Cryoing your own knife?

B

bubblewhip

Joined
Dec 18, 2009
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I was wondering because Liquid Nitrogen is a possible thing to obtain that it would be possible to do a deep cryo treatment on your own knife if it wasn't done for you. Has anyone considered it? Tried it? Is it even a decent idea?
 
It would be very interesting to see a head to head cutting test between a stock and cryo'ed blade, since cryo is generally not performed in the industry, except for Busse.

There seems to be a lot of controversy whether post-temper deep cryo does anything, with nobody performing any actual tests to settle the debate. It does refine carbides, but in theory smaller carbides don't do anything for wear resistance as the total carbide volume is still the same, might improve toughness though that is not something that is easy to measure.

Some custom knifemakers use pre-temper cryo, which is different as it's needed to complete martensite conversion. You get an instant 4-5 point rc increase with certain steels so there's no debate there.
 
It's part of the HT process , not an add-on !!!
It does NOT refine carbides !! It creates new small carbides [eta carbides] .The larger carbides remain the same.
The proven benefits are that cryo reduces the amount of retained austenite .This converts to martensite but the hardness increase is only 1-2 HRc points ! [this is typical of stainless steels like 154CM etc]
 
mete said:
It's part of the HT process , not an add-on !!!
It does NOT refine carbides !! It creates new small carbides [eta carbides] .The larger carbides remain the same.
The proven benefits are that cryo reduces the amount of retained austenite .This converts to martensite but the hardness increase is only 1-2 HRc points ! [this is typical of stainless steels like 154CM etc]
Click to expand...


This is not a -125 cryo is a -300 and yes its done after the HT, take a look at the site I have linked.
 
I think Mete is speaking of the -300 cryo treatment and for that 2RC improvement is normal with refinement of the eta carbides . DM
 
Well, the post-heat treat cryo won't increase the hardness at all if it's been properly tempered. Cryo as part of the heat treat (pre-temper) usually increases the hardness 1-2 rc points but if higher austenizing temperatures are used you can definitely get more increase than that due to the retained austenite.

Mete is our resident metallurgist and is extremely knowledgeable. That said, his viewpoint is at one end of the debate. The cryo companies take the other side of the debate, claiming that you can get better wear resistance with post-HT cryo. Some people think they are shams, but they do publish their testing.
 
Why is it that we can't simply dip the knife into liquid nitrogen after the heat treating process? Wouldn't that still refine the carbides?
 
Cryogenic treatment is -300 F [liquid nitrogen]. Dry ice [solid CO2] is -100 F and is what we used to call subzero treatment. When you reduce retained austenite that will turn into UNTEMPERED martensite .This MUST be tempered as it is very brittle.
 
That's why I gave the link, they use a controled cycle from -300 to +300
 
Bubble, I suppose you could . A Dewar will cost several hundred dollars and one could temper in a kitchen oven and the LN1 will cost $30 depending on how much . Be careful the way you handle LN1 as its in a unstable state and can boil out and burn you . How much good you'll get out of it is questionable . I'm with Mete . DM
 
Here's a little info on various knife steels with and without cryo in tests done by Wayne Goddard. It's not comprehensive but gives an indication of what is possible. Note: See why I like Vascowear so much, and would love to try the powder steel version of it, PD#1. It's tougher than D2, but it does rust. It's the father of CPM3V

http://users.ameritech.net/knives/edge.htm

Wayne Goddard's Edge Holding Tests
Return to Steve's Knife Sharpening Page
Twelve years ago I started using a standard test to test the cutting abilities of different knife steels. All the blades I prepare for this test are the same size, shape and thickness, being .125 in. thick and flat ground. The included angle is 12 degrees to 15 degrees, with a primary sharpening angle of 15 degrees per side; final sharpening is on a Norton Fine India stone. Cuts are made on the single strands out of a 1 1/4 in. hemp rope. The single strands are easier to handle.
Three tests were conducted on each blade and the results averaged. Using a slicing cut, the strand is parted and cutting continues until the cutting edge loses its bite into the rope. This is about the same point that the edge loses its ability to shave hair.


Steel Type Rockwell "C" Hardness Number of Cuts
154 CM Freeze treated 61 44
154 CM Not freeze treated 60 38*
ATS 34 Freeze treated 60 38
440-C Freeze treated 58 33
440-C Not freeze treated ? 25*
CPM T440-V ? 58
VASCOWEAR 61 56
D-2 60 47
D-5 61 52
D-5 59 40*
Stellite 6-K 44 58
F-8 ? 45
M-2 64 44
52100 Handforged 60 43
5160 Handforged 60 43
O-7 Handforged 61 44
*Note the difference that two points of Rockwell hardness makes, also the loss of edge holding when freeze treating is not used.
There is a lot of difference in rope; some is more abrasive than others. I keep a standard knife on hand to compare all others to; this will tell you also when your rope changes.
W. L. Goddard
 
For steels with low temper, cryo is needed as higher alloyed steels tend
to have lower martenside transition finish temperature. That is, cryo
is a part of hardening process in heat-treatment cycle.
Thats why higher hardness and better edge retention is achieved in cryo treatment.

This kind of theory makes sense to me but honestly I've got no idea
how chilling finished blade makes a better edge.
 
Fuj, That exactly what Mete and I are saying . But some think you can do better the second time around . DM
 
Cold and cryo treatments have been debated here since the site started. Something to keep in mind about all the claims: you have to know the procedure to make meaningful comparisons of all the performance claims. Some claim an increase in carbide volume, some claim an increase in hardness, some show an elimination of the secondary hardening bump in some steels. The trouble is, all these things can happen and all can have different procedures that lead to the same end result. There is a paper linked here somewhere that discusses all the claims and how each claim can be supported, but only by playing with different rules.
 
Me2, I seem to remember having read that way back and didn't agree with it then . But now I realize their statements are as you say from, "playing with different rules" . Well put . DM
 
After dealing with ASTM (american society for testing of materials) for 10 years, I have come to the conclusion that not following their procedures does't mean you did it wrong, but you will have difficulty comparing your results to everyone else. I think that is what we have with cryongenic treatments of blades.

On topic content: I have a blade that was cryogenically treated post heat treatment. My personal belief is that it should be done after quenching and before tempering, except maybe a snap temper if the steel requires it. I would need the same blade without post heat treat cryo to test its effectiveness. I can say the blade takes a wicked edge and holds it well. However, mild steel can be made to whittle hair and edge holding is very subjective. I mainly use this knife for cutting jute twine for weaving slings and pouches. Surprisingly (:rolleyes:) I have not resharpened it in 6 months.
 
busse discussed this in some length back awhile. he stated that a sudden drastic temp change could cause micro fractures in the matrix. his procedure is to take the temp down gradually to the cryo bath. then bring it back up slowly along with other procedures to make infi. i believe him because his blades prove his process.
 
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