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Liquid nitrogen


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This might sound a bit steep beforehand but maybe it isn't.

 

I work a lot with liquid nitrogen at work and that got me thinking. Has anyone tried hardening a blade in it?

 

At first you might think "-192 degrees celcius thats impossible!" but is it? My experience is that the cooling capacity is quite low, even a small sample takes quite a lot of time to freeze. You can stick your hand in it if you do it quickly without feeling the cold, and yes I tried it, being curious is probably a bad thing in my case. A few reasons why I think it might work:

-The cooling capacity is quite low as I said. The cooling rate might even be very close to water especially if the metal is still hot since a lot of the gas will boil off, and I mean a LOT (white mist everywhere). With the added benefit that you won't get bubble nucleation on the blade, which I've heard could cause unwanted stress points during hardening, since the liquid will only touch the actual blade if its cooled to low temperatures.

-It forms a insulating layer of gaseous nitrogen, this gives a very homogenious cooling which prevents cracking and wharping.

-It might even slightly nitride your edge for extra hardness.

 

Has anyone here actually tried it?

For though all creatures under heaven are the products of Being,

Being itself is the product of Not-being.

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From what I understand liquid Nitrogen is actually used on steel that has already quenched in other medias such as water, oil or salt and tempered. When the steel is cooled to really, really cold temperatures the retained austenite(austenite that is not transformed to martensite in the quench) is transformed to martensite. This is commonly done on high alloy steels like 440C, but can also be done with low alloy steels like O1, L6 and 52100, and will result in a few extra points of hardness.

 

As for quenching directly in L Ni, I don't think there a point even if it doesn't end in CATASTROPHY, most likely it will just end in a lot of cracked blades.

 

I've never tried any of this myself, this is just what I can remember from reading various blade related publications. Hope someone with a lot more experience and metallurgical knowledge than me will chime in, Howard Clark perhaps...

Edited by Leif S

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I think it would be a big problem, not for the blade, but for the operator. Nitrogen's expansion ratio from solids to gas is quite impressive, and is the basis of all industrial explosives. I do not know what sort of volume change occurs, in terms of the mathematics involved, but I am sure it would be a great deal of gas evolved very quickly. I suspect it would result in a vapor jacket that would cause water hardening steels not to harden at all. All speculation though. I would be willing to watch, from a small distance, with beer in hand... :)

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howard the question is..... what kind of beer would you have in hand ???

All these things shall love do unto you that you may know the secrets of your heart,and in that knowledge become a fragment of Life's heart...

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Nitrogen's expansion ratio from solids to gas is quite impressive, and is the basis of all industrial explosives. I do not know what sort of volume change occurs, in terms of the mathematics involved, but I am sure it would be a great deal of gas evolved very quickly.

 

The solid to gas conversion in explosives you're talking about is a chemical process. Yes liquid nitrogen will produce a LOT of gas but if you do it outside in the wind you probably (heheh probably) won't suffocate. In case of the explosive type of solid-gas conversion you talk about a lot of energy comes from the breaking of the very strong molecular nitrogen-oxygen bond and indeed allso the generation of a lot of gas but it's the chemical bond breaking that makes an explosive explode. With liquid nitrogen you won't have this explosion because you don't have the explosive type bond breaking, it will only cook off very fast instead. This will allso mean a lot of heat is transferred from the blade to the liquid. I'd have no problem sticking a red hot piece of metal in liquid nitrogen, in a very windy place with an oxygen mask that is, maybe I'll be extra nice to my lab-chief so I can take a few litres home sometime. I'm absolutely sure the explosion you talk about won't happen, but the very fast cooking off might be quite spectacular.

 

BTW the liquid to gas conversion is the same for all liquids, the volume changes by a factor of 23 if I remember correctly.

 

I might go for a Grolsch in my hand, I work across from the brewery, in the east off holland it's allmost a crime to drink anything else.

Edited by Sakura

For though all creatures under heaven are the products of Being,

Being itself is the product of Not-being.

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I was not suggesting that it would result in an explosion of the same nature as the breaking of chemical bonds, only that there would be a great deal of gas evolved very rapidly. And yes, I do think the cooking off of the liquid to gas will be spectacular, should you decide to try it.

 

I do still think there will be a vapor jacket problem, but an experiment would resolve that question. :)

 

I favor big malty ales unless it is really hot, then something lighter is in order. Or even a Strongbow when it's hot, if there's one to hand. Mostly I drink coffee in the morning, then tea all the rest of the day. Mostly... ;)

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I'm betting the operator would get differntially hardened, or fully hardened. My blades get treated fine by regular water or quench oil.

 

Dan

Dan Pfanenstiel

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hehe well I might just pass on this one then. I was just curious if anyone here tried it or had the same wharped fantasy about the subject. You'll never know if it works if you don't try it but for now I'll pass on this one. If I do I'll definately tape it, the priceless image of some fool running around in a big steamy mess with a hot metal bar in his hands is probably worth the effort.

 

I'm not that keen on big malty ales Howard. We as Dutch are pilsener type people, if I need something stronger then a Macallan fine oak on the side and a good piece of dried sausage will make me smile the whole night long.

For though all creatures under heaven are the products of Being,

Being itself is the product of Not-being.

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And people say that brine is a harsh quenchant! I would be worried that the temperature in the thin and thick parts of the blade might be a bit much. Could be wrong though. After all I got married three times (sequentially, that is).

 

Doug Lester

HELP...I'm a twenty year old trapped in the body of an old man!!!

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BTW the liquid to gas conversion is the same for all liquids, the volume changes by a factor of 23 if I remember correctly.

 

I just googled and the listed source cited an expansion ratio of 694:1 for LN. Hmmm, Dewar with limited opening, red hot blade, rapid gas expansion... I have a mental image of a carbonated beverage spraying all over everything within range accompanied by a shocked look on someone's face.

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I just googled and the listed source cited an expansion ratio of 694:1 for LN. Hmmm, Dewar with limited opening, red hot blade, rapid gas expansion... I have a mental image of a carbonated beverage spraying all over everything within range accompanied by a shocked look on someone's face.

 

Sorry I was off....I remebered a factor 23 from my study but I got mixed up. I did some searching and one mole (not litre hehe) of gas always gives off 22,4 litres of gas, since avogado's law states that (pressure x volume)/(number of atoms x temperature) is constant. Since a mole of hydrogen weighs 2 grams the one litre to 23 litre rule is quite absurd indeed. How could I be so wrong hehe, it's a scientists thing, so many equations and rules you just cant help mixing them up once eventually.

 

And putting it in a dewar with a small opening is nothing short of suicide, it will blow and completely rip you apart with broken glass schrapnel. I usually use a dewar that has a bowl shape and is completely open at the top side so the rapid expansion won't be dangerous. The mist is pretty harmless. If our main tank pressure valve blows off it gives a LOT of mist but even standing a meter from it you'll only feel a slight cold. As I said before the cooling capacity is quite low, you can actually pour it over your hand without burning it. And it's a very big vessel, 300 litres, it usually fills a 4x4 meter area in thick mist when it does. You can easily breathe standing in it since that gas is so heavy that only a really thick layer will form at ground level. It allways provides a lot of entertainment when new and unsuspecting trainees stand too close. Priceless scaring the new guy on his first day, they got me too three years ago I still vividly remember it.

 

Could be wrong though. After all I got married three times (sequentially, that is).

Trust me Dough no man will hold it against you. The woman mind goes beyond any form of science and logic, and still they are such beautifull creatures.

For though all creatures under heaven are the products of Being,

Being itself is the product of Not-being.

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  • 3 months later...

It is a very slow quenchant. The cold temperature won't do a thing. When you immerse the hot blade, you get a very stable insulating vapor blanket and lots of nitrogen as fog. Now, if it were strogly agitated, you would get a much stronger quench - but you would still have a stable insluating blanket. You would need to agitate it at least 1m/s to do any good - and may require more agitation.

D. Scott MacKenzie, PhD

Heat Treating (Aluminum and Steel)

Quenching (Water, Polymer, Oil, Salt and Mar-Tempering)

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