At Home Cryo?

colu41

colu41

Joined
Dec 24, 2014
Messages
1,598
After I finish building my oven, I will need a way to cryo treat my blades. As I would rather not have to send them out. Whats the easiest way of doing this?
Dry ice is kind of the backyard way of doing it I've read. But it seems unless you're doing a bunch of blades at once, it would kind of be a waste.
I'm not a production knifemaker so I don't like starting 5-10+ blades at a time. It makes me feel overwhelmed for some dumb reason but, either way, I usually only have 1 or 2 going at a time.

Also, how extensive of a setup is needed for liquid nitrogen?
 
A dewar is all you need. I bought one off fleabay for like $300 or so and it cost $30-$60 to fill it. Last about 4-5 weeks.
 
Check Craigslist often for dewars. I have seen a couple around my area for $100. That said, I have been using a dry ice slurry for my knives anyhow.
 
I read somewhere that there is no difference using liquid nitrogen vs dry ice slurry as far as the end product goes from a metallurgical point of view. Can't remember where it was. I know for AEB-L dry ice slurry is fine and the PDF that I read from Crucible Industries regarding S35VN uses -112F for their recommended freezing treatment. I think that temp is achievable with dry ice/acetone.
http://www.crucible.com/PDFs\DataSheets2010\dsS35VNrev12010.pdf
 
Lo/Rez said:
I read somewhere that there is no difference using liquid nitrogen vs dry ice slurry as far as the end product goes from a metallurgical point of view. Can't remember where it was. I know for AEB-L dry ice slurry is fine and the PDF that I read from Crucible Industries regarding S35VN uses -112F for their recommended freezing treatment. I think that temp is achievable with dry ice/acetone.
http://www.crucible.com/PDFs\DataSheets2010\dsS35VNrev12010.pdf
Click to expand...

Thats nice to hear. I plan on using s30v or s35vn.
 
A dry ice slurry will get most of your retained austenite converted. A LN cryo will do the same and yield some extra carbide formation in appropriate steels.

I bought a second hand high quality dewar years ago. It's a large one and costs me more to fill up but will hold a fill for about two months.

--nathan
 
I use mainly AEB-L steel. I've only used dry ice for the sub zero quench. Per the recommendation of someone on this forum I stopped using the slurry and now just powder the dry ice and pack it around my blades. I've not noticed a difference between the two processes in the resulting hardness, as I've tested on my hardness tester. Although I guess hardness wouldn't necessarily tell the whole story. Per Sandvik's data sheet the steel just has to reach -95, no soak required. Seems like the powdered dry ice should do that. Anyone have thoughts on that?
 
extdrive said:
I use mainly AEB-L steel. I've only used dry ice for the sub zero quench. Per the recommendation of someone on this forum I stopped using the slurry and now just powder the dry ice and pack it around my blades. I've not noticed a difference between the two processes in the resulting hardness, as I've tested on my hardness tester. Although I guess hardness wouldn't necessarily tell the whole story. Per Sandvik's data sheet the steel just has to reach -95, no soak required. Seems like the powdered dry ice should do that. Anyone have thoughts on that?
Click to expand...

Pretty sure on another thread Stacy said that the powder is not as good because it doesn't have 100% contact with the blade and that the air pockets around the steel don't conduct the temp very well to the steel.

I'm about to start working with stainless (have only used high carbon so far) and from what I have read most stainless is fine with dry ice slurry. On S90V I believe, it needs to get colder than the dry ice can get so it needs the full LN.
 
Powder dry ice will NOT reach the same temperature as a dry ice slurry - just a fact. Put a thermometer in and check it.

Denatured alcohol is about as good as anything to use - less of a mess than acetone. Once the dry ice goes away, just pour the denatured alcohol back in container for next time.
 
The final blade will be basically identical with either method.

The simplest and best method to finish the quench ( that is what the sub-zero or cryo treatment is for) with high alloy steels is a dry ice slurry. I use methanol and broken up dry ice. The approx. 5# of dry ice costs about $5-10 and the alcohol ( about $10 a gallon) is reusable dozens of times. A slurry batch lasts a couple hours. A Dewar and LN are somewhat better for a few steels, but will cost a lot more per blade unless you do large batches on a continuous yearly output.

A suitable Dewar for knife use runs between $200-400 and it will cost about $50-70 per month to keep it full. Well worth it if you do several hundred knives a year, not so good if you do 5 a month.

All that said, you can't do a better HT on most all stainless steels that you will get from Peter's. You almost certainly can't do it as cheaply.
 
Ken H> said:
Powder dry ice will NOT reach the same temperature as a dry ice slurry - just a fact. Put a thermometer in and check it.

Denatured alcohol is about as good as anything to use - less of a mess than acetone. Once the dry ice goes away, just pour the denatured alcohol back in container for next time.
Click to expand...

If I had a thermometer that went all the way down to -109 I would have. Sounds like you have tested it though? Does it make it to -95? That's all I need for AEB-L.
 
Gas is a poor heat transfer medium. Powdered dry ice, no matter how tight you pack it around the blade, is still transferring the heat from the blade to the dry ice through a layer of gas. It will eventually get low enough, but may be uneven in doing so. There is a potential for warp and uneven hardness.

A slurry uses liquid alcohol/acetone/antifreeze as the transfer medium. This is a very efficient medium, and the transfer of heat is rapid and even.
 
Stacy E. Apelt - Bladesmith said:
A suitable Dewar for knife use runs between $200-400 and it will cost about $50-70 per month to keep it full.
Click to expand...

Huh?

I have a 35 liter dewar. It costs me $60 to fill, and I get 3 MONTHS out of it, give or take depending upon how many knives I make and treat. Last fill up lasted almost four months.

Many steels require cold treatments colder than -95. Check your documentation, and make certain which is right for your needs.

Seems like many are willing to dismiss eta carbide formation as a necessary function of heat treatment. If it makes for a better knife, I'm doing it. I think I owe it to my customers.
 
I bought a junk Dewar for $20. It holds liquid for 1.5 days, which is plenty of time for me to do my HT. I do batches of steel, and will do several blades at once. I only need liquid once every two months or so. I'm fortunate to have the worlds largest consumer of LN in my home town. They waste more liquid everyday than I'll use in a lifetime. They will fill my dewar 4-5 times for $20.
 
Metallurgically there is a significant difference between sub-zero [ ~ -100 F ]and cryo [liquid ntrogen ] [ - 300 F ]. If you can't get LN then use a lesser steel , there are some very good ones out there !
 
Matthew Gregory said:
Huh?

I have a 35 liter dewar. It costs me $60 to fill, and I get 3 MONTHS out of it, give or take depending upon how many knives I make and treat. Last fill up lasted almost four months.

Many steels require cold treatments colder than -95. Check your documentation, and make certain which is right for your needs.

Seems like many are willing to dismiss eta carbide formation as a necessary function of heat treatment.
Click to expand...
Excellent post with great information. Our experience matches yours. A dewar refill is 3-4 months.

Matthew Gregory said:
If it makes for a better knife, I'm doing it. I think I owe it to my customers.
Click to expand...
I don't think this can be stressed enough. In my opinion, this is the point of buying a custom knife.

Chuck
 
I was going by the smaller 10L Dewars that people often use. They seem to only last a month or so. YMMV. In either case, the Dewar and the LN refills are far more cost than $5 of dry ice and a gallon of hardware store alcohol.

The basic comment I was making was that by -100F the steel has fully hardened and converted into 100% martensite ( or as much as it will get) at -100F. There are eta carbides and other things changed in cryo, but they do not make more martensite. For the hobbyist home heat treater, sub zero is completely sufficient. Obviously a professional HT shop or full time maker who sells knives for a living will go with Ln and cryo.

From what I have read, there is some dispute among makers and metallurgists as to how much of the eta carbide changes survive the tempering. Personally, I doubt anyone but a metallurgical lab could tell whether it had cyro or just sub-zero.

All of the above is why I stress the value of a professional HT from Peter's (or some other experienced knife HT professional).... where they have the right equipment and know how to use it.
 
You must log in or register to reply here.
Back
Top