At Home Cryo?

Stacy E. Apelt - Bladesmith said:
I was going by the smaller 10L Dewars that people often use. They seem to only last a month or so. YMMV. In either case, the Dewar and the LN refills are far more cost than $5 of dry ice and a gallon of hardware store alcohol.

The basic comment I was making was that by -100F the steel has fully hardened and converted into 100% martensite ( or as much as it will get) at -100F. There are eta carbides and other things changed in cryo, but they do not make more martensite. For the hobbyist home heat treater, sub zero is completely sufficient. Obviously a professional HT shop or full time maker who sells knives for a living will go with Ln and cryo.

From what I have read, there is some dispute among makers and metallurgists as to how much of the eta carbide changes survive the tempering. Personally, I doubt anyone but a metallurgical lab could tell whether it had cyro or just sub-zero.

All of the above is why I stress the value of a professional HT from Peter's (or some other experienced knife HT professional).... where they have the right equipment and know how to use it.
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I've heard from some that the average knife user, would barely tell the difference between the same blade with or without cryo. But, I have no experience with it. Once I get everything going I'm going to build a few blades from s30v, and test out dry ice, and then send a few out somewhere to get LN. See if the difference is noticeable or not.

I just looked up the data sheet for S30V at Crucible. The cryo temp they label at -112*. Will dry ice get that cold?
 
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Depending upon the steel alloy, -95 degrees Fahrenheit may not be enough. As has been pointed out by others in this thread, there are steels that require more - it's a Knifemaker's responsibility to know what steel they're using and what treatments it requires.
The number of knives one makes shouldn't have ANYTHING to do with what is used. If the steel requires a specific regimen, the correct tools should be utilized, otherwise a different alloy should be chosen. What's the point of making a custom knife if 'I guess this is good enough' is the target?

Peter's Heat Treat does excellent work, but there are some that wish to test the threshold of their heat treats, or don't make enough knives to make their $120 minimum a cost effective solution. Send out four batches at that rate and you've blown past the expense I've got invested in my dewar AND a couple refills.
 
colu41 said:
I've heard from some that the average knife user, would barely tell the difference between the same blade with or without cryo. But, I have no experience with it. Once I get everything going I'm going to build a few blades from s30v, and test out dry ice, and then send a few out somewhere to get LN. See if the difference is noticeable or not.

I just looked up the data sheet for S30V at Crucible. The cryo temp they label at -112*. Will dry ice get that cold?
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No, it will not.
 
Additional food for thought...

There are folks out there that attempt to perform unbiased edge testing. You may or may not lend credibility to their results or methods, however here's an example from one of our own BF forum members:

http://www.bladeforums.com/forums/showthread.php/793481-Ranking-of-Steels-in-Categories-based-on-Edge-Retention-cutting-5-8-quot-rope

Please take note that many of the alloys represented are used by a number of companies, with varying results, but that the knives that have performed 'off the charts' are done by 'home cryo' makers, neither of whom utilize dry ice for their steel alloys.
 
If you decide to go the Ln route just be very very careful I've heard that stuff will freeze off whatever it touches.Seen guys pouring that stuff out of the dewar because the knife wouldn't fit. Crazy.
 
Dry Ice is particularly useful for freezing, and keeping things frozen because of its very cold temperature: -109.3°F or -78.5°C. Dry Ice is widely used because it is simple to freeze and easy to handle using insulated gloves. Dry Ice changes directly from a solid to a gas -sublimation- in normal atmospheric conditions without going through a wet liquid stage. Therefore it gets the name "dry ice."
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http://www.dryiceinfo.com/
 
I called Crucible this afternoon to ask the same question, but the person in sales is away until Monday. I did send an email asking the question just in case I forget to phone next week.
 
Lo/Rez said:
I called Crucible this afternoon to ask the same question, but the person in sales is away until Monday. I did send an email asking the question just in case I forget to phone next week.
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You'll have to let me know if they get back to you! I'm running dangerously low on blade steel. I've been holding off my order as I am going to pick up some stainless also. Just need to figure out what I will be capable of working with, WITHOUT having to send blades out anywhere.
 
The data sheets are out there if you look for them. If you expect to work with high alloy steels/stainless, you'll need temperature control in the form of a PID controlled oven and high temp stainless foil. Many "air" quench steels also will benefit from plate quenching and sub-zero quench with dry ice, true cryo to get the most out of it.

--nathan
 
silver_pilate said:
The data sheets are out there if you look for them. If you expect to work with high alloy steels/stainless, you'll need temperature control in the form of a PID controlled oven and high temp stainless foil. Many "air" quench steels also will benefit from plate quenching and sub-zero quench with dry ice, true cryo to get the most out of it.

--nathan
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I'm in the middle of building a digital oven. That's why I'm trying to get as much info on the cryo as I can before I just jump into stainless.
 
i helped a guy out that was testing both 154cm and cpm154 with both being HTed with and withought LN cryo and i can tell you for fact i coudl tell what i was grinding. i helped a maker tune the HT for cpm154 in his shop (no cryo) and while he got ok HT after he tried one i did the full HT with cryo he asked me that for the now and then SS blades he gets an order for if i woudl HT them (he is a smith and doesnt do many SS blades so its not worth it for him to have a dewer
 
colu41 said:
Interesting. Well with that, dry ice would be perfectly fine for Cpm154. But its 3 degrees off for s30v lol. Would that make a difference?
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What many don't grasp is that the Mf isn't a switch that flips "ON" at -112F ( or whatever). It is a point at which all austenite has converted to martensite. -90F and -112F may sound far apart, but the difference may be as little as 99% or 100% martensite. That is a difference that is insignificant.

For the basic stainless steels, like CPM-154, 440-C, AEB-L, etc, a dry ice slurry is fine for reaching a suitable Mf.
 
There's no mention whatsoever in Crucible's documentation that states that -112 F is Mf. What they state is that is the temperature required to achieve the transformation. I find it odd that somehow this can be translated into ANY other close number. If it wasn't that important, why would the engineers and metallurgists have specified -112, do you think? Doesn't it seem as if it would have been easier to say -110, or even state to "approximately -112"?

There are additional factors involved here that aren't worth going into, as its rehashing ground that's already been gone over, but if you're a savvy maker, and are paying attention to what's been covered with other heat treat discussions, you'll find that the temperatures we refer to move dependent upon austemps, quenchants and rate of quench, etc.

Find out what is 'enough', and why. THEN decide if these alloys are right for your needs, and use accordingly. If ,'good enough' is what you're shooting for, disregard this.

Heck, if 'good enough' was good enough, I highly doubt this question would have been asked in the first place!
 
You might say we agree 99% on what you are saying :) We are picking at opposite ends of the same loose thread.


I get what you are saying Matthew, but it isn't an ON/OFF situation. The transformation gradually happens as the temperature drops.( using example numbers) At 400F it starts, at 200F it is 50% done, at 70F it is 80% done, at -30F it is 90% done, at -95F, the transformation is probably 99% complete. The -112F it is 100% complete. The difference between room temp finish and -95F finish is significant. In the real world, no one would say 99% is bad and 100% is good.

Examples of similar transformations are:
Water boils at 212F at sea level. An egg will cook in boiling water in 5 minutes. If your boiling water is 209F on a tall hill, your egg will still cook. It might take a few seconds longer, but that is insignificant....and they will still state that water boils at 212F, and eggs cook in 5 minutes.... even though we all know that isn't exactly correct.

If the lethal dose of a drug is 400mg, a dose of 390mg will still make you very sick. It might even kill you. That won't change the books from saying the lethal dose is 400mg.

If you crash into a brick wall at 90mph it will be really bad. If you crash into the same wall at 85mph, it will still be bad. It might do a tad less mangling of the car and passengers, but no one would say that a crash at 85 is good and a crash at 90mph is bad.


Again, I get what you are saying empirically, but for the home HTer, it isn't enough to be all that significant. Everyone should strive to do the best they can do with the equipment and skills they possess. It is not necessary to buy higher quality or extra equipment just to gain a tiny percentage if the simpler methods or equipment will suffice just as well.

I'll let this go now, as it is starting to drift away from the question of LN vs Dry Ice. Suffice to say that the subject is one with many opinions.
 
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We should come up with a chart as a sticky. "Steels to use with Cryo (LN) vs Steels to use with Sub Zero (Dry Ice)". If the steel isn't listed.....it doesn't need either.

S30V....Cryo.
 
Where is mete/Robert? He mentioned quite a bit about cryo & eta-carbides:thumbup:; however learning is on your own. Hexagonal closed-packed structure is very cool for some ht configurations.

LN2 vs dry-Ice(or compressed CO2) vs room temperature? it is not simple a case of when in doubt - CYA - use lowest quench temperature. When alloying elements volume go up and lot of carbon in solution, Mf temperature is proportionally lower. If your ht process produce large percentage of RA at Mr (martensite at room temp), critically we should ask why first and then think whether deep cooling is part of natural thermal chemistry or is it an alleviation of excess FCC structure mostly due to spatial (spacing + potential energy barrier) problem.

For given specific steel condition, ht params, etc.. much easier to come up with a recommendation whether Mr is good or how much below 0C is good.

* warning - for those that curious & have time to burn on learning instead of making cool knives. *

https://en.wikipedia.org/wiki/Crystal_structure - luckily we only concern with #7 and #5 and nifty cool #6.

https://en.wikipedia.org/wiki/Atomic_packing_factor - BCT is ~ 0.704

Can be rewarding to look at ht in perspective of: spatial, energy (thermal, potential), atomic covalent
 
I'm right here ! It took me a very LONG time to find out about eta carbides . Much bs about it even by "metallurgists "- shameful ! The fact is simple , you are forming a very small carbide with cohesion .That means both the carbide and cohesion [forces that stress the matrix around the carbide therefore increasing the strength .] Cohesion is also formed during the high temp secondary hardening of some alloys ! For those alloys that can benefit cryo will increase strength and wear resistance . No black magic just an understanding of the metallurgical processes. And as Butch says - you can do the HT right - then screw that up by final grinding !!!
 
I used dry ice/alcohol on several steels before I got my dewar and I'm here to tell you LN makes a difference in any steel that needs to be quenched below room temp.. Those differences vary from alloy to alloy but I'm here to tell you that those ETA carbides the other guys are talking about are REAL. What I find interesting is that the Austenite conversion takes place on the way down but the ETA carbides are formed on the way back up from what I understand.
Now that I have a dewar I find LN to actually be cheaper in my experience. I have a 30 Liter dewar and it costs me $30 to fill it. It lasts 6-8 weeks depending on use. Mine has a 3" mouth and needs a new bung which is probably why mine needs filling a bit sooner than others. Like I said, its still cheaper for me than dry ice and I have NO doubts about the quality of my H/T.
My bottom line opinion is, if you're gonna use high alloy PM steels you should do what it takes to get the most out of them but that's just me. BTW, I have a few knives on that list Matt is talking about.;)

**EDITED to answer your original question. A Dewar and access to LN is all you need. I see you're in MI so you should have no problem locating someone who uses LN in breeding cattle. That is the best place to find a used Dewar. I lucked up and got mine for $150 so deals are out there if you take your time and be patient. Good luck.
 
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is there a chart that shows what steels benefit from cryo? either dry ice or LN? i am working with 0-1 tool steel and 1095. will either of these steels benefit from cryo? If so, dry ice or LN?
 
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