Sub-Zero Quench hardness gained vs Cryo?

Wolf Creek Forge

Wolf Creek Forge

Joined
Jul 4, 2012
Messages
533
Ive been reading a lot about sub zero and cryo treatment.Now I know the whole point is to reduce RA but Im curious.Most of what I have read here and other places people are saying that they gain no hardness with cryo over subzero quench..Seveal posts Ive read say they get the same RC readings after both..Now Im not trying to go into the whole nano carbide formation argument( but if you want go ahead and knock yourself out,LOL) . Im really wanting to know if you have ever seen a significant hardness gain in cryo over sub zero quench or are we just talking nano carbide formation?
 
Last edited:
I'm not at all convinced by reports of massive gains in hardness and/or wear-resistance from LN cryo (some folks have claimed 500% increase... that just doesn't add up).

I am however, convinced of significant improvements in fine-edge stability and toughness... both of which I believe are due to high-alloy steels being fully quenched, and the more complete transformation of austenite into martensite (which must still be tempered). I can't speak to the nano-carbide thing at all.

Rockwell readings by themselves can be deeply misleading, anyway... we can temper 1095 and CPM-3V to the same 58Rc reading and they will have vastly different characteristics in every factor we measure blades by. (wear-resistance, toughness, sharpenability, corrosion-resistance, etc.)

It's a huge and fascinating topic, and it depends a great deal on the alloy being used, and whether we're talking about -80F or -300F, and austenizing temps, soak times, and before-or-after tempering...
 
Last edited:
Well Im speaking more per say A2 or 154cm, same heat treat but using sub zero quench instead of full cryo..Just for instance..
 
I suspect that the more alloying elements involved, the more important it is to employ deep cryo to complete the quench. Many alloys may get 75% of their potential from air- or plate-quenching alone, 90% of their full potential from a dry-ice quench, and the extra bit they gain from LN may either not exist, or be so small that we couldn't tell anyway.

Simpler alloys like 10xx, O1 and so on probably don't need a cold treatment at all.
 
I have never used dry ice sub zero quench but I do use LN cryo.I know I get 1-1.5 point higher Rc numbers with cryo than without.Also as James said better fine edge stability and toughness. I use CPM 154 for 90% of my knives.

Stan
 
Now the real answer since you must have forgotten any of my previous comments ! LOL.
Sub-zero at -100 F reduces retained austenite.
Cryo at -300 F reduces retained austenite and permits the formation of the small 'eta' carbides which may increase hardness as much as 2 points HRc. A bunch of variables here. Alloy ,HT etc. Eta carbides make the difference !
 
Unless you have a way to test Rc anyone can say whatever they want. I've air hardened steel,
plate quenched, frozen plate quenched, dry ice and alcohol, and LN. While doing this making it as much of the quench as possible, in other words no big interruptions. My take is this most people that argue about
any or all of the above either don't have a way to test steel, don't have a way to do it, or simply do not want
to take the time. I'm with Stan and Mete on this I do believe and will continue to treat, quench, freeze and
draw blades to the best of my ability.
Ken.
 
I agree with James Terrio. On simple carbon steels, a sub-zero quench has no effect (other than making the metal cold). You should see some results with A2 and 154CM. I've noticed that the greater the alloying elements (such as with air-hardening steels), the greater the effect. 1-2 points extra Rc and noticeable wear resistance.
The sub-zero treatment needs to follow the hardening procedure fairly soon. After about ten days, any retained austenite reverts back to pearlite. Keep in mind that sub-zero quenching produces fresh martensite, so another tempering procedure is necessary.
As I understand your question, you are wondering about comparative differences between dry ice (-100F) and liquid nitrogen (-300F). I'm sorry that I did not answer your question. I would, however, be interested in your results if you choose to try some tests. I have only used dry ice and I have noticed a difference even with L6.
 
mete said:
Cryo at -300 F reduces retained austenite and permits the formation of the small 'eta' carbides which may increase hardness as much as 2 points HRc. A bunch of variables here. Alloy ,HT etc. Eta carbides make the difference !
Click to expand...

Dead serious here, I am sincerely interested to see any documentation about formation of small "eta carbides" in high-alloy steels. I've heard quite a bit about the theory, but I'm having a really hard time finding any proof. My HT guy, and the guys I buy my steel from, tell me it's a wild goose-chase and I shouldn't even concern myself with it.
 
I know very well that hardness isn't everything and that it depends on the steel at hand. Though for this question I'm talking about the same steel heat treated the same way.Will the steel coming out of the cryo be harder than the steel using a subzero quech instead? The reason I'm wondering is that I've read that it won't by people who say they have tested the hardness side by side. Now the reasom I'm asking here is that we know many of you guys and trust your opinions more than opinions of random armchair heat treaters. Eventually I will test for myself but right now we don't have LN. So right now it's a curiosity question.
 
It seems that every steel will behave differently. I have a paper in front of me that compares several heat treatment procedures for an M2 steel, C-1.269, Cr-4.288, Mo-3.005, W-5.88, V-4.56, Fe-77.67 by OES. The increase in hardness, over conventional (air cooled to room), for dry ice and LN and a single 600 C temper was @ 61.5 - 62.5 - 63.0 HRc. But, the increase in hardness was usually accompanied by a decrease in toughness. i.e. conventional single temper gave an impact energy of 3.6J at @ 61.5 HRc. Dry ice with 2 600 C tempers gave HRc @ 61.7 with an impact energy of 3.5J. Triple tempered LN gave an HRc @ 62.3 with an impact energy of 3.3J.

Influence of deep cryogenic treatment on alloy carbide precipitations and mechanical properties of AISI M2 high speed tool steel, A Bensely et al.
 
It took me years to find such info !!! I don't now how to easily send what's on my computer to the forum .It's on Springer but I'll write it out.

IntJ Adv Manuf Technol
DOI 10.1007/s00170-010-2935-5
Metallurgical Principles of Cryogenically Treated Tool Steels
Gill, Singh, Singh, Singh 2010

Yes each steel is different !!
 
I am lucky, I stumbled upon a source after a few months. Although many are just abstracts.

http://www.cryogenictreatmentdatabase.org/

The time and effort to examine a single steel across a few parameters in the paper I cited included 7 researchers across 7 institutions and 3 countries.
 
You must log in or register to reply here.
Back
Top