What would happen (cold liquid)?

[HDB]

What would happen if one would quench in a very cold liquid? Let's say liquid nitrogen. Would it crack into a million pieces, explode,...?

[Stefflus]

Heat of vaporization
Water - 2260 kJ/kg
Ammonia - 1371 kJ/kg
Nitrogen - 199 kJ/kg

Heat capacity
Water - 4.18 kJ/kg·K
Ammonia - 4.7 kJ/kg·K
Nitrogen - 2.13 kJ/kg·K

Heat conductivity
Water - 0.58 W/m·K
Ammonia - 0.540 W/m·K
Nitrogen - 0.065 W/m·K
(Silver - about 410 W/m·K)

So, what steel and from what temperature?
"Cryogenical" quenching of some high alloy steels is quite common, but it's not done with just one quenchant in one go.

What I'm trying to say here is that liquid Nitrogen is a rather poor quenchant, and if you stick a piece of red hot steel into it you might make a woosh of very expensive air. Depending on the steel type and cross section there may be cracking.

silly but enlightening video of "red hot nickle ball into liquid nitrogen"

Edited March 23, 2015 by Stefflus

[Frosty]

As I recall cryogenic treatment of steel is done cold. The action of chilling to those temps (I can't recall the F temp so you guys can look it up if it matters) shrinks the crystaline structure to the point it's crushed to a nearly mono molecular structure, almost amorphous.

We all know (or should know) what a cold shut is and how it works to cause a failure initiation point but I'll summarize just because. Force is conducted through matter in a generally uniform way until it encounters an interruption. When an interruption is encountered the force is stopped, then is conducted across the interruption to continue. Think of this action like pushing two rocks together. You can put a LOT of force on a rock and not mark it but push two together with the same force and both rocks will exhibit crushing at the contact points.

A cold shut is simply a sharp little ding, be it a sharp 90* shoulder or a bit of grit inclusion in a weld, this is an interruption in the uniform conduction of force and ALL the energy is concentrated on each side of the interruption and if the material or structural strength is exceeded THIS is where it WILL start breaking after initiation the material will fail entirely.

You can find the initiation point visually if you look at the break's surface. You will see what looks like a chevron pattern, they are arrowheads pointing directly at the initiation point.

Okay, back to cryogenic heat treatment, super chilling the alloy crushes the crystal boundaries removing the initiation points of uniform force conductivity. Cryogenic treatment has no effect on normal heat treatment and tempering, it basically makes certain alloys much tougher and actually harder but not in the carbon/iron molecule sense.

Anyway cryogenic quench isn't done from critical temperature for all the reasons Stefflus stated. Even liquid helium doesn't have the specific heat nor temperature conduction to do the job on anything thicker than maybe watch springs.

Frosty The Lucky.

[Charles R. Stevens]

It may be a poor quenchant but at the temp's it liquifies at high carbon steel is goin to shatter and the nitrogen is going to splatter. Quench steel in a standarf quenchent, then quench it in the real cold stuff. Even if its just alcohol and dry ice.   

[HDB]

My question was about quenching from the austenitic temperature (hot quenching), not cold quenching (cryogenic treatment, a concept I'm familiar with). I was just wondering what the temperature shock would do to the steel and N₂. Not that it would have any practical use... :-)

[EricJergensen]

You'd either get an eruption of N₂ in your face or a vapor blanket that kept the quenching from happening or both.

Actually, look at the numbers: heat of vaporization of water is 2257 kJ/kg/deg C, for nitrogen it's a piddly 199! You probably couldn't get appreciable hardening with nitrogen at all and next to to thermal stress. That dewar of liquid nitrogen is already at boiling, whereas your water will absorb heat then vaporize and has more than double the specific heat. Even if it were colder than boiling, its thermal conductivity is in the range considered insulator.

In other words, it's not about temperature (of the quenchant). It's about heat. Water will take away heat much more effectively than nitrogen.

[Stefflus]

But ok, with some of the more common refrigerating liquid gasses you might get some spectacular cracking, but also a poisonous or explosive or environmentally hazardous cloud.
I'm guessing the cracking spectacle would be not so different than one brought about by quenching an air hardening steel in water.

[Bo T]

I've worked with LN in the past and sometimes dribbled a little on my hand or arm. There is a sting from the expanding nitrogen gas but no damage. I think a large bubble would form around the hot steel causing a lot of the LN to blow out of the dewar. This could cause injury to the person quenching the blade. It would take a while and a lot of LN to get the blade down to cryogenic temperatures. Because of uneven cooling the blade would probably warp on its way to hardening and it might crack. My guess is from uneven cooling. I'd guess again that the blade would cool more rapidly in oil or water. One danger from LN vaporizing is due to suffocation from displaced oxygen so a well ventilated area is important. 

[ThomasPowers]

Yes what you would get is an "air quench"  As a "science trick" I have stuck my finger in liquid nitrogen---the trick is to move slowly and the liquid never makes contact you just get a N2 bubble around it.  Do not lead with your fingernail as it doesn't transmit heat as fast!!! PLEASE DO NOT BE A STUPID AS I WAS AND REPEAT THIS EXPERIMENT, MISTAKES USUALLY RESULT IN AMPUTATIONS.

Now what you want as a fast quench: look up quenching in mercury.  NOTE VERY TOXIC FUMES GIVEN OFF (If you kill yourself---can I have your anvils and powerhammers?)

(yes much speculation has been made on how I survived to have grandchildren---all I can say is "Live dangerously in as safe a manner as possible!")