Cryo Treat Help

Outdoor Gear Dad

Outdoor Gear Dad

Joined
Jun 1, 2019
Messages
211
Hello Blade Forum. So for context I am new to making blades but it’s quickly became an obsession. I have made several dozen knives and with each one they are drastically improving. I just purchased a even heat kiln and am awaiting its arrival. I’m really into the a science part of the process and have been reading all about cryo treating. So here is my question. I need a LN dewar....since this is just a side hobby that is funding itself, any inexpensive options people can recommend for the hobby blade maker?

Also, how often do I need to replace the LN? I imagine with time and after submerging blades it eventually looses its temperature. Am I wrong?

Also how long do you soak a blade in LN for? Thanks a ton
 
It's unfortunate there are NO inexpensive options when it comes to Dewars. Of primary concern is the "Mouth" opening if you intend to do Blades widths up to including 2" like Kitchen Knives or Wide Blade Choppers. The single most inexpensive way to Chill Blades (not cryogenic) is the use of Dry Ice and Denatured Alcohol However it will not reach the temperatures of Cryogenics.

Initially you should research the dry ice/alcohol method which works well on AEB-L...Other Higher Alloys may Require a much Lower Kelvin Temperature(-300)....

Liquid Nitrogen LN2 is a Liquid that wants to become a Gas Rapidly when exposed to Atmosphere which is the Reason For a DEWAR.
There are conflicting numbers when it comes to how long the LN2 will last in a dewar based on evaporation rate listed by the manufacturer. The better the Quality of Dewar, Foam Plug and Diameter of the Mouth all play a role in how long the LN2 will last. I have a 30L VWR that cost a fortune, but in the long run based on my operations "Batches" of 30-50 blades at a time works very well. The LN2 does not Lose Temperature it EVAPORATES and Should NOT be capped tight because as a Gas it Expands and would explode the vessel. I'm not sure of what the smallest Dewar capacity with a 2" mouth is maybe 10L but you can fill half way for a savings and depending on how many blades you need to Cryo...You can Research individual Steels for Heat Treat Cryo information they can be different from one to another...Hope this helps
 
Busto said:
It's unfortunate there are NO inexpensive options when it comes to Dewars. Of primary concern is the "Mouth" opening if you intend to do Blades widths up to including 2" like Kitchen Knives or Wide Blade Choppers. The single most inexpensive way to Chill Blades (not cryogenic) is the use of Dry Ice and Denatured Alcohol However it will not reach the temperatures of Cryogenics.

Initially you should research the dry ice/alcohol method which works well on AEB-L...Other Higher Alloys may Require a much Lower Kelvin Temperature(-300)....

Liquid Nitrogen LN2 is a Liquid that wants to become a Gas Rapidly when exposed to Atmosphere which is the Reason For a DEWAR.
There are conflicting numbers when it comes to how long the LN2 will last in a dewar based on evaporation rate listed by the manufacturer. The better the Quality of Dewar, Foam Plug and Diameter of the Mouth all play a role in how long the LN2 will last. I have a 30L VWR that cost a fortune, but in the long run based on my operations "Batches" of 30-50 blades at a time works very well. The LN2 does not Lose Temperature it EVAPORATES and Should NOT be capped tight because as a Gas it Expands and would explode the vessel. I'm not sure of what the smallest Dewar capacity with a 2" mouth is maybe 10L but you can fill half way for a savings and depending on how many blades you need to Cryo...You can Research individual Steels for Heat Treat Cryo information they can be different from one to another...Hope this helps
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Helps a ton. I think because this is just a side hobby that makes enough to support itself maybe I just stick to a sub zero treatment with dry ice.
 
The guy who comes to fill my dewar just charges a flat rate for the visit and will fill whatever size dewar you have. So for me it was best to go big.

Might be worth checking your LN supplier before choosing your Dewar.

Also worth knowing is that Dewars can loose their vacuum so beware of something very cheep.
 
Outdoor Gear Dad said:
Helps a ton. I think because this is just a side hobby that makes enough to support itself maybe I just stick to a sub zero treatment with dry ice.
Click to expand...
If you're only making a 3 or 4 knives per mo, you'll find dry ice to be the most economical, and if you're using AEB-L or similar SS dry ice works just as well as LN. What you're looking for the RA conversion. Simple alloys of high carbon steel the RA conversion is complete well above room temperature. AEB-L and the like the conversion will take place around -80F to -95F so dry ice provides that nicely. There are some SS that requires lower temps and do need LN. If you're doing a good number of blades per month you'll find LN most economical.
 
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Busto explained it perfectly. The only thing I'd add is with alot of Stainless Steels the difference in finished quality between dry ice and LN is minimal. Most end users would or never could tell the difference. Like most things in life it's a trade off. For the hobbyist if you have a local access to DI and only making a few knives every now and then I'd go that route. If your in business and making lots of knives then LN is obviously better with a end product that is a couple percent better depending on the steel you are using.
 
Just use Dry ice ad denatured alcohol from Home Depot/Lowes. Three to five pounds of dry ice is plenty. A gallon of alcohol will last for years. Just let the dry ice evaporate and pour the alcohol back in the can. Leave the lid a bit loose overnight and give the can a shake the next day to release any dissolved carbon dioxide .. then cap it back tight.
 
There are affordable Dewars on Amazon around $300 for 10L with 2" openings.

Cost to fill can be $2-5 per litter depending on your location and provider.

LN lasts up to 1-3 months depending on frequency of use.

Soak time varies but 1 hour is a good place.


Outdoor Gear Dad said:
Hello Blade Forum. So for context I am new to making blades but it’s quickly became an obsession. I have made several dozen knives and with each one they are drastically improving. I just purchased a even heat kiln and am awaiting its arrival. I’m really into the a science part of the process and have been reading all about cryo treating. So here is my question. I need a LN dewar....since this is just a side hobby that is funding itself, any inexpensive options people can recommend for the hobby blade maker?

Also, how often do I need to replace the LN? I imagine with time and after submerging blades it eventually looses its temperature. Am I wrong?

Also how long do you soak a blade in LN for? Thanks a ton
Click to expand...
 
Outdoor Gear Dad said:
Hello Blade Forum. So for context I am new to making blades but it’s quickly became an obsession. I have made several dozen knives and with each one they are drastically improving. I just purchased a even heat kiln and am awaiting its arrival. I’m really into the a science part of the process and have been reading all about cryo treating. So here is my question. I need a LN dewar....since this is just a side hobby that is funding itself, any inexpensive options people can recommend for the hobby blade maker?

Also, how often do I need to replace the LN? I imagine with time and after submerging blades it eventually looses its temperature. Am I wrong?

Also how long do you soak a blade in LN for? Thanks a ton
Click to expand...

Have you read these?

- https://knifesteelnerds.com/2018/12/03/cryogenic-part1/
- https://knifesteelnerds.com/2018/12/10/cryogenic-processing-of-steel-part-2/
- https://knifesteelnerds.com/2018/12/17/cryogenic-processing-of-steel-part-3/

I wont even try to summarize those articles....but I got the impression dry ice was enough for me (hobbyist). If you're selling knives; maybe you want LN to make sure your customer is getting the best blade possible, but perfection can be the enemy of good-enough (and your wallet).
 
I used to use dry ice but transitioned to LN just for ease. In Canada, Dry ice is considered a hazardous material (yes I argued with the gas guy that we breath the stuff out) so I can only get it from my gas suppler during working hours which is a pain. With LN, I can have it in the shop and just do a few blade at a time if I want. It'll last about 2.5 months in my 25L Dewar.

If I was in the states where dry ice was readily available I would stick with that as I do almost everything in AEB-L.

One advantage of dry ice is that I tend to heat treat knives in batches. My quench plates heat up so I use the dry ice to cool them off between blades.
 
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