Sub-zero vs. Cryo

WaltE99

WaltE99

Fickle Bastard Blades
Joined
Oct 5, 2015
Messages
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Which of the following steels need Cryo and which are OK with sub-zero?

AEB-L
Nitro-V
440C
CPM 154CM
S 30V
S 35VN

Thanks!
 
All are ok with sub zero, all are better with cryo. Sub zero will get you to Mf,cryo will form eta carbides resulting in better toughness.
 
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Whole heatedly agree with Stan....I Cryo all Stainless since I have the ability. Word on the street is AEB-L performs better with Sub-Zero which is another reason AEB-L is popular for beginners.
 
According to the B-U rep at Blade a few years back, Elmax, M390, etc "need" cryo as dry ice is not quite cold enough. I would guess that similar alloys from Crucible, etc would be the same.
 
"Need" is not quite the right word. As far as I know the Mf of all steel is reached by -100°F. What the drop to -350°F does is start the creation of eta carbides and add a point more hardness.
 
I believe Larrin already clarified about all of these. Both subzero and cryo will bring the steel to lower Mf point thus more RA conversion = higher HRC. Cryogenic when soak long enough will lead to precipitation of ETA carbide when tempering.

But keep in mind RA is not always a bad thing since it improve overall toughness of steel. Hard to believe but many world class maker do their HT on various of high alloy steel without any freeze treatment at all. To name a few, Jason Stout, Burchtree, Tom Krein, Dozier and many more.

However, I prefer to do subzero on any of my work piece tho because I know if I were a customer I would want to have it make to the best as possible.
 
I am going by what the manufacturer's rep said. I asked him because they had a chart at their booth that appeared to indicate that you needed a lower temp. It didn't say -350, but it did say like -130 F or so. IIRC, Dry ice slurry would have been like 25-30F short.
Stacy E. Apelt - Bladesmith said:
"Need" is not quite the right word. As far as I know the Mf of all steel is reached by -100°F. What the drop to -350°F does is start the creation of eta carbides and add a point more hardness.
Click to expand...
 
As far as I understand it, some of the steels that have a LOT of alloying will not even begin to reach Mf with sub zero. And some have so much alloying that cryo (LN2) isn't cold enough for Mf, and the only way to get rid of it (RA) is the secondary hardening tempers. Steels that aren't often used in knives, however, like T15 come to mind. I don't have any immediate resource to verify that, so take that for what it's worth. About 2 pesos.

And about some RA being a good thing in steels, I'm still not sold on that. Again, to my current understanding, if RA is present in a steel and then is subject to shock (impact), the RA in that localized area is immediately transformed to untempered martensite. For my money, the goal is as much RA reduction as is reasonable (get as much martensite conversion as is reasonable), and then temper.
 
There was some testing done a while back that indicated some of the steels listed hold their edge better without cryogenic treatment. It may be worth trying some without either treatment.
 
For me, there's no point to dry ice. I have to drive 45 miles to get either dry ice or LN. A $200 10L chinese dewar costs me a little over $20 to fill and keeps for almost 3 months. Dry ice, I don't actually know what it costs per pound, because I would have to drive and get it every time I was heat treating, so no matter how inexpensive it is, if I have to make even 2 trips in 3 months, vs 1, they could give it away and it would be more expensive to me.

Just something to think about. A dewar seems like a chunk of change, but it paid for itself for me. If you have dry ice around the corner, that may be different.
 
That’s not a bad price. I pay a tad over $60 to fill my 20L. And that’s cheep compared what my argon costs $80
 
Thanks all! Great info. Trying to understand those charts is like trying to jump on a rocket ship when it's already half way to the Intl. Space Station;) I'm going back to read the entire thread, though to see if that helps.

So let's say I go ahead and do Cryo now, what size dewar would I need. Right now the biggest thing I make is a chef's knife OAL 13". Probably will do some choppers at some point, but doubt they would get too much longer than that.

Thanks again,
Walt
 
General rule of thumb is the larger the opening of the mouth the faster you loose liquid nitrogen. So with the price some places charge for this liquid gold I would pick a dewar that fits most of your work and if you need to go larger you can allways pour a little out into a flask. For me I did a bunch of research befor I bought mine and I’m glad I did. My dewar has an evaporation rate of .09L a day so my 20L lasts me 220 days. Now that’s if you don’t disturb or use it. So just keep an eye on the everopation rate and what the size of the mouth
 
Length can be an issue but width of the mouth and blade width seems to be the biggest issue especially with kitchen knives. My neck is 1.9" if I could have a 2.5" for the same money I'd buy it but the ones like JT's are hens teeth on the used market and expensive new or used. Mine does 95% of what I need and I outsource what I can't do. Or pour some LN into a big cooler. You'll lose it of course but that's cheaper than outsourcing the entire ht.
 
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