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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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Old 08-29-2004, 08:59 AM
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Ed Caffrey Ed Caffrey is offline
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Your mehtods for cryo treating..gathering data

I had an interesting conversation yesterday, concerning cryo-treating blades. The methods used by the individual I was talking with at first seemed odd, but the more I thought about it, the more sense he made. Anyway, it made me think about the various methods that we use, so I thought I would ask a couple of questions to everyone here.

First, at what point do you cryo-treat your blades? What are your thoughts of the duration required for cryo-treating? (time) And, do you cryo-treat a specific blade more than one time?

For 52100 my method is to multiple harden the blade, conduct a "snap" temper, and then go into the cryo. Duration wise, I go for 6-8 hours in the cryo, and allow the blade to warm slowly back to room temp by placing the blade(s) between two layers of ka-wool. I follow this up with a triple temper, and then complete the knife.

So, don't be bashful........what methods to you use for cryo-treating your blades?

"Nobody cares what you know.....until they know you care."
See me at table 2Q at the Blade Show!
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Old 09-01-2004, 04:07 PM
Michael E. Mill Michael E. Mill is offline
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When I do my own cable and layered damascus, I double temper then cryo then temper one more time. Most of the time I have 5 or 6 blades together and when cryoed do it for at least 6 hours and most of the time I put them in in the evening and return the next morning to get them out. I use a friendly farmers semen tank of liquid nirtrogen suspend them with stainless welding rod thru holes in the tang and suspend them slowlyuntil submerged. On my stock removal blades of D2 and ATS 34 I cryo them after they come back from a commercial heat treater and then temper them at 300 degrees for two hours. I have taken several of my knife store friends blades from commercial knives out and simply submerged them for the time period and they are amazed on the increased edge retention even if the factory says they are cryoed. I wonder then about the length of time they do them. For me at least 6 hours on everything and most end up 12 hours AND I FIRMLY BELIEVE IT HELPS. Mike
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Old 09-10-2004, 05:25 PM
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mete mete is offline
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The problem with tempering and cryo is that tempering stabilizes the retained austenite preventing it from being transformed to martensite. There is some danger in going directly from quench to cryo as far as cracking so some will 'snap temper' but that must be done at a fairly low temperature such as 300F.Higher temperatures such as 400F will definitely stabilize the austenite.My suggestion would be to quench, snap temper at 300F for 1 hour , cryo,10 hours would be more than enough, then double temper.
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Old 09-19-2004, 10:03 AM
canyonman canyonman is offline
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Since I do most of my work(stock removal, 1095)on the weekends, I harden then a quick temper of 30 mins. @ 325F then I put it in my home freezer for a week or longer.
My question is do any of you think I'm doing any good or is this just a safe way of storing unfinished projects?

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Old 09-20-2004, 06:42 PM
Quenchcrack Quenchcrack is offline
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Cryo in the freezer

To put it into perspective, most high carbon steels achieve about 90% martensite when quenched down to room temperature. To get the other 10% you must cryo treat it. There is a somewhat linear relationship between the temperature at which you freeze it and the amount of martensite formed. LN is about -300F and your home freezer is about +32F. If you quench to say, 70F, there is a total of 370 degrees you need to get below. If you only freeze down 70-32 = 38 degrees, you have gone 38/370 or 10% of the remaining 10% or about a 1% improvement. Modest but better than a poke in the eye with a pointy stick.

Let me add my firm agreement with the comments regarding tempering and cryo treating. Austenite at room temperature is metastable; it does not want to be there! Tempering will cause the retained austenite to decompose to bainite or even pearlite. Once it has transformed, the cryo is not doing much. Quench it, snap draw it at 250F-300F for about 1/2 hr, cryo and retemper at your normal temperature.

Which is worse; ignorance or apathy? Who knows? Who cares?
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Old 09-20-2004, 09:41 PM
AwP AwP is offline
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I haven't done any cryo yet, though now that I read that even a home freezer can have a slight effect I might have to start thinking about it a little more. I did have a couple questions though...

Tempering will cause the retained austenite to decompose to bainite or even pearlite.
Is there a way to force the retained austenite to bainite and be sure not to get pearlite without marquenching and making the whole thing bainite? I'm thinking a mix of martinsite and bainite might not be a bad thing on a heavy duty chopper.

The methods used by the individual I was talking with at first seemed odd, but the more I thought about it, the more sense he made.
Just purely being nosey, but what is this persons unusual method?

~Andrew W. "NT Cough'n Monkey" Petkus
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Old 09-21-2004, 12:55 PM
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mete mete is offline
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I hope your home freezers are colder than +32F because the colder it is the longer you can keep food .It should be no warmer than +10F and preferably -10F. However even if it's -10F the influence on heat treating will be minor......AwP, you're confusing terms .Austempering gives you bainite. Marquenching or martempering gives you martensite.Typically the retained austenite will decompose to martensite at typical tempering temperatures [ below Ms ] I wouldn' try to produce duplex structures.... Also I should mention here that excessive austenitizing temperature will produce excessive retained austenite .
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Old 09-21-2004, 01:51 PM
AwP AwP is offline
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Austempering gives you bainite. Marquenching or martempering gives you martensite.Typically the retained austenite will decompose to martensite at typical tempering temperatures [ below Ms ] I wouldn' try to produce duplex structures....
Oops, austempering, I do get those two terms confused alot. So mixing martinsite and bainite isn't really something that'd be possible with a hope setup? Or is it that it's not as desirable as my armchair theory makes it seem like it would be?

~Andrew W. "NT Cough'n Monkey" Petkus
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Old 03-13-2017, 01:08 PM
Blade-Runner Blade-Runner is offline
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Hi Everyone!

I am fairly new to the knife making world, and extremely interested in performing a cryogenic treatment on my knives to really improve their performance. However, there doesn't seem to be a whole lot of companies building smaller machines out there. With some searching, I found one place that builds smaller machines for around $6k US, which was by far the best I came across. However, I am curious if anyone out there has any suggestions on where to get a machine, or of any respectable companies that build smaller machines to fit a custom knife makers size, and of course, our budget?
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Old 03-13-2017, 01:37 PM
mr.HC mr.HC is offline
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austa, bainta, marqta, you guys lost me right from the start, could someone please speak English so I can follow along lol

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Old 03-13-2017, 11:51 PM
jimmontg jimmontg is offline
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13 year old thread.
Blade Runner what type of a machine are you talking about for doing cryo? For $6000 I can buy you a 24" deep Paragon oven and a $300 dewar for holding liquid nitrogen. Plus build you a dry ice freezer for metals like AEB-L which only cryo at -95F and dry ice is -109F. AeB-L is a great knife steel and one of the easier stainless to HT into knives. After all that still have $2000 leftover, are you talking about a deep freeze freezer that go to like -80F?

Properly built dry ice chest should hold dry ice for 2 to 3 weeks, please note dry ice isn't a dct or deep cryo treatment and it takes three days under the dry ice to see the difference depending on steel of course. AEB-L only needs to be dropped down to -95F and let it slowly warm up, it doesn't need to soak. I use dry ice on O1 as it definitely makes it tougher and I can temper it a point higher without the brittleness.

My friend Dtec did an experiment for me with a 440C blade. The blade was finished final HT and cryo and tempers all done. Dave left the knife all night in LN and measured to 4 x and got an increase of .9, almost a whole RC point. That is significant and a small temper would be needed afterwards, but on a finished knife the increase surprised us both.

Cryo can be kept simple or you can get complicated with it. It most definitely make blades better, and you can build an ice chest with 4" thick walls, but it has it's limits too. 3 days under dry ice will make most steels tougher as will overnight with LiqUid Nitrogen. LN also makes the little eta-carbides and will make the steel harder. As for snap tempers before subjecting the quenched metal to super cold temperature well I have been told it isn't necessary, but I would still do it to D2 as I've never had a failure with it. D2 is triple tempers with cryo in between, I get 59-61 hardness, 60 mostly and that is my target. Only ever cryoed it with dry ice.
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Old 03-14-2017, 10:54 PM
Blade-Runner Blade-Runner is offline
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So, it's a machine specifically designed for a completely controlled submersion in liquid nitrogen. However, it drops the temperature slow enough that there is no worries about thermal shock. It allows you to program your ramp rate and soak time.

I have become fairly familiar with cryogenics since school, and have come to realize that there are quite a few misconceptions about how it is supposed to be performed. So I came to the forums to see how most other knife makers were doing it.

I have also read the following on Jay Fisher's website:

"What is the specific rate of cooling for most of these steels? 4-5 degrees Fahrenheit per minute. That means in order to reach -100?F, it should take about 40 minutes (from room temperature), and to reach -325?F should take about an hour and a half (from room temperature). This is why simply dipping blades into cryogenic baths of dry ice and alcohol or liquid nitrogen is a huge and destructive error, yet knifemakers who are uneducated in this process frequently do this, and tell others that it's the proper way to quench! Sad, truly sad for the knife client. The cryogenic process cooling rate is absolute and critical."

And I have yet to read anything that replaces a machine of this type. I am still in the learning curve, but I think it's an interesting concept.
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Old 04-15-2017, 01:23 PM
samuraistuart samuraistuart is offline
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I don't know of many knife makers at all that do CONTROLLED drop in temperature to -300F with LN2. I am not a metallurgist, but would say that is not needed.

Terminology, as with many things, is important so that we are all on the same page when discussing things. Generally speaking, us knife makers have 2 terms we use. "Sub zero" which refers to the dry ice slurry temps of -100F, and then "Cryo" to refer to LN2 temps of -300F. Shallow cyro, deep cryo, as Jay uses them.....that's fine too. But like I said, most knife makers who cryo are lucky to find/afford a dewar with a mouth wide enough to insert a large blade. Very very few would invest in a machine that drops the temp to -300F in a controlled manner.

And just to add to this discussion about exactly WHAT we are trying to accomplish with "cryo" or "sub zero". By FAR, by FAR, the biggest reason to use SZ/Cryo is the elimination of retained austenite. As a steel is quenched, the austenite state is transformed to martensite. However, some steels have a martensite finish temperature below room temp. O1 is NOT one of them. 52100 is NOT one of them. A2....yes. D2...yes. And of course, stainless steels and higher alloy tool steels like AEB-L, M4, etc. If you see gains in HRC reading by employing SZ or Cryo with need to re-think your 52100 heat treat. A2 and D2 have enough retained austenite that a sub zero dry ice treatment will help to convert much of that. Cryo, LN2, will convert nearly 100% of the RA. I think many aren't getting this concept.......the MAIN reason by FAR, again, just to stress it, of employing SZ/Cryo operations is the elimination of retained austenite. The 2nd benefit is the formation of super small "eta" carbides that will precipitate upon tempering....but this is ONLY happening with LN2 temps of -300F and SOAKING for a number of hours.

Back to Sub Zero. As I mentioned, there is no eta carbide precip going on with sub zero dry ice temps. All that is happening with dry ice is RA elimination. And martensite forms at the speed of sound. mach 1, thereabouts. There is NO NEED TO SOAK A STEEL when using sub zero dry ice for hours. Once the steel reaches the dry ice temperature, the martensite is converted, instantly. Soaking in dry ice any longer does nothing. Nothing good, nothing bad. I leave my knives in dry ice slurry until the dry ice has evaporated (overnight).....but again, the transformation we are after happens at the speed of sound, at the instant the steel reaches the dry ice temperature.

About tempering.......the ONLY time you should employ a snap temper BEFORE cryo is IF you are concerned about warping. Tempering stabilizes retained's just a fact of life. If you TEMPER BEFORE CRYO, you are severely hampering the ability of the sub zero/cryo treatment to do it's job......change RA to untempered martensite. A PROPER quench is done in a continuous temperature drop. For a carbon steel like D2, that means it should be quenched from it's hardening temp of 1850F all the way down to room temp, then IMMEDIATELY into the SZ/cryo chamber, then back up to room temp, then temper. If you temper before cryo, you are interrupting that quench cycle, and stabilizing RA....which again sort of negates the whole purpose of sub zero /cryo. I know what the "books" say, but NONE of those "books" are talking about making the best knife, but rather bearing, dies, mold, etc.

If you are seeing changes in O1 HRC readings, or 52100 HRC readings by doing sub zero or cryo, your HT is off. The Mf of those 2 steels is well above room temp. Sub zero will not make either of those steels tougher. However, Cryo with LN2, due to the precip of the eta carbides, not only makes it tougher, but slightly more wear resistant. NOT 400% more as is claimed by cryo companies selling cryo products.

Last edited by samuraistuart; 04-15-2017 at 01:29 PM.
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