process from H/T. If it makes you feel better I'd say do it but its this shallow treatment that can't be done after H/T. Thats what I understood when we were talking about it in another forum anyway..

STR
 
It does NOT rid the steel of large unstable carbides .Carbides are very stable . It will only reduce the amount of retained austenite. The steel must be tempered after cryo. Do a search on this forum, there's lots of info.
 
Excuse me but 'retained austenite' is large unstable particles of carbon carbides right? Read the info in the link I provided. Thats where I got it from. If that is incorrect please explain how and why. My understanding of that is that cryo tempering does in fact reduce them further by converting the retained autenite into the much more durable martensite. Perhaps 'rid' is the wrong word to use. I should have said convert. I may have missed putting particles of carbon in there but thats what I meant. Correct me if I'm wrong though please. I thought I understood what I read and how this tempering process works..

STR
 
Austenite in steel is a crystal structure of iron with dissolved alloying elements including carbon . We then quench to produce martensite which is a different crystal structure also containing carbon. This is not a stable structure and we must temper.We then temper which takes some of the carbon out as carbides. In the higher alloyed steels we also end up with some retained austenite.We can reduce some of this by cryo treatment.That converts some of that retained austenite to martensite which then must be tempered. As we temper steel at higher and higher temperatures more and more carbides are precipitated from the martensite , lowering hardness and strength.
 
Are you saying that after Cryo treatment you still have to temper (re heat)? I want to understand this so I am sure to be passing on correct info. I've heard two sides to this. I realize there are two sides to this or rather that re heat is not being done a lot of the time.

Also, suppose a person did a shallow cryo of their own with dry ice is reheat necessary then in your opinion as well?

This info is from a book I have from a web site I found a while back on the basics of cryogenic tempering.

Austenite to martensite conversion - Normal hardening transforms austenite, with its unstable crystalline structure, into martensite, which is much stronger and more durable. But normal hardening doesn’t convert all of a steel’s austenite to martensite. For that to occur, cooling technology is required. Cryogenic processing results in a nearly complete transformation of retained austenite to martensite.

Carbide particle formation - Normal hardening creates carbide deposits that disturb the alloy’s crystalline structure. During the cryogenic phase of thermal processing, small carbide particles precipitate out of the crystalline lattice and are evenly distributed throughout the material. This reduces residual stresses and creates a very hard, fine carbide lattice structure with improved wear resistance.

Grain structure is refined - All of the individual particles that make up an alloy are placed into their most stable state. These particles then are aligned optimally with surrounding particles. Also, molecular bonds are strengthened by the process.

Internal stress is relieved - Particle alignment and grain refinement combine to relieve internal stresses, which can contribute to part failure. This results in material that is optimized for durability.

The extreme cold temperatures during cryogenic processing also slow movement at the atomic level, increasing internal molecular bonding energy and promoting a pure structural balance throughout the material. The end result is a material with an extremely uniform, refined and dense microstructure with vastly improved properties.



Being a metallurgist I would like to know if this is marketing hype or truth from you.

I thought that CT was suppose to reduce the size of the 'lumps of coal' carbides as they are called and also convert them to more useful durable martensite carbides to replace the austenite retained during H/T.

Thanks.


Steve
 
ASM International (the metallurgists' professional society) prefers the term "cryogenic processing" or "cryogenic treatment". Cryogenic tempering was coined by a promoter. The process is not a tempering process.

In most cases steels need to be tempered after cryo treatment because the retained austenite that is converted is converted to primary martensite which is brittle. Brittle is usually not good. It is rare that all retained austenite is converted.

Martensite is not a carbide. A carbide is a molecule of a metal and carbon. Metals are crystalline in structure, not molecular. Martensite is a body centered cubic crystal structure and austenite is face centered cubic. Therefore the change from austenite to martesite is one of how the ferric atoms relate to eacn other. There are more places for the carbon atoms to go in the austenitic face centered structure, so when the conversion happens, some carbon atoms precipitate out. Some of those link up with metallic elements such as chrome, vanadium, and even iron to create a carbide molecule.

Regarding shallow cryogenics, better known as cold treating (The Cryogenic Society of America defines cryogenic temperatures as those below -244F), it's main benefit is conversion of retained austenite. You will not get the other benefits of cryo treatment at those high temperatures. By the way theconversion of retained austenite only accounts for a fraction of the benefits of cryo processing. The conversion of retained austenite is pretty much finished at -140F. I have seen studies where cryo processed parts get considerable life increase even though tested against cold treated parts. In both cases, the percentage of retained austenite as determined by x-ray diffraction was about the same.

Regards to all,
Rick
 
Warbird , I welcome another metallurgist.In the 'old days ' we didn't get very cold , more like -100 F and called it 'sub-zero quench'. I've heard lots of claims about cryo but until someone can show me exactly why things will improve I'll stick to the retained austenite question....Last time I did some reading about carbides it was confusing some are metallic bonds , some molecular and some both IIRC !!
 
There is a really good article on cryo treating and it's advantages in the current issue of knives illustrated magazine. A2 is supposed to be the most effected with cryo causing edge retention to go up as much as 520% (if I am remembering correctly) D2 100% and some others. Something about carbides aligning themselves more perfectly in the iron matrix as the atomic activity slows down at the super low temperatures.
 
Well looks like I understated the improvement... A2 560% increase in wear resistance and D2 290% increase...sounds like it would be well worth it for these two steels. Kinda makes BRKT look good since they use A2 and do Cryo. A2 without cryo is pretty good.
 
I don't know of many that will be doing the cryo as described in the article, as it's not just immersion in LN2, but a very slow ramp down and hold, etc...
It does look like a good improvment over simple immersion, and the prices to have it done are reasonable at the places listed in the article.
Now, if the heat-treaters would also be able to offer this type service at the same time, it would be a plus.
 
The claims have been made that nonferrous metals such as brass also benefit so obviously carbides can't be involved . So then what is the mechanism ?
 
Just for info, I regularly send machine cutting tools (end mills, ect) to One Cryo, and we have noticed an increase of tool life exceeding 200%.

These cutting tools are already heat treated and ready to use as is. One Cryo does not temper them after cryo treatment.
 
Interesting! It has been written many times that only high chrome steels benefit from cyro. This has been basically the way thing have been in the knife industry for many years. I don't know how many times I have read in the publications that simple steels, such as A-2 , 0-1, will not benefit. What gives? Mike
 
mete - My assumption is that at the deep cryo temps (-250) the atomic movement slows to a point that the bonds are able to align and attach better.Upon return to normal temp,the alignment holds,due to the more orderly arrangement.
For the layman - if you have a room full of pre-schoolers (iron,chrome,,carbon,etc) and you want them to gather in a line,it will be a very disarrayed assembly,due to the fact that they never stand still long enough to get in order.Slow them down (deep cryo) and get them to notice where the other kids are (crystalline structure) and they will form a much neater line.Once in line they only have to pay attention to the kids directly next to them (bonding) for the neat arrangement to stay tight.When the line starts moving (warms up) the order is defined and remains the same (harder and more wear resistant).
Stacy
 
Baseball great Ted William's head and body (in separate containers) are in a cryogenic container in nearby Scottsdale. I wonder if Ted has been imbued with more wear resistence or toughness? :p
 
bladsmth said:
mete - My assumption is that at the deep cryo temps (-250) the atomic movement slows to a point that the bonds are able to align and attach better.Upon return to normal temp,the alignment hold,due to the more orderly arrangement.
For the layman - if you have a room full of pre-schoolers (iron,chrome,,carbon,etc) and you want them to gather in a line,it will be a very disarrayed assembly,due to the fact that they never stand still long enough to get in order.Slow them down (deep cryo) and get them to notice where the other kids are (crystalline structure) and they will form a much neater line.Once in line they only have to pay attention to the kids directly next to them (bonding) for the neat arrangement to stay tight.When the line starts moving (warms up) the order is defined and remains the same (harder and more wear resistant).
Stacy
Click to expand...

Excellent example for explanation....I was trying to come up with something nice and easy like that to explain, but wasn't getting anywhere...I am sure that pretty soom Cliff (Stamp) will show up and post the five page technical explanation for those that want it. I have a friend that is working on his PHD in Metalurgy.....I will ask him next time I see him and post his explanation here.
 
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