Cryogenic(sp) treatment

[brownshoe]

Per Cliff's comment: "This is supposed to be a science not a religion. The carbide contrast comes from a Journal article, which had materials testing on both methods."

When I was younger I was given the task of reproducing work published in scientific journals, most were peer reviewed. I found that at least 25 % of the time the work was not reproducible as written. Sometimes it would never work. As I grew older I found out that companies sponsor reserearch that is in their interest. Often times what is important in these types of articles is what isn't tested, covered or discussed. A lot of times the scientific design was superficial and the design was purpose built to give the results favorable to the sponsor. What I did learn, was that if I called up a reputable expert in the field, talked to them about what they did, had them direct me to reliable work, send me their procedures and publications, used these to find other reputable work that supported the initial studies, gathered more facts than I truly needed, then I found the truth. You won't find truth in articles, manufacturer's work sheets, or isolated researchers. You will find bits of truth, that when coupled with your finding people you can believe, will lead to the whole truth.

 

[Don M]

If anyone out there knows anybody who does better than Bob Dozier with D2, please step forward.

Which heat treatment works? The proof is in the pudding, folks.

 

[Cliff Stamp]

Mete, the process is well described as you have noted, however the central arguement given usually by the pro dep-cryo crowd is that the type of carbide changes structure wise. Specifically that deep cryo formes carbides which are much more wear resistant than multiple tempering.

I have seen numerous references in materials texts to their being different structures of carbides, and it isn't a great leap to assume that these could have different properties. Thus there is a basis for the cryo greatly enhancing wear resistance.

However what I have not seen is why deep cryo forms such carbides, and in general is there a significant change (crystal structure wise) of the three general types of carbides (pre soak, quenching, tempering). If there are, this would then mean the ablities of the steel would significantly be effected by variations in content.

Beownshoe :

I found out that companies sponsor reserearch that is in their interest.

Try looking at nutrition. You can find studies which indicate eating one way will kill you, and another study which argue that it is the best way for health.

The only way to proceed is to get enough of an education to check the logic in full detail, basically repeat the study. Or check for consistencies in the arguement and check by logical deduction based on known facts.

In regards to nutrition, the common reference are the well known population groups, however the variables are large and thus mistakes common.

Don, have you compared D2 by Dozier to other makers or manufacturers and found it to be superior in similar geometries? If so, which knives.


-Cliff

 

[Cliff Stamp]

Finally found the paper I read some time ago :

ISIJ International Vol. 34 (1994), No. 2, pp.205-210

"Role of Eta-carbide Precipitation’s in the Wear Resistance Improvements of Fe-12Cr-Mo-V-1.4C Tool Steel by Cryogenic Treatment "

Deep cryogenics induced the formation of eta-carbides by a sub-atomic movement, a non-diffusional process, these carbides are molecular in size.

This work is now generally accepted, and this paper constantly referenced. The work is being extended by many people, Ronald C. Lasky for example.

-Cliff

 

[mete]

Yes Cliff, and I have read the paper and I understand it . However when a rifle barrel maker ( they use 4140) references this it is a farce. But does eta carbide mean anything significant ? In a metallurgy book or on the internet you can find a photo of typical tool steel or knife steel ~ 1% or more carbon, taken at 1000x magnification. You will see carbides as white spheres - these are the major wear resisting carbides. You also create smaller carbides as you temper the martensite which are not visible at 1000x. These will add a lesser amount of wear resistance. And then you create even smaller carbides in deep freezing which add an even lesser amount of wear resistance. So my point has always been that yes you may form eta carbides by freezing but does it really add significant wear resistance ? Remember that Talonite blades get their great wear resistance not from anything in the matrix but the numerous large carbides.

 

[FK]

Mete,

Years ago I participated in Benchrest and varmint shooting with high tech rifles. We found the Cryo treatment did help with usefull barrel life, sometimes twice the amount of rounds could be fired before deterioration of accuracy. This is over the past 15 years with many hundreds of benchrest shooters. The barrels are also more stable and do not walk the center of impact compared to non Cryo treated rifles.

The steel commonly used for precision rifle barrels is 416 stainless not 4140 Chrome Moly.

The steel is heat treated as normal for the alloy and manufacturing process.

The early knife makers and metallurgy tests used the dunk method with dry ice and acetone at -100 degrees F approx. Bearing manufacturers use cryo treatment with liquid Nitrogen at -100 degrees F with 52100 and similar alloys for retained Austenite transformation.

The modern and well proven method is a -300 degrees F with a 20-24 hours cycle of slow temp drop hold and slow rise to ambient. The steel usually undergoes additional elevated temperature for post cryo tempering.

The metallurgy literature does not have much in techical details at -300 F however, the field tests are very positive. I believe more research has been done in Russia with Cryo treatment than in the West, apparently their documentation is not easy to obtain.

The USMC precision rifles for competition and scout snipers are cryo treated along with the McMillan stocks. It makes for a more stable synthetic stock and longer life for the barrel.

I agree with Cliff, the process is much more than retained Austenite transformed to Martensite. Why does women's stocking last significantly longer with Cryo, many musicians send their brass instruments for cryo treatment claiming sweeter sound. Something is happening at the atomic level??

Regards,
FK

 

[mete]

FK, The jury is still out on cryo for rifle barrels. Some makers say yes and some say no . For example LILJA says the only benefit is a POSSIBLE increase in barrel life. But to knives -again show me any significant increase in wear resistance due to freezing.

 

[Cliff Stamp]

mete :

So my point has always been that yes you may form eta carbides by freezing but does it really add significant wear resistance ?

It has been measured and found to be very significant, many times over. The form of carbides is also very significant to wear, not just the amount, as the hardness varies several times to one depending on the form and alloy content.

ASM, a pretty decent standard, reference this advantage to wear resistance, and specifically talk about the benefits of carbide formation by this manner as having benefits as opposed to precipitation on the primary carbides or along the austenite grain boundries.

To clarify though, I would not argue for knives that this advantage in wear resistance correlates to a similar direct advantage in edge retention. However cryo has other benefits such as allowing a higher hardness (usually 1-2 points), which will give a decent edge retention advantage depending on the knife.

-Cliff

 

[Bob Dozier]

Cliff

You need to know that I do not care one small amount what you belive but care what the knife customers think because they are my freinds and help make my living. So I do take the time to talk to you on the forums. Again, I'm not a metalurgist, same as you.

A question. When does the added hardness take place, before the temper or after? If before tempering, you will lose these points when you draw the steel back to the proper hardness to be used. If the steel is tempered back to the useable hardness and then deep frozen, will it get harder. I have other questions but will wait for your answer and would like a comment from our other knowledge freinds.

There is a tendency in some steels for austinite to stabilize after a time if it hasn't transformed completly. This will make cyro. not efficient unless it is done as soon as it is heat treated.

Give us a answer from your lips and not a copied answer from a cyro publication.

Bob D.

 

[Blop]

Originally posted by Cliff Stamp
mete :





However cryo has other benefits such as allowing a higher hardness (usually 1-2 points),

-Cliff

Hm, i´m not a metallurgist, but often listen to ones. Never heard this. I guess hardness allways varies about one point on knifes, depending on the balde shape (tthicker spine, thinner edge).

One advantage, i have heard of was, that stroping comes easier. Don´t know why.

I am not pro or con towards cryo. I guess nearly every manufacture does it more or less. Considering the possibilties of failed ht in "mass" production, i think it is quite right to do this. But i would say NO, if people start saying, this one was more freezed so it is better.

I have heard, -70°C is the max, where you get results. Anything deeper, makes no difference. So it will be up to us customers, not to cry to much for cryo, i mean the important part is named "HEAT - treatment". That must be done properly and cryo is the addition.

 

[Cliff Stamp]

Bob Dozier :

When does the added hardness take place, before the temper or after?

As quenched, it can be carried over into the temper with no loss of toughness, for references see posts on rec.knives by Alvin Johnson. I would be concerned about ductility* at a higher hardness, which is why in some cases this isn't an advantage which is why I noted that it depends on the knife. This however isn't the main advantage of cryo however, which as noted in the above is the increase in wear resistance due to the difference in carbide formation.

This will make cyro. not efficient unless it is done as soon as it is heat treated.

Yes, the above assumes it is done as part of the quench. If you do it after the knife has been tempered I don't think you would see much of an advantage at all based on what I have read. Some of the people selling cryo equipment will say otherwise, but I have not read any materials work showing large advantages to post temper cryo. There doesn't seem to be any arguement for it as cryo forming eta carbides is dependent on the high solubility of untempered martensite.

*I have not actually see it stated that ductility would be lower, I am just assuming it. Plus on larger knives edge retention takes a heavy back seat to overall durablity. While the extra hardness would allow a thinner edge, outside of a prototype knife I ingeneral would leave more slack for opps situations.

-Cliff

 

[Ed Severson]

The role of ETA Carbide report is to be taken with a grain of salt.
The information has been in question since its release and has never been duplicated or validated. In the tool steel sector its conclusions are not accepted as fact.

The main benefit to cryogenics is the conversion of retained austenite. Proper heat treatment can reduce the need for this process to zero depending on the alloy. The most common area cryo is used beneficially is in cutting tools made from high speed steel (which retains austenite readily). This is done to ensure dimensional stability as the cutting tools heat up during use.

ASM investigated cryogenics in depth and sponsored a short program at a Materials Solution Conference 4 or so years ago. Papers were given by tooling sources and Research groups on the effects of cryo on materials. To sum it up there is no conclusive evidence that cryo does anything magical. Crucible did tests in conjuction with a cryo supplier and tested various alloys for wear, impact toughness, bend fracture and hardness. Cryo was inserted at various stages of the heat treat cycle and compared to non-cryo'd material. The results showed no change due to cryo processing.

Cryogenics transforms retained austenite in steels. Anything else is unproven and not validated.

 

[Cliff Stamp]

Ed Severson :

ASM investigated cryogenics in depth and sponsored a short program at a Materials Solution Conference 4 or so years ago.

Do you have the details on this, are the proceedings and articles published. In 1995 ASM published "Tool Steels", which clearly promotes cryo as inducing significant advantages to wear resistance. The results of the above paper on wear resistance I have seen duplicated several other times in various journals. Has there been an article published challenging it?

-Cliff

 

[Cliff Stamp]

Here is a reference on the effect of cryo on hardness :


"...continuous cooling from an autenitizing temperature of 1750F down to -120F with no intermediate tempering or holding at room temperature results in an as quenched
hardness 2.5 to 3 Rockwell C points higher than if the quench is stopped at the room temperature." "In addition, increased strength is found at the same hardness level with no decrease in toughness."

from ASM's "Tool Steels" by Roberts and Cary. It is the last line that is of consequence.

I have used blades which have been heat treated in this manner by Phil Wilson, and even though they were very hard, they were not excessively brittle. He is using this method now to get 64/65 HRC on some of the carbon and 62/63 on stainless CPM steels. Reports are very good.

-Cliff

 

[Ed Severson]

The martensite finish temperature for most alloys is around 400 below and lower. The lower you can go directly from quench creates a finer martensite with higher hardness due to higher stress on the lattice.
The only concern with doing this is the potential for cracking. I have worked directly with Phil on this and he takes great care not to shock the blades when doing this. Just a word of caution for those wanting to do this themselves. In grades like A2 and D2 the little bit of retained austenite is good for ductility and removing it by cryo does drop the impact slightly but not enough to warrant too much conern. Roberts and Cary is an excellent book and I would recommend it for anyone wanting to know the basics of tool steels.

 

[thombrogan]

Were any of his >61RC successes done with S30V? I'd really enjoy seeing what that puppy does in the mid 60's in a Benchmade 921 or Spyderco Native.

 

[mete]

Ed, glad to see there is another metallurgist out there, and glad to see that you also are not impressed by the cryo hype.

 

[Bob Dozier]

Mete & Ed Severson

I have to go to work. I'm a little slow, and just realized that Cliff would have argued with Einstine about relativity. I'll let him pass, as it is not important. I realize that he has not ever been wrong on the forums and knows more than you professionals. I don't think that he realizes that you, Ed, are one of CRUCIBLE STEELS trouble shooters. If he swallowed a goat pill, he could fly like superman.
Good by Cliff. You are a cool guy with a lot of gall and I admire you to a certain point.

Bob D.

 

[donovan]

Originally posted by Bob Dozier
You are a cool guy with a lot of gall and I admire you to a certain point.

I'm going to make it my goal in life to have Bob Dozier say this to me some day.

Jack

 

[Cliff Stamp]

Ed :

I have worked directly with Phil on this and he takes great care not to shock the blades when doing this ...

I discussed exactly this with him a few years back after reading an article by Nu-Bit where they claimed that it was necessary to do a cryo treat via a slow cooling over 24 hours to prevent thermal shocking, they (surprise) sell equipment that does exactly this. Phil's cryo is done as part of the quench and a lot more rapid. He could have changed his process significantly since then of course. His knives are also very thin with extreme distal tapers so the volume to surface area ratio (important for thermal equil) is relatively very low.

So were the articles from the conference you referenced published. I would be interested in seeing published papers which support the ideas that :

1) eta carbide precipitation doesn't happen or does happen but isn't significant, as well out lining why the theory proposed in the above is wrong. Note the same theory is also mentioned in other materials works for other similar processes. For example NbC can also precipitate in the martix without regard to disolcations and can thus add to strength (Tool Steels, Roberts, Krauss and Kennedy).

2) the gain in hardness duing cryo doesn't happen, or does happen but doesn't allow a post temper gain of hardness, or does allow a post temper gain of hardness but does so with a corrosponding loss of impact toughness and/or ductility [if it is the latter it would still be of benefit on some knives].

These are the two published advantages to cryo besides the increased gain in martensite formation. Well there is one other element which is that cryo offers a finer grain size but it gets more complicated.

If the steel is subjected to multiple quenches, then the grain can be refined, the quenches give the finest grain structure when the intitial stage is untempered martensite, thus cryo can be used to get ~100% transformation but tempering can not before the next quench, Ref : "Heat treatment Shanghai, 1983", third international congress on Heat Treatment of Materials.

There is a point of contention here though because cryo and not cryo were not compared because cryo was used to prevent the martensite from cracking after quenching without having to be tempered. But it would seem sensible to conclude that if unquenched martensite gives the finest grain, then 100% would be better than 70%.

In grades like A2 and D2 the little bit of retained austenite is good for ductility ...

What about when it is transformed during temping or with cold working during use of the blade, it can then induces the precipitation of thin films of carbide along the grain boundries, "Steels ...", Honeycombe . These can be dealt with during secondary hardening if the transformation is during tempering, but why not avoid this by having a 100% martensite in the first place. Along that line why not simply due a 100% transformation and then tempered to achieve the required level of toughness, this would give a much more uniform composition which would be more stable.

Bob Dozier :

I don't think that he realizes that you, Ed, are one of CRUCIBLE STEELS trouble shooters.

Yes, I have talked to him before in email, he came up way back when I first started talking with heat treating with Wilson.

thombrogan, yes 62 HRC on S30V, even harder on S90V, harder still on 10V. The edge geoemtry is minimal, they cut very well, stay sharp for a very long time and sharpen very easily.

-Cliff