Cryo, and sourcing LN2

fitzo

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I mean, martensite finish varies so much between the different alloys, but more importantly the different austenizing temps used. Especially if I'm interested in reaching higher hardnesses without going into the secondary hardening range. It can just be difficult to find the information charted out for some steels giving the mf for the different austenizing temps. Well, if it isn't difficult, I just don't know where to look to easily find them.
After thinking about it for a moment, the sure way to go if one has the bux and the access is the cryo/LN route. Then it doesn’t matter what the Mf is, as you’re not going to achieve any colder at home unless you live in a physics lab.

Those who can’t access or aren’t interested in the expense but want to do cold treatment with dry ice can choose their steels accordingly out of what is known scientifically.
 

Blankblank

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After thinking about it for a moment, the sure way to go if one has the bux and the access is the cryo/LN route. Then it doesn’t matter what the Mf is, as you’re not going to achieve any colder at home unless you live in a physics lab.

Those who can’t access or aren’t interested in the expense but want to do cold treatment with dry ice can choose their steels accordingly out of what is known scientifically.
I think the cryo is going to end up being cheaper, but the initial money spent on the dewar is was can be disuading.

You're definitely right about checking to make sure that your particular heat treat reginmen will work well with the equipment one is working with.
 
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I think the cryo is going to end up being cheaper, but the initial money spent on the dewar is was can be disuading.

You're definitely right about checking to make sure that your particular heat treat reginmen will work well with the equipment one is working with.
If you are thinking going full scale cryo, take your time and look on Craigslist, Facebook marketplace, scientific or gov auctions. I found my Dewar on Craigslist from a lab going out of business and holding an auction. It was like $120, as long as the shells vacuum is still good (which can be hard to determine and a gamble) used ones are fine and much cheaper.
 

fitzo

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If you live where there are large corporations involved in science, university labs, etc., check to see if they have a "scientific salvage" open to the public. It's amazing what gets cashiered rather than redeploying used items to another department, project, etc. I got my vacuum pump, 30L Dewar, hot plate/stirrer from my old company's salvage. All like new.
 

Blankblank

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Man. So i went to get the my Dewar filled, and I tried airgas first, just out of convenience. They wanted $9 a liter!!! Didn't even take me a second to turn that down.

I guess I'll need to shop around more. I'm definitely going to check out the place that was recommended in this thread.
 

Blankblank

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Oh. I do have a question.

Does anyone have a recommendation on how to dip larger blades? Ones that are a bit too wide to fit in the Dewar without boiling off too large of an amount of excess liquid nitrogen? My first thought is some kind of smallish styrofoam cooler. Maybe precool it with ice (as much as I can), pour in the amount of ln2 I need dip the blades, and pour whatever is left back into the Dewar.

Obviously not super efficient, but I mean it's the best work around of tall kitchen knives I've thought of so far.
 
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My first thought is some kind of smallish styrofoam cooler. Maybe precool it with ice (as much as I can), pour in the amount of ln2 I need dip the blades, and pour whatever is left back into the Dewar.
That's pretty much accepted as a way to do wider blades. I've sorta started limiting my blades to <2" so they will fit thru the 50mm opening.
 

fitzo

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B Blankblank You can put together a wide cylinder from PVC pipe, a glued/sealed endcap, an unglued endcap, and a flange to set it all in. Wrap it all in rubber pipe insulator and you've got a temporary LN2 vessel. Weight the bottom; you don't want an accidental shoe full.

Don’t seal it tight with LN in it! (Sorry to state the obvious.)

Ps Airgas sucks, here, too. The local welding shop is much better.
 
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J. Hoffman

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If you can prevent submerging the blades in the LN, it will last longer. I have a 47l and the first half gasses off much quicker than the second half because the blades are not submerged and just suspended above.
 
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Blankblank

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If you can prevent submerging the blades in the LN, it will last longer. I have a 47l and the first half gasses off much quicker than the second have because the blades are not submerged and just suspended above.
That's probably good enough for most steels. depending on the alloy, and what I'm trying to achieve I can try that. I can't remember how cold it is above the ln2 but I do remember that it's not as cold as the ln2 itself.
 

Blankblank

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B Blankblank You can put together a wide cylinder from PVC pipe, a glued/sealed endcap, an unglued endcap, and a flange to set it all in. Wrap it all in rubber pipe insulator and you've got a temporary LN2 vessel. Weight the bottom; you don't want an accidental shoe full.

Don’t seal it tight with LN in it! (Sorry to state the obvious.)

Ps Airgas sucks, here, too. The local welding shop is much better.
Good idea. Ill look into making one.
 
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That's probably good enough for most steels. depending on the alloy, and what I'm trying to achieve I can try that. I can't remember how cold it is above the ln2 but I do remember that it's not as cold as the ln2 itself.
You might wish to check the temperature of the vapor space above the LN. I did that a yr or so back and "IF" I remember correctly the vapor space was about the same temp as LN.
 

J. Hoffman

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The vapor space above the LN (in a dewar) is plenty cold enough. I got that info from someone who ships millions of dollars of semen in one dewar overseas. I trust he's done his homework when it comes to how cold the vapor is. I've confirmed that with other people I trust. I unfortunately don't have any way of testing those types of temperatures.
 

Blankblank

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This is the number I was thinking of when I made that comment.

Screenshot_20220930-195521.png

If you think of it, it's not physically possible for the vapor above the liquid nitrogen to be as cold as the liquid nitrogen, if it was warm enough to not be liquid anymore, and oxygen turns to liquid at a warmer temp than nitrogen, so its not oxygen that hasn't reached ln2 temps either.

Not saying that's not cold enough to heat treat most steels. Just its not as cold as the liquid.
 

Stacy E. Apelt - Bladesmith

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That article points out something I read elsewhere. Many welding suppliers sell pelletized dry ice by the pound. You can put half fill a Dewar and the temp will stay right at -90°F for a long time. The blades can be suspended in the Dewar, or you can pour out the amount of pellets you need to make a dry ice and alcohol slurry.
-90°F is sufficient for all steels to reach the Mf as far as I know. Cryo does other things, but the steel will reach final martensite conversion at -90F. It would be easy to give additional cold treatments between tempers, too. The time at -90F would only need to be a few minutes (to allow the blade to drop to the Dewar internal temp), as there is no advantage to long soaks. Once you reach the Mf you are there.
 
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