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Ed Caffrey's Workshop Talk to Ed Caffrey ... The Montana Bladesmith! Tips, tricks and more from an ABS Mastersmith.

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  #1  
Old 06-14-2002, 03:08 AM
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Question Cryo-treatment

Ed,
Hmmm... I wonder what the effect of taking your ABS-JS blade instructions and then Cryo-treatment? Any thoughts?


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Old 06-14-2002, 07:12 AM
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Ed Caffrey Ed Caffrey is offline
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cryo.....

It will certainly work! I left that portion out for the sake of simplicity. After the final tempering, go into the cryo for 6-12 hours, then re-temper at 25 degrees higher than the previous tempering cycles. You will realize about 25% more cutting ability from 5160. And as long as you have edge hardened, there will be additional "springyness" in the spine.
The one area to watch is warming the blade back to room temp once you've taken it out of the cryo. Thermal shock is a very real possiblity here.......... I place blades between two layer pieces of ka-wool and let them warm slowy to room temp, then go to the temper.


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Old 06-15-2002, 09:50 AM
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Ed, what exactly do you mean by 25% more cutting ability? And how do you determine that?
For me 25% more cutting ability is a huge number that I just can't seem to relate too.






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Old 06-15-2002, 08:06 PM
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Cryo....

Speaking strictly on 5160 and 52100....
If you get everything correct..... anneal, normalize, harden, temper, cryo, and the last temper.
If all of these areas are equal, the cryo treatment on either of these steels will allow me to cut 20-25% more times on a 1/2 hemp rope before the edge goes. It is a significant increase. When I say that I refer to those of use who either are makers or use a knife everyday. I did a little experiment and gave one of each (a 52100 blade with cryo, and one without) to a friend of mine and ask him to tell me which on held up the best. After about a month of using them on the ranch, he could not tell any difference in the two blades..........however, the cryo treated blade, when tested in my shop, out cut the non-cryo blade by 25%. What I'm saying is that the average knife user often times cannot tell the difference. I have thought long and hard on this subject, and have wondered......when is enough, enough? We, as makers can tell folks all day long about the increased cutting ability, but if they cannot uderstand it for themselves, are we wasting our efforts? I will continue to use cryo, simply becasue it is peace of mind for me.........knowing I am only letting those blades out of the shop, that are the best I can produce.


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Old 06-16-2002, 09:26 AM
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Thanks Ed, that answers the question. Quite interesting.



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Old 06-16-2002, 11:57 PM
John Frankl John Frankl is offline
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cryo

Thanks Ed for the elaboration. I had a similar discussion with James Rodebaugh at the Oregon show. He mentioned working with 1084 and 52100 and realizing better performance from 52100. But he was also quick to point out that the differences were not apparent to his customers. Now I have a better idea of what he meant. This sort of brings us back to square one--use the steel you're comfortable with and bring it to its maximum potential--doesn't it?

John


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Old 06-18-2002, 10:34 AM
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I have been thinking this cyro stuff around in my head.

If the blade after cyro treating retains a 25% improved edge, is it 25% harder to sharpen?

Did your friend on the ranch keep a log of the jobs performed with both knives?

What is the cost of doing a cyro treatment?

Thanks


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Old 06-18-2002, 12:20 PM
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cryo

as I mentioned before, all the other steps in your themal treatments need to done correctly, and then the cryo. This will give you the increased performance factor.
With the cryo it is typical to gain a couple of Rc hardness points, but along with that comes the brittleness associated with hardness. That is why you must temper the blade again, after they cryo. Essentially you are transforming the left over austinite into martinsite by using the cryo treatment. This transforms the matrix into a tougher, more stable structure. That is not the technical explaination, but rather a general one of what occcurs within the steel. Basically austinite is an end to end platlet type structure, where as Martinsite is an overlapping type platelet structure. It's basically the same thing as joining two boards end to end versus joining them by overlapping them half way. If you can visualize that, then the differece becomes appearent.

There was no documentation of the tasks on the ranch......I likely would have gotten laughed off the place, had I asked for that! Over the years I have found that while it seems documenting performance equals proof.........it is very often impractical and more times than not taints the results in a day to day situation. I have come to rely more on the word of people using the knife, as they are more likely to speak the truth than to write it down.


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Old 06-18-2002, 03:44 PM
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Hi Ed, I don't mean to be disagreeable, I am just trying to get a relationship that means something to me.

I used a knife professionaly for years, as a big game guide up north, as a trapper, and as a ranch hand. I suppose a butcher would be more of a knife pro but I relied on knives alot.

A good knife is a blessing when it is being used daily for many tasks. Some tasks dull a knife faster than others in situations where it doesn't always make sense. Like peeling potatoes. Hard on an edge. Skinning a moose dulls a knife faster than skinning a deer.

I found that gaining a bit of edge retention was not always a good thing, if it meant more sharpening time.

I have a couple of knives that would be pretty awesome if they were to gain 25% in edge retention, but not if it meant 25% more sharpening time and not if it meant big bucks to cyro treat.


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Old 06-18-2002, 03:58 PM
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Ghostdog, this is how Terry Hearn put it:

Re: Cryogenic treatment

Don is right about the Finns putting they're knives in a snow bank for several month's. I read a story on this many years ago, seems like they claimed the knives cut better. Well I agree with them. I have been freezing my blades for over ten years now just in a regular ole freezer. Now someone once told me I was full of it and it wouldn't work, as Jerry said with less authorative sources the less likely of someone telling us what were full of. Heres what I found out after a lot of testing

Liguid nitrogen will bring a blade up an average of 1.5 points harder in approximently 8 to ten hours
Dry ice will get close to the same results but needs to stay in longer , around 24 hours.
Just a plain ole household freezer will bring the blade up around 1.5 points but needs to stay in about three days min,
approximently 72 hours, more time don't seem to make any difference.

Why this works the way it does I don't know, I just know it improve a blades cutting ability. Whatever the process you use ,just remember to heatreat, freeze, temper and temper again.

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(3/13/02 8:05:41 am)


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Old 06-18-2002, 05:08 PM
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cryo...

Ghostdog.....
Your not being disagreeable at all. I understand what your asking, just having a tough time making the answer sound right in written form.

I too have worked as a guide and on the ranch, so I understand where your coming from.

concerning the relationship of the cryo to sharpening, I have found that a blade of 5160 or 52100 is no more difficult to sharpen than one without cryo. In fact most forged blades react in this manner. Where it really gets to be a bear is on the high chromium stainless steels. An example would be 440C. Nearly all of the 440C blades that I have worked with (that have been cryo'ed) are a son of a gun to sharpen! One of the hardest critters I've found on a knife is pronghorn. With the dense, hollow hair they have, it's like cutting fine wire. Just as an example, the knife I built for myself last season was on of my mosaic damascus pieces, that I did cryo. It went through two elk, four mulies, and one pronghorn before it gave out on me.

As for costs, there are a few outfits that cryo commercially, but they tend to be spendy in small quantities. I opted to purchase an old "dewer" tank and do it myself. One of the local welding stores has a liquid nitrogen set up, and with the insulated box I built to contain the tank, I can get about 6 months on a single fill. The tank I have hold 56 lbs of liquid nitrogen, and costs about $80 to fill. I've not checked on the commercial prices lately, so I can't say if they are up or down from what they used to be.

Any knife you have cryo'ed will have to be broken down to just the blade. I goofed around a couple of times with some old knives to see what would happen when you cryo'ed a completed knife......not good. The handles split, and on one the edges literally chipped out during the warming process after the cryo. I think it's something that is best included in the overall process, and integrated into the overall building of a knife.

Don't worry about disagreeing with me.....I certainly don't know everything, and am always willing to listen to reasonable alternatives! I'll probably get enough flak about the 440C comment!


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Old 06-18-2002, 06:48 PM
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no flak from here, ed - the ONLY thing i have good to say about most stainless is that it stains less
.
having seen caution advised before about re-heating the steel coming out of the N2, i am wondering if the vermiculite used for annealing would help slow the warming process and protect the blade?
.
thanx


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Old 06-18-2002, 08:05 PM
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cryo...

I use two sheets of ka-wool, placing the blades between them which slows the warming process down to about 3-4 hours. The blade I mentioned in the previous post was between the ka-wool sheets when it "popped" . In fact I was in the shop hardening some EBKs at the time, and literally heard it go "ting!"


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Old 06-18-2002, 09:29 PM
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Thanks guys.

I don't think I will be doing any cyro treatment in the near future but 72 hours in the freezer is not too long.





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Old 06-19-2002, 08:53 AM
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Cyro

The home-freezer approach to cyro would be easy enough to do to add a little extra. I remember my dad, the master tool maker, saying they had a freezer in the shop they used for such. I believe they regarded it as sort of an extra normalization or stress relief for heat treated parts that required finish grinding etc.


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