Benefit of cryo for D2

J

Jason Fry

Joined
Jun 5, 2008
Messages
3,181
Simple question. Are there benefits to liquid nitrogen cryo for D2? What are they, and is it worth it?
 
I think liquid nitrogen is just used because it is very cheap, I don't think it has any advantages over dry ice because Mf is not that low for any steel. Dry ice may not get as cold, and be more expensive, but it is more readily available and should give you complete martensitic conversion.
 
I just found this following info in this document

Table 1. Rw = FV/WHv, Where F is the normal force in Newtons for pressing the
surfaces together, V is the sliding velocity in mm/s, W is the wear resistance in mm/s, and
Hv is the Vickers hardness in MPa. Rw is a numeric value
Wear Resistance, Rw(n)

Alloy Untreated Soaked –196 ◦C( –310 °F )

52100 25.2 115
D-2 224 878
A-2 85.6 565
M-2 1961 3993
O-1 237 996
Click to expand...

I don't think I have heard of cryo treating of O-1 before but according to this, the wear resistance is better than D-2...!!! Could it really be?

Also a couple more publications I came across:

Cryogenic treatment of tool steels

Thesis work of a japanese student
 
liquid nitrogen is used primarally because it is easier to store (in a proper tank several months) and since it ids a liquid I can imagine that procces working better
 
69_knives said:
I just found this following info in this document

Table 1. Rw = FV/WHv, Where F is the normal force in Newtons for pressing the
surfaces together, V is the sliding velocity in mm/s, W is the wear resistance in mm/s, and
Hv is the Vickers hardness in MPa. Rw is a numeric value
Wear Resistance, Rw(n)



I don't think I have heard of cryo treating of O-1 before but according to this, the wear resistance is better than D-2...!!! Could it really be?

Also a couple more publications I came across:

Cryogenic treatment of tool steels

Thesis work of a japanese student
Click to expand...

Very interesting! I never knew about the martensitic conditioning aspect, but it suggests that liquid nitrogen is not cold enough. Liquid helium would be needed for cryo. An alternative would be to leave the knife in outer space for a month.
 
Last edited:
mete said:
That Irish paper is nicely written - no dumb hype .
Click to expand...

If deep cryo removes the secondary hardening response, would you still temper steels like M2/M4 the same way, or use the low temper instead?
 
The article points out that each steel is different and must be treated so. In addition HT is different depending on what you want as far as properties. The article doesn't have graphs for toughness unfortunately. We normally ,for blades , look at hardness, toughness and wear resistance and pick a good compromise . If the cryo removes secondary hardness in M4 then we have to look at toughness to decide on tempering temperature.
 
Ive experimented and researched cryo.

1. The deep cryo -300F is better than "normal" cryo. Theres papers on it that show this.

2. The benefits I found with further reducing retained austenite can also be achieved through other means such as multiple heat treating cycles.

3. Knife tribology is not properly understood in scientific terms so I would take claims about wear resistance with some scepticism. There is allot to tribology and there is numerous different ways parts can wear.

4. I have observed better wear resistance using cryo but I later discovered that refining the grain size through multiple heat treat cycles gave the same effect. It also improves toughness.

Mete makes a good point about toughness and I'd be interested in any papers that explore toughness with cryo. My blades are specifically designed for toughness, strength and hardness.
 
nullack, you need to try liquid helium, and tell us how the knife performs. Not sure where to obtain it, but people have use liquid helium to overclock their computer for video games. I will ask my local university, CalTech, if they have some.
 
nullack said:
Ive experimented and researched cryo.

1. The deep cryo -300F is better than "normal" cryo. Theres papers on it that show this.

2. The benefits I found with further reducing retained austenite can also be achieved through other means such as multiple heat treating cycles.

3. Knife tribology is not properly understood in scientific terms so I would take claims about wear resistance with some scepticism. There is allot to tribology and there is numerous different ways parts can wear.

4. I have observed better wear resistance using cryo but I later discovered that refining the grain size through multiple heat treat cycles gave the same effect. It also improves toughness.

Mete makes a good point about toughness and I'd be interested in any papers that explore toughness with cryo. My blades are specifically designed for toughness, strength and hardness.
Click to expand...

Multiple full heat treat cycles or multiple tempering cycles?
 
JBS thats a question I have not fully answered yet. I have been doing triple normalising, single quench and triple tempering. Others such as Ed Fowler does triple quenching as well. Im yet to have a clear scientific observation on any differences.
 
cotdt said:
nullack, you need to try liquid helium, and tell us how the knife performs. Not sure where to obtain it, but people have use liquid helium to overclock their computer for video games. I will ask my local university, CalTech, if they have some.
Click to expand...

Mate what would that do? The deep cryo I had done is computer controlled and certified to many standards by a professional heat treat shop.
 
nullack said:
Mate what would that do? The deep cryo I had done is computer controlled and certified to many standards by a professional heat treat shop.
Click to expand...

Liquid helium allows you to acheive -450F which is a lot colder than liquid nitrogen. The paper strongly suggests that there would be a benefit in refining the carbide structure of the steel.


How about this heat treat for D2:
Preheat 1200F 30 minutes
Preheat 1450F 30 minutes
Austenize 1875F 30 minutes
Air/plate quench to room temperature
Cryo in liquid helium 1 day
Temper 500F 2 hours

Should end up with 61-62 hrc with the cryo.
 
Last edited:
The carbide formation in tempering that gets set up by the cryo treatment would probably slow down in liquid helium, so you might have to go a lot longer than 24 hours.
 
Achieving (mostly) full martensite conversion is the primary purpose of "cryo"



nullack said:
Ive experimented and researched cryo.

1. The deep cryo -300F is better than "normal" cryo. Theres papers on it that show this.

2. The benefits I found with further reducing retained austenite can also be achieved through other means such as multiple heat treating cycles.

3. Knife tribology is not properly understood in scientific terms so I would take claims about wear resistance with some scepticism. There is allot to tribology and there is numerous different ways parts can wear.

4. I have observed better wear resistance using cryo but I later discovered that refining the grain size through multiple heat treat cycles gave the same effect. It also improves toughness.

Mete makes a good point about toughness and I'd be interested in any papers that explore toughness with cryo. My blades are specifically designed for toughness, strength and hardness.
Click to expand...



Multiple heat treating cycles may work marvelously for something like 52100, but it won't work well for D2 and high speed steels, and most likely won't work for 3V and many tool steels. The reason is the carbide condition before austenitization dictates grain size. So D2, on the first HT would have a grain size of 10 (moderately fine). Upon the second HT the grain size grows to size 3 (very large). It would have to be re annealed and re spheroidized. The same is true for HSS and many others. And multiple tempering doesn't do it either. The best way to to reduce RA in D2 (which is designed to retain it) is trip to Mf as part of the quench. Mf for D2 can vary but is frequently around -100 F.

I have seen many "papers" that have "shown" vastly different amounts of wear resistance in steels subjected to different levels of cryo. Different times and different temps etc. There was an impressive amount of difference "shown" there. But in my real world experiments I have seen very little real difference. -100 for a hour works as well as -300 for a day, in D2. And I attribute this to RA conversion. Now, for sure, the difference between cryo and nothing is huge in a steel designed to retain austenite.
 
Thanks for that Nathan. I wasnt aware that only some tool steels could get grain refinement through multiple heat treating cycles. Do you have some sources of info so I can learn more about this?
 
Table 1. Rw = FV/WHv, Where F is the normal force in Newtons for pressing the
surfaces together, V is the sliding velocity in mm/s, W is the wear resistance in mm/s, and
Hv is the Vickers hardness in MPa. Rw is a numeric value
Wear Resistance, Rw(n)
Alloy Untreated Soaked –196 ◦C( –310 °F )
52100 25.2 115
D-2 224 878
A-2 85.6 565
M-2 1961 3993
O-1 237 996
Click to expand...

help me with this chart it cant possibly mean that cryo 52100 is 4.6 x more wear resistant than regular
or that cryo m2 is 15.8 x more wear resistant then regular 52100?!?!:eek:

try this its really long and takes sume sifting through, but there is good information
http://books.google.com/books?id=cYzNYwMtQHcC&pg=PA238&lpg=PA238&dq=cryo+heat+treating+M4&source=bl&ots=6z3P8nWfrY&sig=XRBDjd-c0-x9aU2NvNrlAf6oVec&hl=en&ei=3szDSt-GIsXM8Qb-hu3fCQ&sa=X&oi=book_result&ct=result&resnum=1#v=onepage&q=&f=false
 
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