Cryo tempering

mete:
Thank you for the welcome. Retained austenite and the relief of residual stresses are all part of the results on some ferrous metals. But what about the double or triple the life consistently achieved on pearlitic cast iron brake rotors. I've analyzed rotors. If there is any austenite in them it is too little to detect. Perhaps carbide makes some difference, but then why does the process work on copper, aluminum (NASA Study) Bronze, etc.?

Howiesatwork:
You are very right, simple immersion it is not. Research from the Soviet Union shows that you have about a one in ten chance of making any improvement by immersing a part in LN2. Immersion or even spraying liquid nitrogen on a part can cause cracks and degredation of performance. Think of dropping a cannon ball into LN2. The outside wants to be -323F, and the inside remains at room temp for a while. The outside tries to shrink to the size it would be at -323F, creating tensile stress and possibly cracks. Also, by lowering the temperature slowly, you allow time for the reaction to take place before it gets too cold to happen. For instance, the number of vacancies in the crystal structure is temperature dependent. So as you drop the temperature, you force some vacancies out. But if you drop the temperature too fast, you can "freeze" them in. See "Structure-Property Relations in Nonferrous Metals" by Alan M. Russell, Wiley, 2005, Page 19.

mete:
bladsmith is on the right track. A lot of things happen as things get colder. The solubility of alloying elements in the matrix changes, which causes elements to redistribute. This is probably the mechanism for the formation of carbides. Also, Mark Eberhardt at the Colorado School of Mines has some theories regarding the metallic bond. In (very) short, there is an optimal distance between atoms in the crystal structure. A shorter distance or longer distance represent a higher amount of energy in the structure. Cooling brings the atoms closer together and allows them to "pop" into the ideal distance. This is theory, but has some support in the metallurgical world. Basically, you get a more ordered and more perfect crystal by cooling it slowly.

Code 3
Try it on carbide tools. Works just as well.

mlovett
A lot of stupid stuff has been written about cryogenic processing. I often hear that you cannot get any benefit in M2 steel. That's news to me. Others say you can't use it on cast iron, but racers and police consistently get three times the life on cast iron brake rotors, and we've been doing cast iron engine blocks for over twenty five years. Recently a police trade magazine came out and claimed you should not use cryo treated rotors with ceramic brake pads. Huh? I do it all the time. Unless you see research or have personal knowledge, it is hard to know what to believe.

gspam1
Ted Williams was a pretty tough competitor to begin with. ;)

I guess I'd better tell you fellows if you have not already guessed it. I work in the cryogenic processing industry. It really burns me to see people talk about "densifying" metals with cryogenics and other silly cryo tricks. The process is so good it does not need people to make up things. By the way, you can see a list of articles about cryogenic processing at http://www.cryogenicsociety.org/publications/cold_facts/current/cryogenic_processing_articles.php . This was done as a cooperative project between the ASM Cryogenic Processing Sub-Committee and the Cryogenic Society of America.

This is a great discussion, let's keep it going so we all can learn more.

Regards to all,
Rick
 
Warbird, Glad to have your voice and experience here. We need more people like you to help explain the metallurgy.
As an former research chemist,I agree with you that the PR and hype on things like "Mystery Quenchants" and "Cryo Tempering" does more to ruin a good thing than promote it.
I believe that cryo can be done far better than it is currently done in dewars of LN.Problem is that many makers want to do it themselves.Proper cryo is the realm of specialists.I find the more complex the steel,the more the advantage.The more I read on the subject,the more I realize how little some cryo treatments actually do.Onecryo's process seems to be on the right track.
Another illustration I have used is a marching band on the field at halftime. Things appear to be chaos, but by keeping close to the guy in front of you and forming neat rows with the guys on either side, the whole band works as a solid unit.No one instrument has any idea what the whole band looks or sounds like,just what the arrangement with its neighbors is.Proper placement of the brass, woodwinds,and percussion make it all a strong unit with good performance.A complex steel alloy behaves similarly.It takers time durring soak for the players (iron,carbon,chrome,etc.) to get aligned and start playing together.Stop the action too soon (not a long enough soak time) and the show is not up to what it could have been.
Stacy
 
Thanks for the info, Rick.
I don't think I can do a 1 - 2 °F ramp down in the chambers I have at work, even though they're designed to do -65 to 250°C on their own, getting to -300° takes a better insulation than what we have.
Vacuum jacket insulation, which we don't have...
We did a test for a customer once that was a 30 minute ramp from +100 to -125°C and back, while having the product powered up, doing 3-axis 2g random vibration.
Used massive amounts of LN2, though.
The test was successful, but their product needed re-engineering...
There's a company locally that does the type cryo-treating profile described in the article in K.I.
I'll have to get with them this week, and get some more info.
 
Stacy:
You sure have a way of coming up with good analogies. Yes, cryo can be done a lot better. Present practice is mostly developed by empirical knowledge. We need some interested professors to help develop theories and then test them. Once we can prove those theories, we can optimize the process. Most of them and most of us in the industry are so busy trying to justify the process that we cannot spend time or money to do the proper research. If you read the research, it is mainly done to show some sort of wear reduction, usually in a specific application area. While this is valuable, there are those among us that wish we could get on to the phase of research where we can find out why it works. My company has a standing offer to help researchers. Onecryo is on track, but there are places a lot closer to you that can do as well or better. Email me if you would like names and phone numbers.

howiesatwork
Proper machines make it much easier. We've done seven day tests on electronics at -300F. Our vacuum insulated machines use only about 7 liters/hour at that temperature, so we can economically treat things for long periods of time. Vacuum insulation has a lot of advantages besides economics also.

If you fellows know anyone interested in doing real research into the process, get a hold of me. As chairman of the ASM committee, I need to coordinate more information exchange and research.

Regards,
Rick
 
Based on the excellent information in this thread and the links provided, it does not appear that cryo is really an inhouse knifemaker's operation. I'm sure the companies mentioned in the Knives Illustrated article for example, wouldn't want to share their ramp down and soak times as that information is proprietary, but it sounds like an exacting process.

Could the slow cooling times be approximated in the small shop with simple equipment? As an off of the top of my head example, a protocol such as:

1. cool blade after quenching in refridgerator for an hour
2. put in home freezer for two hours
3. put in dry ice for 4 hours
4. lower into LN for 24 hours

Would there be any benefit to the steel in doing something like that? I'm guessing not, but would be happy to be corrected.

Is this a sophisticated equipment only process? I was getting close to buying a Dewars tank and start dipping blades, but it sounds like that would be a poor decision now.

George
 
I have what could be a stupid question regarding something I read in the K.I. article. It states that steels become much more wear resistant with the cryo protocol (in the case of A2 560% more wear resistant) then it goes on to state that sharpening is no more difficult since the blade is at the same hardness as before.....isn't this a contradiction in terms? How could a blade be 560% more wear resistant yet still be just as easy to sharpen? Sorry if this is a dumb question, but I might be misinterpreting what they are trying to say here. I am sure someone here with a bunch more experience than I have can shed some light on the subject.
 
Sharpening is a process of using an abrasive of higher hardness than the blade.Diamond,silicon carbide,etc. Wear is the process of a softer material causing frictional movement of the atoms on the edge,thus creating a dull blade. They are not the same. With Cryo the atoms are tighter and thus harder to move out of position by wear.The hardness is the same,so sharpening will be the same.The edge is made of tighter and stronger bonds and will resist dulling many times longer.
Stacy
 
gspam1:
The profile we would use for your blade is 9 hour ramp down from room temperature to -300F. Hold at -300f for 20 hours. 15 hour ramp up to room temperature. Temper twice with a ramp up to tempering temperature of 1 hour and a hold of 2 hours. Maybe a third temper. Tempering temperature depends on the steel. Other companies may vary this. The value of the hold time is the longer you hold, the more eta carbides are initiated. Most reputable cryo companies will have a similar cycle. A lot of the success of the process also has to do with the method of cooling. For instance, some companies use a spray of liquid nitrogen to cool the parts. We've seen this degrade performance if the part is near the spray bar. Our machines use a heat exchanger which cools the air which cools the part. We find this is a more gentle way of cooling. I believe the home method you describe would not be optimum and could cause problems. You would still be dipping the blade into LN2 and rapidly going through the temperature between approx -110F and -300F. There is good reason to believe that the part needs to be slowly cooled through that temperature range, but there is no proof of this.

Best results are being achieved by the use of good equipment. The thing that really made cryogenic processing practical was the invention of the microprocessor based controll units used on most machines.

bigbcustom
I agree with bladsmith on this. I would add that you will get a finer edge on a cryo treated blade because of the hardness being more even. I've done multiple hardness tests on parts, then treated them. The standard deviation of the hardness drops dramatically after cryo treatment. The more even hardness translates into better grinding conditions. For instance, I have a customer who makes tooling. He used to rough out the grinding with a coarse wheel and then finish with a fine wheel. After cryo, his surface finish was so good with the roughing wheel that he eliminated the grinding with the fine wheel.

Regards,
Rick
 
Rick,
Thanks for the information.
Seems I do have a chamber that will do it. An LN2 Dewar...
So now all I need is a heat exchanger, and a few other little things.
Off to designing and building a heat exchanger, unless the one from our old cryo-cooled diffusion pump will fit...
 
I've wrestled with jumping in on this or not for I have only cyro treated about 30 blades since I got my dewar last spring and forsure I'm no authority on the total plus or minus benefits. But when someone comes in and says it's not beneficial if not done by a commercial heat treater, I have to disagree. I quench and snap temper 1 hour before lowering my blades into the LN for a 12 hr. soak. Now from the physical tests I've performed on my blades they do show greater edge holding ability, more strength and more flexiblity. On no blades yet has it shown non beneficial for me and there's many others that do the same process that have found it to be very beneficial. Believe me if it didn't show beneficial in my shop, I wouldn't spend the time running down the LN, spend the money to buy it and lose the time needed to soak it.

Bill
 
Bill,
I don't think it was stated that an LN2 soak was not beneficial.
Just that taking it down to LN2 temperatures slowly was more beneficial.
 
Howie I'm not trying to start trouble, I just don't want anyone coming in here and reading this and then going away with the conclusion that if a blade isn't cyro treated by a commercial heat treater its a waste of time. Here's that statement I was addressing, that could lead people to believe my concerns.

"Based on the excellent information in this thread and the links provided, it does not appear that cryo is really an inhouse knifemaker's operation.

I spend to much time and money doing cyro treatments without adding extra for it, I only do it because it does prove very beneficial, and I do it in house.

I did not mean to disrupt your conversation, sorry, carry on.

Bill
 
Bill, You are not interrupting this conversation - you are a part of it. Everyone has their own opinions on this subject.Yours are backed up by experience.Cryo does improve a blades performance.This thread was aimed at how cryo can be improved,and what is being learned about how it works. In shop cryo is far superior than no cryo.The benefit is obvious.I agree that a new maker might construe that putting a blade in a dewar of LN would be useless.Not so.
Controlled process cryo,however, is beyond the reach of most small shop makers.The extra gained is just that - extra - above and beyond the gain from a LN dunk.What the industry is trying to find out is how much more you can gain.
Stacy
 
I have a couple of dumb questions to toss out.

What exactly is the container or machine that allows the slow cooling rate and how does it work? Is the nitrogen gaseous to a very low temp at which point it liquifies? So the large treaters have a container of some sort that is both air tight and liquid tight?

Is there an optimum amount of time for the quench?

Does it work for H1 metal? As I understand it H1 doesn't have carbons.
 
howiesatwork:
We use coiled aluminum tubing for a heat exchanger. Do not try to use a radiator, as frost will plug up the airways. (Been there, Done that).

B. Buxton
As with any process, proper equipment is needed to get optimum performance. I can heat treat with a torch and a bucket of water and temper with the torch, but I doubt that optimum results would result. I can carburize metal by packing it in bone and heating it, but if I want the best results I send it to a company that can vacuum carburize the material and do it well. If what you are doing gets you the results you are looking for, then go for it.

By the way, most commercial heat treaters know nothing about cryogenic processing. I am told one local heat treater rolls his eyes when ever it is mentioned. There are a few who do understand the process, but mostly what they call cryogenic processing is either -110F cold treatment or dipping. You should see the results of dipping a crankshaft for an 800HP engine. Rather awe inspiring if viewed from a distance.

DGG
Most cryo machines are heavily insulated boxes that cool by either of two methods. One method is to spray liquid nitrogen into the chamber and hope it doesn't hit anything. The second is to introduce liquid nitrogen below a false floor in the machine and circulating air over it. Temperature control is by a microprocessor based temperature control similar to the ones used on heat treating ovens, or by a personal computer with some sort of data board. Personally, I believe that trusting customer's parts the vagaries of microsoft on a computer in an industrial environment is risky.

The machines we use are vacuum insulated dewars with a heat exchanger. These are more costly, but have longer life times and a lot better efficiency. If you email me, I send you a URL where you can get a better description of these machines with pictures and such.

As for H1, (6-8Ni, .15C, 2Mn, 14-16Cr, .5-1.5Mb), it will respond to cryogenic processing. As you can see, it is a high carbon stainless steel that will precipitation harden into the range of about 58HRC. Expect greater wear resistance and ductility. It probably does not form any or very little Martensite.

Regards,
Rick
 
Rick, I thought I'd go with copper, as the thermal conductivity is higher, and expansion is lower. That's what I've seen on most cryo-coolers, plus I already have some...
Yep, no computer running it. A JC Systems controller should do it.
 
Bill:

You read my question exactly right - that is, is it a complete waste of time to do cryo in the home shop? I really appreciate your sharing the benefit of your experience. Sounds like it is working for you.

This is a great thread thanks to you and Warbird436 and others.

Thanks,

George
 
How does the average knifemaker utilize this technology. If the blade is not cryo treated after quenching, it will have retained austenite. Then if someone like OneCryo does the cryo, the blade has to be tempered and HRC adjusted to the makers disired hardness, by someone else. Meanwhile the blade is handled, shipped with the brittle converted austenite not tempered. There must be other companies that will do these things in house, but who?
 
I for one plan to continue utilizing the process. As per the comments above, I as a common knifemaker cannot perform the ultimate process with the equipment I have, but I can improve my blades by using what I have. I like all this technical stuff, but bottom line is I know it improves my blades from a technical standponit and a practical personal use standpoint. I have personally seen the benifits while butchering hogs and Whitetail deer and reports back from customers. I like having total control over the whole process without sending out.
 
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