Cryo testing

Daniel,

All you explained makes perfect sense to me. It is not difficult to imagine the stress caused by sudden temperature plunges. I believe your technique, as so far described, is solid. As for me, I will just have to build my procedures as funds, education and time permits - doing the best I can in the times between.

Thank you for sharing.

Roger
 
I'd like to talk about the shock, say O1 steel when dropping
from 1550-1600 deg's
quenched in 130 deg oil this has got to be more shock than
the dipping in LN2 slow as you can by hand..that's less then 400 deg's.in more time..

you can put your hand into LN2 real fast and
the boiling from the heat in your hand causes a barrier protecting your hand... for a short time....protecting the blade too.(for a short time)
don't try this at home guys :eek:
but it just brings up a point that it IMO won't shock as bad as one thinks.:confused: I posted what I did to shock some o1 and I wacked it bad with shock :( :)
 
Not really knowing better because of lack of experience: I would think slow as you can into -300 F. would be much greater shock to adjacent grain than fast as you can.

Quenching to 140 F. from 1500 - 1900 F. - I'm not so sure its a linear experience. I wonder if it is really so simple as just comparing number of degrees of heat but perhaps more important as to where you are on the temperature scale, and that a sudden drop from ambient room temperature to -300 may well be greater in shock than from 1900 to 140. I just wonder. I don't really know yet.

Roger
 
Basic considerations about thermal shock:

The colder temperature is a reflection of slower molecular activity. Hotter temperatures are an indication of greater molecular activity. Steel is easily deformed at hot temperatures, but becomes far more brittle at colder temperatures.

The cold is causing the steel to change, but it is changing very slowly, and also because of the cold it is far more brittle.

When we superimpose our desired quench temperature changes over a typical (not all) TTT curve, we see that the fastest change needs to happen from the austentizing temperature to just below the nose at about 850F. Then the rate could slow down to get past the lower lip at about 400F. Once it is in the Martensitic start range where does the line go? It receeds way back.

Now let's graph out the cryo (eliminating tempers). We can cool the steel down to -120F at 4 degrees a minute, but from there to -300F the MAX is 1 degree a minute.

It might help to think of the whole range of temperature change from austentizing to deep cryo as a parabolic curve. It is almost vertical at the beginning and almost horizontal at the end.

Daniel
 
A couple of different thoughts.

Let me begin by offering a free cryo to anyone on this list for the next 2 weeks. All you pay is shipping both ways. If you like the results use my service again.

Next:
Would any other knifemakers like to participate in a test by doing 3 identical pieces? This would insure a variety of steels, grinding styles, etc.

Daniel
 
Graymaker makes a very good point. The amount of change occuring within steel from austenitic to martensitic ranges upon a quench and the speed and volatility in which it occurs is horrendous, in comparison to the kinds of stresses that arise from simply dipping hand warm steel into LN2 as opposed to gradual cool down. I feel there is nothing inherently wrong with "dipping" blades and there is no reason cracking would occur "just because it was dipped". It has to be looked at subjectively. Prior HT will determine whether or not your steel is going to crack in cryo or any other subsequent treatment. So, if you have a steel with an unusually high amount of retained austenite and/or the part dimensions are greatly different in thickness, a "dip" is probably gonna give you hell. However, a good quench, with a little retained austenite and simple, similiar part dimensions (i.e. knife blades) you'll be just fine. Checks and balances. Just like, "what is the best quenchant?" :cool:

I'm not trying to step on toes, in fact, I use a gradual cool down. But that's more because of the nature of my quench and cryo than intention to a avoid a "dip".

Jason
 
I buy into Daniel's explainations 100 percent even though I'll be slamming my steel right into the LN, but only because I don't have the capability to do it otherwise - yet.

Roger
 
Originally posted by knightsteel


There is also a paper done at Jassy Polytech in Romania that I have not yet located.
Click to expand...

If you have the name of that paper I might be able to get it for you.
 
Flava,

I do not have the name of the study, but it was done by Dr. Joan Alexzndru and Dr. Constantine Picos of The Polytechnic Institute of Jassy, Romainia.

Any assistance would be appreciated.

Daniel
 
Guys - to boil the whole thing down ALL YOU GOT TO DO is use common horse sense. Knightsteel is right as a rabbit. Stats are great but the common sense is right there for us all to see and know to be correct. The picture is right there in front of all us to see. The man is correct in what he says. I buy it and if you don't grasp thermal shock. It's easy. Can't you see it???

Roger

EDIT: The man is right in his explanation of theory. Period. I will bet my best work on it.

I feel I have learned from him and I noticed the best of us (I do not include this newbie) has not argued one bit against his experience.

I love all you guys and sure hope I do not cause dandruff to fly. However, I am confident beyond doubt that his theory is based in solid foundation.
 
Graymaker, Epsilon,

You make valid points.

With cryo dipping you are still gaining the conversion of retained austenite and the precipitation of fine carbides. But thermal shock is a known factor. You lose some toughness.

How critical is that based on steel choice, prior HT, design, and intended use? The greater hardness and wear resistance may very well make up for it. For many knives this may be an acceptable trade off.

But the process outlined in this thread seems to yield far greater toughness while retaining the other benefits.

Daniel
 
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