Liquid Nitrogen vs Dry Ice

If you see gains in HRC in low alloy steels like 52100 from a freezer treatment, (or sub zero or cryo) there was too much retained austenite in the steel after your hardening procedure. 1475f seems to be the sweet spot for hardening low alloy hyper-eutectoid steels, as it puts just enough carbon in solution for max HRC (66-67+), but not so much that you get excessive retained austenite. It is the conversion of that RA into untempered martensite by subzer/cryo that shows a gain in HRC. Lower than 1475f, not enough carbon in solution, lower than expected HRC. Higher than 1475f, too much retained austenite present, lower than expected HRC, and the freezer/sub zero/cryo would bring the HRC back up where you want it to be.

That is my understanding.
 
Tai goo, fowler and Cashen in the same thread..I fondly remember those days.:D.
I really,really wish Kevin Cashen was still around..He had a knack for such great solid info and sharing HT recipes with other knife makers..Many of his heat treats are still the standard for a lot of smiths..
 
Stuart is right, but I quit beating that horse a long time ago.
Despite what some cowboys tell you in the magazines. Sticking 52100 or 5160 in a home freezer overnight won't gain anything perceptable... unless you didn't do the HT right in the first place.

Even if there is a theoretical gain, the large gains stated by some of those folks is greatly exaggerated. Most people don't have testing equipment sensitive enough to tell if there was a gain or not. I bet the average person couldn't test two identical knives and tell which was quenched, cooled to room temp, and then tempered - and which was quenched, cooled to -100F, and tempered. Certainly no one could tell between room temp and a 10F freezer.
 
Yea, Ill try not to get too much into it because its a coal mine sized rabbit hole..Anyway we use Kevins heat treat for 52100..We do have a few real old school makers here about that use the freezer method with about a 366° temper for 60rc.. About a year ago one of them would not hush about his 52100 getting as hard as possible,home freezer this and that until I asked "if your 52100 is getting max hardness out of the quench then how come your only at 60rc with a 366° temper.. if I tempered mine at 366° it'd likely still be 64rc anyway because it hits 66-67 out of the quench.. Though hes also one that said align your quench tub true north to avoid warps so theres that too
 
I found that after all the drama of "putting in a freezer does nothing" that Larrin shows that for some steels it is better then letting it set at room temperature.

Very interesting.

I am just happy I have access to real liquid nitrogen cryo when needed
 
I was able to find some reliable retained austenite numbers on 52100, included in Appendix A, page 9b: https://dspace.mit.edu/bitstream/handle/1721.1/70610/07354787-MIT.pdf?sequence=2

Each was austenitized for 25 min. 1500°F - 8%, 1550°F - 15%, 1600°F - 18%. So the presence of retained austenite is confirmed, and this is not a surprise except to those who still want to hold to the idea that low alloy steels won't have retained austenite. Using a tempering temperature of 450°F led to the elimination of retained austenite but unfortunately this also correlated with reduced toughness due to tempered martensite embrittlement. Lower tempering temperatures did not eliminate retained austenite.
 
So.... Austenitizing 52100 at 1500F and using a cold treatment for RA prior to temper would both eliminate the RA more completely AND result in greater toughness? Or does the martensite embrittlement not occur with the lower tempering temperature required for RA conversion after cold treatment?

ETA: Everything in life seems to be a 3 legged stool.
 
kuraki said:
So.... Austenitizing 52100 at 1500F and using a cold treatment for RA prior to temper would both eliminate the RA more completely AND result in greater toughness? Or does the martensite embrittlement not occur with the lower tempering temperature required for RA conversion after cold treatment?

ETA: Everything in life seems to be a 3 legged stool.
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The study showed that lower austenitizing temperatures led to superior toughness even when at the same hardness, down to 1500°F anyway. Using a cold treatment wouldn't necessarily increase toughness as retained austenite can improve toughness. Lower tempering temperatures would not lead to tempered martensite embrittlement.
 
Sorry, I didn't mean that the cold treatment would increase toughness, but that by utilizing a cold treatment and lower tempering temp, you could achieve same or better reduction in RA without the martensite embrittlement caused by the 450F tempering temp.

So effectively utilizing cold treatment increased HRC (because lower tempering temp used) reduced RA (via cold treatment and conversion in temper) and increased toughness (lower tempering temp, no embrittlement).

Or maybe I misunderstood.
 
kuraki said:
Sorry, I didn't mean that the cold treatment would increase toughness, but that by utilizing a cold treatment and lower tempering temp, you could achieve same or better reduction in RA without the martensite embrittlement caused by the 450F tempering temp.

So effectively utilizing cold treatment increased HRC (because lower tempering temp used) reduced RA (via cold treatment and conversion in temper) and increased toughness (lower tempering temp, no embrittlement).

Or maybe I misunderstood.
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Got it now. That's why I was restating things because I wasn't sure I was following you.
 
I wish you all would get over the RA paranoia . In all my days with tool steel we knew that you'll get some RA and it often was useful for toughness . Pick a steel and look at ALL the variables to get the best mix for the application !
 
mete said:
I wish you all would get over the RA paranoia . In all my days with tool steel we knew that you'll get some RA and it often was useful for toughness . Pick a steel and look at ALL the variables to get the best mix for the application !
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I'm not sure one thread means paranoia.
 
Larrin , I've been on this forum many years and I know it's not one but many threads and posts over the years . Stick around and you'll see ! :eek::rolleyes:
 
mete said:
I wish you all would get over the RA paranoia . In all my days with tool steel we knew that you'll get some RA and it often was useful for toughness . Pick a steel and look at ALL the variables to get the best mix for the application !
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Is discussing what is happening really paranoia or just education?
 
mete said:
Larrin , I've been on this forum many years and I know it's not one but many threads and posts over the years . Stick around and you'll see ! :eek::rolleyes:
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mete's Bladeforums join date: June 10, 2003
Larrin's Bladeforums join date: January 17, 2004

I think we can describe the mechanisms of retained austenite transformation without obsessing about one part of heat treatment. We have to take things one at a time.
 
“Tool Steels” 4th edition page 346 has a little info on 52100 regarding quench speed and retained austenite.

Quenched from 1550*; water quench = 5.8% ra, oil quench = 7% ra, salt-quench to 450* then water quench = 6.1% ra, salt quench to 450* then oil quench = 6.2% ra, salt quench to 450* then air cool = 10.6% ra.

I would think you could get very low or no ra with a sub-zero or cryo quench, if that’s what you want.

Hoss
 
The reason for my question was less about 52100 and more about how I think a lot of tribal knowledge (in any industry) is accumulated by situations like this. Where you have intertwined variables and one or more isn't exactly observable, but is affected by changes in the others. And in knifemaking in particular since it's largely an individual pursuit.

So something like cold treatment effectively increasing toughness or RC where one wouldn't normally expect it (within a set of conditions), is observed, the correlation is assumed to be causation and becomes "fact" in the observers perspective, and even if the effect is understood or explainable, it's hard to get people who have accepted that "cold treatment does x" to understand why it did in this case and how that may not be the ideal way to accomplish a particular end goal. Because it's doing something remedial and in ideal conditions would be less helpful (or not at all).

It's like milling a guard slot. What is the best practice? Guy A has figured out that he can can mill a guard slot to a press fit, but because he doesn't have a surface grinder and his tangs are not flat and parallel, he ends up peening guards to get a tight fit. He concludes it's impossible to mill a guard to a tight fit without some hand fitting/peening. Guy B surface grinds his tangs and mills them to .001 interference and has no problem getting a tight fit. And they get into a discussion that revolves completely around milling and peening while ignoring the flatness and paralellism of the tang variable.
 
AVigil said:
Larrin Larrin so would putting a 52100 blade in the freezer have any gains in Rockwell hardness as explained by Fowler?
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Adam the problem with Ed's claims of various types, including freezer'ing, multi quenching, etc, wasn't that the things he did or claimed, couldn't lead to improvements or have effects, it was that he made wild assertions about what types of improvements, which constantly varied and were often vague (and/or he simply didn't understand, but saw/felt improvements and jumped to conclusions), and treated it all like religious voodoo, that if anybody questioned, was a blasphemer.

Such to the point that the knee jerk, and understandable reactions by those that understood the science more than him, led many others to come to the opposite conclusions, such that there are plenty of people now convinced, for instance, that quenching more than once does absolutely nothing under any circumstances, etc. because one very vocal character portrayed it very differently than reality.

It's the same thing with differential hardening, the edge quenchers ruined it, because people assume that differential hardening means the same thing. The "edge packers" discredited the effects of forging (which can be good, or bad, depending on circumstances), and the list goes on and on due to hyperbole and general lack of many to be cautiously optimistic with a real desire to understand what's happening, good or bad, ultimately, due to deep seated personal insecurities. ;)
 
kuraki said:
The reason for my question was less about 52100 and more about how I think a lot of tribal knowledge (in any industry) is accumulated by situations like this. Where you have intertwined variables and one or more isn't exactly observable, but is affected by changes in the others. And in knifemaking in particular since it's largely an individual pursuit.

So something like cold treatment effectively increasing toughness or RC where one wouldn't normally expect it (within a set of conditions), is observed, the correlation is assumed to be causation and becomes "fact" in the observers perspective, and even if the effect is understood or explainable, it's hard to get people who have accepted that "cold treatment does x" to understand why it did in this case and how that may not be the ideal way to accomplish a particular end goal. Because it's doing something remedial and in ideal conditions would be less helpful (or not at all).

It's like milling a guard slot. What is the best practice? Guy A has figured out that he can can mill a guard slot to a press fit, but because he doesn't have a surface grinder and his tangs are not flat and parallel, he ends up peening guards to get a tight fit. He concludes it's impossible to mill a guard to a tight fit without some hand fitting/peening. Guy B surface grinds his tangs and mills them to .001 interference and has no problem getting a tight fit. And they get into a discussion that revolves completely around milling and peening while ignoring the flatness and paralellism of the tang variable.
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True words, although this is a symptom of our greater culture. Hell I've got a running joke with my maker buddies that I hang with locally about "That's not how Nick Wheeler does it", everytime one of us shows, or comes up with a new way of skinning some cat, because we've literally heard this from "know it all internet geniuses" in ABS classes, taught by Mastersmiths, where some nimrod will argue with the teacher's technique because of some video of Nick's. It's not Nick's fault, he's a great maker, sharing a lot of good information, about *his* methods, however, because he's been so active on social media/forums and especially making instructional videos, there are beginners that pretty much view his information as gospel, even though they don't understand it.

Honestly it's understandable, we all want things to be simple and "finite", and there's been a pretty strange cultural shift regarding "science" to be revered as "objective" and definite, I suppose, to take place of religion in an exceedingly secular culture. I guess people need something to have "faith" in, regardless, otherwise they'd be living in constant fear of the unknown (as if they weren't already lol).



Haha, how's that for a digression?


Either way, entertaining thread guys, I'm not hot enough on the deep metallurgical side to contribute directly, but I've been watching these threads with great interest to learn more.
 
I'm still curious of what impact maximizing carbon in solution at austenitization has on performance for low alloyed steels, assuming that the increased RA will be removed with cryo thereafter. Seems like it would be an interesting experiment with a couple of simple steels like 1095, 52100, O1, W2, etc. Maybe 3 samples of each steel with progressively higher austenitizing temperatures for each different sample to maximize carbon in solution, then all get cryo, and finally hardness testing and charpy testing to determine the effects. I realize there is a grain size component as well as free carbon component so it would not be entirely easy to tease out results, but it would still be interesting to see.
 
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