cryo and knives?

B

BladeGuru

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Aug 14, 2009
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Has anyone cryo'd their blades and if so did you notice anything truly beneficial about the process or is it all just fluff? What I find on Googs is just a lot of places here in AZ seling their wares.

Not the best place to get data, no wot I meen?

I'm probably going to use toolsteel to make a barong.. haven't decided which... and then I'll send it to a reputable heat treater.

So the process is cut out the blade and shape it, send it to a treater and follow that with cryo.

Any input?

This project is near and dear to me. I've made carbon steel barongs before but this blade Im talking about here is a prototype for a limited edition for my students.

Only students will be able to purchase these, so it has to be right.

Thanks so much,

BG
 
One of my first postings was on the same subject but their is two different levels of cryo. The first that is most common is to take the blade to -125 but that is in the middle of the HT process. The other is to go much colder at -300 but no one seems to know anything about it. A company called www.cryoplus.com is one that I am thinking of sending a blade to, to see it their is really any noticable difference. Its seems to popular with mining and high performance car motors and parts but not much talk in the knife world.

Its pretty much a dead end subject here as I found out, one of those thing you just going to have to try for yourself.

Welcome to BF
 
It is huge in shooting as well, and I would think cryo would have a pretty significant effect on a blade's resilience to stress. I never even thought about applying it to blades before though...
 
Cryo is always part of the heat treatment not something added later !! There is much hype about cryo and I as a metallurgist am embarrassed by the BS. We do know that cryo will reduce retained austenite but that's all that has been proven !!
Shooting ? Benelli has photos through a microscope of cryo'd and un-cryo'd barrels - they are not possible ! I have an older Benelli and it doesn't have or need cryo ! NRA and some top barrel makers have found no difference with cryo .Krieger makes lots of claims but they have the equipment
I would suggest for best performance of the air hardening steels such as A-2, 154CM, S30V etc that cryo be used . It can add 1-2 HRc points .
 
mete said:
Cryo is always part of the heat treatment not something added later !! There is much hype about cryo and I as a metallurgist am embarrassed by the BS. We do know that cryo will reduce retained austenite but that's all that has been proven !!
Shooting ? Benelli has photos through a microscope of cryo'd and un-cryo'd barrels - they are not possible ! I have an older Benelli and it doesn't have or need cryo ! NRA and some top barrel makers have found no difference with cryo .Krieger makes lots of claims but they have the equipment
I would suggest for best performance of the air hardening steels such as A-2, 154CM, S30V etc that cryo be used . It can add 1-2 HRc points .
Click to expand...


The company I linked uses a process that they say works after HT, its also a little different from your normal cold dip. They take the steel to -300 then warm it back up to +300, that's much colder and much different than the sandard -125 dip. Their has to be some advantage to the colder treatment right?
 
There was an article in Blade years ago that said the number and density of the carbides went up with the -300 treatment. This was on D2. The wording was somewhat suspect, and was from advertising literature.
 
Sometimes I don't believe what I read, people will rave about crucibles steels and
how good they are but question whether or not it relly needs cryo. Crucibles book
on tool and cutlery grade stainless suggests it straight across the board for all of
them and most of the cutlery grades of carbon steel. Is this doubt or question
because its easier or an omitted step? or is it because the people making these
great steels don't know what they're talking about? Speed costs money- how fast
do you want to go?
Ken.
 
Finally...a subject that is interesting, keep posting Gentlemen....so that I may learn something new.
 
Knives Illustraded had a comprahensive article on this about a yr. ago.the steels that most improved were the more complex alloys.ats34 440c d2 154cm etc.they had a chart with cutting tests before & after cyro.treat.i beleive they used 1/2 in. sissal.liquid nitro.was the quench & most of the blades cut 3 times more rope.they stated the martenistic transformation was much improved resulting in finer grain & stress free metal.some of our custom guys are doing this& maybe they will give us some info.
 
mete said:
I would suggest for best performance of the air hardening steels such as A-2, 154CM, S30V etc that cryo be used . It can add 1-2 HRc points .
Click to expand...

I've tried it with A-2. It made the blade more brittle forcing me to temper it again. Pretty much all my stainless steel blades have already been cryo'ed during the heat treating so there doesn't seem to be a point.
 
Cryo does not effect grain size . That's BS #1. That is only determined by prior austenitic grain size and quenching !!!
Cryo must ALWAYS be followed by tempering. This is because cryo transforms retained austenite to brittle UN-tempered austenite .So it must then be tempered !
 
mete said:
Cryo does not effect grain size . That's BS #1. That is only determined by prior austenitic grain size and quenching !!!
Cryo must ALWAYS be followed by tempering. This is because cryo transforms retained austenite to brittle UN-tempered austenite .So it must then be tempered !
Click to expand...


Would +300 be considered a temper?
 
There is a ton of misinformation on how and what cryo treating does. As mentioned above, the cryo tempo can transform virtually all of the austenite in a part to martensite. Martensite is the really hard brittle structure that you have to temper if you want a useful toughness. If there was austenite in your blade after it was all done with traditional heat treating methods, cryo could actually make your knife more brittle.

Many HT recipies call for double cryo, double temper, but the cryo is always before the temper and after the quench.

One last thing, it is not a real good idea to dip your blade into Liquid Nitrogen. You can get significant stress differentials at the liquid/vapor interface, which could lead to a weak spot. The commercial freezers use a very fine spray of liquid that converts almost instantly to gas. Eventually the inside of the freezer is down to about -300 or so due to this cold gas.

I am not necessarily sold on the absolut need for cryo treating blade steel. One of the reasons you get retained austenite is differential cooling. The inside of your blade cools slower than the outside since the outside is in contact with the quench medium. Technically, it is a question of how fast you get to the nose of the TTT, how close you shave the curve and a bunch of other BS In theory, you would have more austenite in the middle of any quenched section. I think that many knives are thin enough that they cool essentially at the same rate and any retained austenite issues are more alloy related. All that being said, I dont think it hurts as long as it is done during the HT process and done without direct liquid contact. I am rather skeptical about the martensite transformation benefit after tempering.

As far as a tempering temperature, 300 is probably a bit low for most steel, but you have to use whatever works
 
Some use +300 F as a 'snap temper' before cryo. I consider it low for any other purpose. +350 and +400 F are more typical starting temperatures.
 
Usually I try to suspend my blades above the LN, can I prove it? no------ but
I do believe.
Ken.
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By saying I try to suspend them above the LN I mean while inside the dewar, and
even though I can't prove what it does I'm the one doing the grinding and thats why I say I believe
Ken.
 
Ken, what kind of improvements do you notice?
 
To me it seems to grind more like cpm (usually I'm using ats) and theres a definite
difference in how hard the blades are to grind more like trying to grind D2 though
I freeze that too. I believe I can grind the edge thinner down to about 5 thou and
not have to worry about chipping. Also I draw at 950 instead of the lower temp.
Ken.
 
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That's the first positive comment I have seen and it makes me happy. I have been wanting to send a blade to cryoplus for a long time and I might just do it now. Any specific steels besides D2 that work well?
 
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