Cryo?

me2

Well-Known Member
#41
Something I have been wondering about is the ETA carbides that form in cryo, but not sub-zero. IIRC, they are only there after cryo, and once tempered they dissolve. Is this true? At a structural level, what improvement would cryo result in over sib-zero, as long as Mf is reached by -110f? It seems obvious that Mf at -200f would benefit from cryo, but that's not what we are talking about here.
The stuff I read indicated the eta carbides did not form directly from the cryo treatment, but the ultra cold temperatures conditioned the martensite and led indirectly to the formation of eta carbides during tempering.
 

Doug Lester

Well-Known Member
#42
Warren, I'll have to agree with you in the broadest sense but I used to me a med tech before I retired and I've seen some scientifically developed tests that weren't worth crap. The studies were cooked before being submitted to the FDA for approval. Scientists and those who attempt scientific studies are supposed to approach testing without any predetermined outcome in mind but we're all fallible human beings.

Doug
 

scott.livesey

Dealer - Purveyor
#43
Do you have any examples of the changes that could be made and then buried to make hardness go down after cold/cryo treatment? Is anyone actually claiming the hardness goes down after cold/cryo? If so, did they give an explanation or mechanism as to why?
here is the article i referenced. http://www.industrialheating.com/ar...ogenic-treatment-on-properties-of-tool-steels
"The hardness of CT samples (-196˚C/-230.8˚F for 4 and 10 hours) is about 2.5 HRC lower than that of VANADIS 6 with no CT and is the same as after deep cooling to -90˚C (-130˚F) regardless of the subzero holding time."
"Generally, there are no significant advantages that would prolong the lifetime of tools by providing higher wear resistance and toughness. We can perceive certain improvements, but CT does not make sense considering the economics. Real experiments with tools made from VANADIS 6 did not show a longer life cycle."

this is an article written by folks that own and operate a heat treat facility in the Czech Republic.
my point is that cryo has been around a long time and what it can do and can't do is still open for discussion.
 
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#45
Warren, I'll have to agree with you in the broadest sense but I used to me a med tech before I retired and I've seen some scientifically developed tests that weren't worth crap. The studies were cooked before being submitted to the FDA for approval. Scientists and those who attempt scientific studies are supposed to approach testing without any predetermined outcome in mind but we're all fallible human beings.

Doug

Now that's the way I was always told it was supposed to be and I tend to agree with that point of view. :)

I believe in straight forward 100% honesty, anything less isn't tolerable.
 
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me2

Well-Known Member
#46
here is the article i referenced. http://www.industrialheating.com/ar...ogenic-treatment-on-properties-of-tool-steels
"The hardness of CT samples (-196˚C/-230.8˚F for 4 and 10 hours) is about 2.5 HRC lower than that of VANADIS 6 with no CT and is the same as after deep cooling to -90˚C (-130˚F) regardless of the subzero holding time."
"Generally, there are no significant advantages that would prolong the lifetime of tools by providing higher wear resistance and toughness. We can perceive certain improvements, but CT does not make sense considering the economics. Real experiments with tools made from VANADIS 6 did not show a longer life cycle."

this is an article written by folks that own and operate a heat treat facility in the Czech Republic.
my point is that cryo has been around a long time and what it can do and can't do is still open for discussion.
Thats some pretty good information. It appears the secondary hardening in the non-CT pieces made out paces the as quenched hardness gains whwn tempering at the same temperature. Were it heat treated as bossdog did, with cryo and a low temper, the cryo'd samples likely would have been ahead.
 
#47
Hmmm...interesting reading. I, for one, don't want to sign up to a website to read non-scientific data, however. I'm assuming Me2 did read it and found out that tempering temps were not adjusted to optimal with cryo treatment??? What other variables were either not considered or ignored?

Show me double-blind studies comparing "optimal" HT proceedures with and without cryo for each alloy and I will START to question the many years of contradictory evidence. I would say..."Just goes to prove that most pre-conceived theories can be "proven" by non-scientific studies". But...that would be rather hypocritical of me to accept such "proof" considering I postulate the same and no one has done a double-blind study to prove that non-scientific studies can actually prove most pre-conceived theories :what!::biggrin:
 

me2

Well-Known Member
#48
Hmmm...interesting reading. I, for one, don't want to sign up to a website to read non-scientific data, however. I'm assuming Me2 did read it and found out that tempering temps were not adjusted to optimal with cryo treatment??? What other variables were either not considered or ignored?

Show me double-blind studies comparing "optimal" HT proceedures with and without cryo for each alloy and I will START to question the many years of contradictory evidence. I would say..."Just goes to prove that most pre-conceived theories can be "proven" by non-scientific studies". But...that would be rather hypocritical of me to accept such "proof" considering I postulate the same and no one has done a double-blind study to prove that non-scientific studies can actually prove most pre-conceived theories :what!::biggrin:
I'd have to reread it at this point, but I don't think they were ignored. It might be that they need some temperature resistance for their intended purpose and thus the low tempering range is not an option. In any case, cryogenic treatment and results are highly specific to steel and application. It doesn't always help for every steel, as was once thought.
 
#49
This is one of those threads that I usually try to steer away from-just not often enough. Remember that the thread started was dealing with D2, stainless steel, and other complex alloys and not something as relatively simple as even 52100. With some alloys, as indicated by their data sheets, cryo or even just cold treatment does make an improvement. Other steels you're just making cold. The formation of eta-carbides and their significance seems to be a area that is still under research and discussion.

As far as people putting their garbage out there, remember it goes both ways. I get frustrated at people who don't have the ability to isolate and test the variables involved reject decades of metallurgical science for their own pet theories and they get tired of me quoting Verhoeven and other authors of books on metallurgy. We just need to try real hard and treat each other with respect and know when to back off. Remember, never argue with an idiot. They'll drag you down to their level and beat you with experience.

Doug
Doug I'm with you, I think you are clearly seeing the forest for the trees.
 
#50
Something that has not been discussed yet is the fact* that one can heat the (high carbon) steel to a higher temperature when "cold treating" it (be that in a deep freezer, with dry ice, or with liquid nitrogen...) than without the cold treatment (as the cold treatment reduces the excess RA produced by the higher HT temperature), and that will normally result in an increased hardness with high alloy steels.

Of course, it is not necessary better to have that increased hardness - that would depend on blade geometry and intended use...

* as per Sandvik's recommendations for 12C27: HT to 1080 °C and tempered at 175°C without cold treatment (i.e. only cooled to 20°C) should result in 59 HRC, whilst HT's at 1090°C with cold treatment to -70°C should result in 61 HRC
 

Doug Lester

Well-Known Member
#51
Yes, you can correct for elevated retained austinite that was created by poor heat control in heat treating high carbon steels. I would question being able to do so in the kitchen freezer. Dry ice and acetone might get you there. Refer to the data sheet for the steel. Liquid nitrogen should get the job done. Of course one could avoid the problem with proper heat control and not form the retained austinite in the first place or restrict yourself to steels of 85 points carbon or less that don't have the problem with becoming super saturated with carbon and triggering the formation of significant amounts of RA. Also when you get down into this range of carbon into solution, either by choice of steels or restricting the amount of carbon put into solution, tempering will allow carbon to escape the iron matrix and the conversion of retained austinite to untempered martensite.

Doug
 

samuraistuart

Well-Known Member
#52
(I just saw Doug posted at the same time!)

Alloy steels like stainless do benefit from sub zero/cryo treatments because the alloying in them basically requires the sub zero in order to reach full Mf (theoretic). Like the Sandvik series, AEB-L being another good example of how cryo treating or sub zero treating an alloy steel will increase hardness levels.

I don't think the deep freezer offer much to us in the way of sub zero treating steel. If RA is a major concern, then I suppose 0 degrees F is better than room temp, but likely not enough of a change to be noticeable...if at all. I know there are some well known and well respected knife makers who swear by the home deep freezer. I do have my doubts on that....but respect all.

Carbon steel differs from the stainless steels in that it generally does not have enough alloying in it to lower Ms or Mf considerably, nor do we heat treat it in a way to cause a lot of RA. A2 being an exception to that. Hardening at 1750F, I would think sub zero would be a good way to go with A2.

The way I see it (I am always learning from you guys) you have two options in heat treating. Higher hardening temp or lower hardening temp. If you go with the higher temps, yes, the sub zero can be your friend by changing over the RA. If you go with the higher hardening temps, the RC hardness will actually drop. There is a "sweet spot", so to speak, with carbon steel......8% or so. If you only put about .8% carbon in solution (1475F), then you leave the rest of the available carbon as carbide, and you'll have, practically speaking, no RA to deal with.
 

stezann

Well-Known Member
#53
Be aware that 1475 °F is not a "0.8%C temperature" valid for all steels.
In presence of hungry alloy elements :)3:) you have to snatch the carbon from their carbide hands with high temperatures, they won't let go 0.8%C into solution at 1475 °F.
With the prescribed austemps for AEB-L you get just a bit more than 0,6%C into the austenite and 0 °F will get you so close to Mf, the RA is irrelevant.

I must admit i don't believe in liquid nitrogen, and so it appears to me like water quenching (or superquenching!!!) oil hardening steels....if cold/fast will take me home, colder/faster has to be super cool ;)

This rush to the maximum theoretical hardness in my opinion lacks the whole view we ought to have about steel. One single property doesn't make the steel, it is a combination of features that makes steel a nice blade material. A carbide knife blade won't hold the acute angle required for slicing.
A blade full of RA won't hold the same edge too, but the best compromise between hardness and toughness is a valid target worth pursuing.
I won't chase eta carbides inside a Dewar to find brittleness, but i'm sure interested in reading the studies about it and learn something new if something is there.
 
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BossDog

KnifeDogs.com & USAknifemaker.com Owner
#54
I'm not sure that cryo treatment is a remedy for poor heat treating. I see it as an extension of the heat treat/quenching process that helps maximize conversion of RA to martinsite.

While we know a great deal about the heat treating process, we don't know it all and labeling cryo treatment as a fix for a bad process maybe isn't the best way to describe it. Most of us don't have industrial heat treating equipment or the ability to analyze or measure carbide size, grain, etc of the internal structure of steel. We also don't have the equipment to accurately measure toughness, edge retention or corrosion resistance. We have to rely on experience and observation and public data.

I cryo stainless blades every time I make one because my cutting tests done a long time ago proved to me there is improved edge retention in the process. I can't say I understand exactly why, I just know what I observed.

We do have enough empirical data to know that not all steels respond the same to cryo treatment. That doesn't mean the process lacks merit. To my mind, it means we have more to learn.
 
#55
Wise words from the Bossdog here. What almost always gets omitted from online cryo discussions is the simple-simple/complex-complex component, as in the simpler the alloy, the simpler the heat treatment, the more complex the alloy, the more complex the heat treatment. Is cryo effective in improving things like edge stability via retained austenite conversion? Absolutely, but it is not a yes/no thing, it is a gradient thing. For every alloying element added to the steel things like cryo become more relevant in their effectiveness. In a 10XX series steel a smidge of Mn is all you have as far as complications beyond carbon levels, and carbon levels are entirely under your control by your soak practices, so if you are getting any levels of retained austenite that are noticeable it is telling you something about your heat treatment that needs to be addressed so that you don’t have to resort to cryo.

But the O.P. asked about heavily alloyed steels, approaching and including stainless. While you can control how many carbon atoms occupy the interstitial spaces in the iron lattice, and thus reinforcing the austenite, you cannot under-heat or soak away the amount of distortion by the substitutional alloy atoms such as chrome, nickel* etc… So even with the best control over soak temperatures you are going to have austenite that is resistant to conversion. What this does is push the Mf (the point at which you will have converted the maximum austenite which is more often referred to as something like M94% these days) below room temperature on the cooling curve. With steels like this you obviously need something colder than air or room temperature oil to finish the job. In this situation cryo is not propping up or fixing an improper heat treatment, it is the continuation of a proper and thorough heat treatment.


So, starting with the steels the O.P. mentioned, cryo (or cold treatment) is necessary if you want complete austenite conversion, but becomes less necessary with every alloying element taken out of the mix until you reach simple carbon steels where the problem can indeed be handled without freezing by careful and precise soaking and quenching.

*Nickel is so effective in stabilizing austenite that it is the element that is used to make austenitic stainless which is always completely austenitic and non-magnetic, even at room temperature.
 

stezann

Well-Known Member
#56
While sub zero treatments of high alloyed steels are obviously required for the above explained reasons, i am still confused about the tempertaures actually required to complete the transformation.
Is liquid nitrogen necessary to complete the martensite transformation for certain alloy or the temps reached by dry ice could be enough? I'm talking about just Mf, not considering the aspects related to precipitation of eta carbides.
 

Knifemaker.ca

Dealer - Purveyor
#57
There is a process reason to use LN as well. If I buy dry ice, seems like nomatter what I do, It is gone in 24 - 48 hours. If I fill my liquid Nitrogen Dewar, I'm good for 6 weeks of more. Of course, this wouldn't matter to those who only do a few here and there.
 

scott.livesey

Dealer - Purveyor
#58
you need to read the label to see what temperature you need. AEB-L or sanvik 12C,13C steels say -95F (http://www.smt.sandvik.com/en/produ...ife-steel/hardening-guide/hardening-programs/) which is dry ice and acetone or alcohol. more complex stainless needs LN. I have not found any other coolants available. i guess you could use LOX, but that is like juggling bottles of nitroglycerin. back to the original question of this thread, do your own research. if your computer is capable of getting you to this forum, it is capable of researching cryogenics. I would start with "Industrial Heating", a trade magazine on line that deals mostly with heat treatment of metals. this article is interesting reading http://www.cryogenictreatmentdataba...chilling_toughens_metals_increases_tool_life/ . it details the use of cryogenics in 1955.
http://www.cryogenictreatmentdatabase.org/ has tons of free articles and papers written on cryogenics.
 
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stezann

Well-Known Member
#59
Thanks guys.
The storage issue is worth taking note! I have to find a dealer in my area, but i'm sure that relying on a longer shelf life is a no brainer regarding the choice of the cooling medium (maybe the price gap also?). So maybe LN could be overkill for 14c28n and probably is, but ramping down for the short time needed for complete martensite transformation won't hurt even if the temperature is lower than necessary.
 

KenH

Well-Known Member
#60
*Nickel is so effective in stabilizing austenite that it is the element that is used to make austenitic stainless which is always completely austenitic and non-magnetic, even at room temperature.
Now that is interesting - am I to understand it's the amount of nickel in non-magnetic stainless (like 316, 304 SS) rather than the amount of chrome?

Checking 304, 316, 410, and 416 SS I see the amount of chrome is in the 10%-14% range for all of them, but the nickel is only 1% range for 410SS and 416SS Ni is .01%. while for 304 Ni is 8% to 10.5% and 316 Ni is 10-14%.

I'd never really given it much thought what caused the non-magnetic property of SS. Until knife making 304 and 316SS were the primary SS I worked with and always considered magnetic SS as "low grade" SS because it was magnetic. Just goes to show how little I knew at the time.

I just keep learning from this site due to great folks sharing knowledge. They keep telling us old folks to work crossword puzzles to exercise the brain - me, I'd rather keep learning new things.

Ken H>
 
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