Liquid nitrogen

mete said:
Proper HT + LN bonus.
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Mete (or anyone)

I think I am getting somewhere around 63/64 Rc with fully hardened 52100....I temper it back until I am hitting 59/60 which suits my blades....I do not want a harder edge on the finished blade...........so would I gain any advantages from LN, even though I would want to draw it back to the 59/60 Rc level..is there something I am missing?

thanks
 
Kevin , there you're looking just at hardness.You have to do a little experimenting to compare toughness, wear resistance etc they're all part of blade characteristics that shoul;d be looked at.
 
Mete said: "Proper HT + LN bonus".

I've been working with 5160 and 52100 lately, and want to make the very best blade I can, using information I've learned from many sources, most of which were on the forums. It seems that I need to put a Dewar on my list of "Ebay stuff" to watch for (for the 52100)
 
mete said:
Kevin , there you're looking just at hardness.You have to do a little experimenting to compare toughness, wear resistance etc they're all part of blade characteristics that shoul;d be looked at.
Click to expand...




Its my own experimenting with regards to toughness and wear resistance (and sharpening) which made me arrive at the Rc hardness I currently use....not the other way around.

This is a great thread and one that I am learning from.......but I guess I need to take the plunge and get hold of a Dewar and LN to satisfy my own curiosity.


:)
 
rhrocker said:
Mete said: "Proper HT + LN bonus".

I've been working with 5160 and 52100 lately, and want to make the very best blade I can, using information I've learned from many sources, most of which were on the forums. It seems that I need to put a Dewar on my list of "Ebay stuff" to watch for (for the 52100)
Click to expand...


Robert,
5160 will benefit from LN as well.

Craig
 
Thanks Craig. Time to get set up and find a source of the stuff, probably in San Antonio. Appreciate the help. I assume keep it submerged around 4 hours or so?
 
I can't find it now but IIRC Crucible recommends 8 hours for cryo.
 
Mete: I dunk, introducing the blades slowly into the LN2, hanging on nylon strings. No particular need to use nylon, it's just what I have. I leave them suspended for at least 8 hours, but I like 12 or even 24, too. Longer certainly doesn't hurt, and I leave them in until I am ready to temper them after they warm up to RT.
I believe most of the "slow up, slow down" processing is aimed at eliminating thermal stresses caused by treating larger, more massive, complex parts, like engine blocks, etc.
 
RJ, glad you wrote this! I was thinking that th LN came after the temper. Boy was I in for a treat!

BTW, what's a good size for a Dewar? There are several on Ebay.
 
The cryo converts retained austenite to UNTEMPERED martensite .Always temper after cryo !!
 
Mete, I'm wondering now about the time delay factor. It's been mentioned that the tempering should take place very soon after HT. So now, are you saying that the LN should take place very soon after HT, then temper soon also? I want to be sure I have this right, even though I'm not set up yet.
 
I'm getting ready to start Cryo too. I have a few blades thats already tempered. What if i wanted to cryo them, could I cryo and do another tempering to them?
 
Since there seems to be some confusion let's start at square #1. After you quench the steel you can either go directly to cryo or for less of a risk of cracking 'snap temper' which is a 300-350F temper .Then go to cryo. Tempering at 400F or higher will stabilize the retained austenite preventing transformation of the RA. After cryo I would let it come to room temperature then temper twice ,2 hours each,at 400F or higher depending final hardness desired ....Apparently most of you dunk and it wouldn't hurt the blade to slowly introduce the blade to the LN.
 
You can cryo at any point and see improvement. I used to cryo after the first temper. Then, I switched over to the snap temper before cryo. Now, I cryo immediately after quench and it works fine for me. Yes, you must temper after cryo.
If you have access to a hardness tester, you can learn a lot about your HT process by testing before and after cryo.
 
rj martin said:
You can cryo at any point and see improvement. I used to cryo after the first temper. Then, I switched over to the snap temper before cryo. Now, I cryo immediately after quench and it works fine for me. Yes, you must temper after cryo.
If you have access to a hardness tester, you can learn a lot about your HT process by testing before and after cryo.
Click to expand...

RJ I have a tester so keeping notes along the way won't be a problem. When you say that you "cryo immediately after quench" I assume you mean let it get to room temp first then cryo?
 
Robert: Yes, you are going for continuous cooling. If you want to extend your LN2 supply, you can put the blades in your freezer first, for, say 20-30 min, then into the LN2. It is surprising how much LN2 boils off at the start. Having somewhat cold blades to start with helps.
 
I have and use a lab Dewar ( not so insulated as a regular dewar)
it's holds 8.5-9 pounds of LN full,
so it will boil off in just over 20 hours so if I leave my blades in until it's all boiled off and wait another few hours it gets a slow warm up to room temp then off to the temper.. this saves me some worries about warm up stresses..
 
Dan, would there be a concern that the upper part of your blade is not getting the same amount of time in the LN, as the lower part? I'm not being a wise a--, but I got to thinking that the tip (if down) may be in the drink several hours longer for instance.
 
rhrocker said:
Dan, would there be a concern that the upper part of your blade is not getting the same amount of time in the LN, as the lower part? I'm not being a wise a--, but I got to thinking that the tip (if down) may be in the drink several hours longer for instance.
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no problem Robert
the depth of the LN in my dewar is like 15" at about 9 pounds
it's still very cold just above the LN as it boils off and still well with in the cold needed, But I'm getting I'd say about 9-10 hours full dunk on the edge of an 8" blade, :)
 
rj martin said:
I believe most of the "slow up, slow down" processing is aimed at eliminating thermal stresses caused by treating larger, more massive, complex parts, like engine blocks, etc.
Click to expand...
Probably also uses less LN, as you use the cold vapors to cool the metal as well. If you have cold vapor coming out you're wasting cooling capacity. This would be important in an industrial process.
 
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