cryo advice

C

'cacci

Joined
Jul 24, 2008
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I'm about to try cryo treatment for the first time. I use the accepted procedure for D2 in my ht oven. I remove the wrapped blade from the ht oven and allow to cool to 125 to 150. I quickly unwrap and reheat in a preheated kitchen oven to 450 for 2 hours. I remove and allow blade to cool to room temp. I reheat in a preheated oven for 2hours at 425. I get 58 to 59 Rc. To introduce the cryo, what changes do I make?
I plan to use dry ice in a 6-packer cooler. Can I simply place the blade in the cooler next to the ice? How long do I keep the blade cold?
Thanks in advance for any help.

'cacci
 
Everything sounds good here are some tips.
For one dry ice is a sub zero treatment not cryo. Cryo can be achieved with liquid nitrogen.
This is my personal procedure
I plate quench straight from the oven. When it cools to room temp I remove from foil and do a cryo or sub zero treatment which ever you prefer.
Then I do the tempering cycles.
For sub zero I have done this two ways with no noticeable differences in performance.
1) mix dry ice with kerosene or denatured alcohol into a slurry,in a cooler submerge blades overnight.
2) sandwich blade between dry ice blocks ( in a cooler) leave overnight.
I won't go into all the reasons ...here for skipping a tempering cycle before cryo / sub zero but it's proven to reduce more RA.
Also, if you need any help feel free PM me or call 731-514-8731
Jason
 
Don't temper at 450 before the sub zero/cryo.

From the oven either air cool or plate quench toward room temp. When below 120F ( room temp is OK), do a snap temper at 300F for 30 minutes. Quench in water to cool and then place in LN or dry ice slurry. After the subZ/cryo, warm to room temp and do two tempers at 450F for two hours each. Cool between tempers by quenching in water.

If using dry ice, there is no need for an extended soak at -100F. Give it 30 minutes or an hour, just so the dry ice doesn't seem such a loss, and then let warm up to room temp. Five minutes or five hours won't change a thing. Once the steel is fully at -100F, the conversion from austenite to martensite happens in a fraction of a second. In cryo,at -300F and lower, other things happen that need time, but not at -100F.

When asked why just putting the blade in with the dry ice isn't as good as using a slurry, I use this example:
Place you hand over the dry ice...really close, but not touching. Feel much? - Nope! Air is a bad transfer agent for heat.
(Don't really do this!!!!) If you stuck your hand in the slurry, it would instantly freeze your skin, and do some serious damage in a few seconds. Liquid rapidly and efficiently transfers heat.

Why,because there is no such thing as transferring the cold. It is the heat that is absorbed from the blade.
 
In my experience, D2 responds best to a relatively rapid quench, all the way to Mf (-100). I recommend a good plate quench, then dry ice, before tempering. You want to avoid any delay finishing the quench to minimize RA. I have looked for and found no improvement to cryo temperatures beyond what you can get with dry ice.
 
Nathan the Machinist said:
In my experience, D2 responds best to a relatively rapid quench, all the way to Mf (-100). I recommend a good plate quench, then dry ice, before tempering. You want to avoid any delay finishing the quench to minimize RA. I have looked for and found no improvement to cryo temperatures beyond what you can get with dry ice.
Click to expand...

+1
Stan
 
Responders, thank you. Next, since I live in rural Illinois, dry ice is not readily available. So, can I remove the blade from the ht oven, plate quench to room temp, and put on the shelf until I can aquire the necessary dry ice to complete the process?
Thanks again.
'cacci
 
Not really. Retained austenite stabilizes at room temp. The longer the wait, the more permanent the RA becomes.

That said, there is no real need for cryo or sub-zero if you don't have it readily available. You won't notice any real difference in the blade's performance. The hardness might be a point less than if you did cryo, but with dry ice, there may not even be a difference. RA gets a big Bogyman reputation, but in many parts of the industry, a little RA is a good thing. It increases the toughness a bit.

Now, how much RA are we really talking about here. In my best guess, I would say 3% max....probably only 1%....so if you don't want to do a sub-zero/cryo then just temper twice after bringing the blade down to room temp from the plate or oil quench. Don't even think twice that your blade won't be as good as you could ask for.
 
bladsmth,
Thanks for the concise and specific response. Until I'm convinced by someone that the end result is a lot more significant than you've described, I'll continue without subzero.
You guys have all been great in your assistance.
'cacci
 
bladsmth said:
there is no real need for cryo or sub-zero if you don't have it readily available. You won't notice any real difference in the blade's performance.
Click to expand...

Have you done this? Do you know this for a fact?

bladsmth said:
Now, how much RA are we really talking about here. In my best guess, I would say 3% max....probably only 1%....so if you don't want to do a sub-zero/cryo then just temper twice after bringing the blade down to room temp from the plate or oil quench.
Click to expand...

You'll be doing very well to get under 5%. Current literature gives more like 20%. The texts have changed, the old information was inaccurate.

bladsmth said:
Don't even think twice that your blade won't be as good as you could ask for.
Click to expand...

Don't even think twice?

'cacci said:
bladsmth,
Until I'm convinced by someone that the end result is a lot more significant than you've described, I'll continue without subzero.
'cacci
Click to expand...


If you don't care enough about what you're doing to do a little research for yourself, why would you expect someone else to do the convincing for you. Knock yourself out. I've wasted too much of my time here trying to illuminate a very common problem with a very simple fix, and I'm done with it.
 
Cacci

Nathan has done extensive testing and research with D-2 and cyro and sub zero quench . He has also documented it here on the forums with his test to show the results and differences . You may be able to search and find it . Cyro does help .

As Stacy said , with out it you will still have a good blade but as Nathan said , it will not be all it can be .
 
A while back I posted in a thread, kind of a put up or shut up deal. Nathan was the only one to step up and send me a blade. I put it through the paces and was impressed. I tested against one of my own blades in D-2. Long story short I tweaked my recipe.
Yes D-2 is a damn fine blade steel. And will make a good knife with standard heat treat.
Yes D-2 is a better blade steel with reduced RA.....achieved through sub-zero or cryo.
Nathan, Thanks for all you have done and please don't be discouraged by ignorance and negativity. I know your background as it resembles mine, most guy's just don't have the experience with tool steels to make statements on the subject. People, you can read the literature and quote it all day, but until you test it yourself please don't comment.
 
Nathan, I greatly appreciate your input and advise. You have done real testing with comparative results that I and most others have not. I certainly yield to your info over mine.

Don't even think twice that your blade won't be as good as you could ask for.

I agree that this isn't well worded. What I meant was the the blade will still be functional for most all cutting tasks.

I do a sub-zero on most stainless blades, and have cryo done when sent out in batches. I have also done D-2 without either, and the blades worked and cut just fine.

I totally agree that it is best to do it if one can. What I was trying to say was that if doing a home HT on D-2 and neither was available, it won't ruin the blade.
 
I agree with the folks that sub zero or cryo as part of the quench (immediatly after frozen plate quenching)
Then do the draws. Most high alloy knives will be ok without the sub zero, cryo quench, D2 not so much.
Theres not too many out there where a freeze isn't recommended. Do I really think I know more than the
people making the steel?- NOT.
Ken.
 
Most of the hunting knives I make are D2. Many have gone to friends and their friend and one of them does wild game processing commercially, so I get feed back. I also have cut up stuff, peeled metal and even broke a few. I have never gathered any hard data to support my belief that the subzero helps, but, I hardness test every one after plate quench before subzero and after, then after 1 and 2nd temper. I gain a good point of RC. Although I believe you can make a good D2 knife without the subzero, I firmly believe you are leaveing something easy to get on the table. I usually do 5 at a time. A trip to the grocery store for some dry ice while the blades soak in the oven. Mix 4 or 5# slowly into about 3 gallons of kerosene (It will "boil" over if added to fast) After the plate quench remove from foil packets and finish cooling in tap water, shake dry and into the dry ice slurry for 1/2 hour while the tempering oven comes up to 400f then quick wash with soapy water and into the temper. after 2 hours I go back into the dry ice slurry I have added a bit more dry ice to for a second little soak then wash and back to the oven at about 440f. Get between right at 61RC.

D2 won't get so sharp that hair falls off at the sight of the edge, but, it will stay easy hair shaving sharp for a long time. I warn every one it is not for prying, but if your going to pry with a knife and break D2 you would probably also keep prying hard enough to break say cpm154. Not many good thin tips are going to let you go very far at 61 RC. If you want to pry get 5160 or the like.
 
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