Cryogenic pistons

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Bryce418

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Just wondering what the experts think about cryo treating pistons.
I really don't know enough about metallurgy to have an informed opinion on wether or not it would help.
 
It usually can't hurt, but the benefits are not always clear, especially on alloys other than martensitic steels. Cryo will not make weak parts stronger, but it can make good parts even better, most often with respect to wear resistance and fatigue life.

I think you need to state what your application is to get a better answer. Street / strip / hardcore / etc.
 
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Well, what are you hoping the cryo will prevent? Are you making real light pistons that will be severely abused with gobs of rpm or something?

Obviously it won't help with melting....which seems to be a common failure mode...
 
cryo makes no difference with aluminum that we have seen. with steel some benifit will be seen.
 
nwpadmax said:
Well, what are you hoping the cryo will prevent? Are you making real light pistons that will be severely abused with gobs of rpm or something?

Obviously it won't help with melting....which seems to be a common failure mode...
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I was hoping you might have some input for me, I understand you may know a little bit about metalurgy:lolly:

I was mostly curious as far as benifits of cryo on aluminum in general. my limited knowledge of cryo treated benifits didn't include any on aluminum.


the question came up when a co workers friend was told by his machinist
that it was critical to cryo his pistons, but they also push cryo treated rods so I had some reservations about how critical it really was.

the pistons in question were for a cr cummins making 1000ish hp on stock 04 pistons.
 
OK, gotcha.

Maybe some clarification for your case.

If the failure mode is overheating and cracking, then cryo does you nothing. Duramax pistons went through similar issues (at generally lower power) and over time it became obvious that we were totally overloading and overheating what the part was designed for. The only answer is going to a stronger alloy and better design.

If you had them failing from pure fatigue (one definition of which is a part failing from cyclic stresses far below the yield stress)....then cryo might help. Note might.

The cryo crowd has a pretty good basis for its benefits in steels because it helps further the martensite transition to its fullest extent. Martensite is the phase which provides the most strength, so anything you do to further that will give you a stronger, more fatigue resistant material.

Aluminum alloys are generally strengthened by a precipitation reaction. You quench the alloy to trap the hardener in solution and then you reheat for specific length of time to bring out very fine, widely dispersed precipitates. I have not seen anything from the cryo folks on how a deep chill affects this type of hardening since you have to heat it to make it happen at all. Freezing it after that, not sure by what mechanism it helps.

The Nascar and NHRA folks are shaving everything down to be paper thin, to the point of fatigue failures in 500 laps, so there's probably benefit in it for them.

For you, seems like your money would be better spent on some forged units or monotherms. Then cryo them if you want them to last as long as possible.

One thing I can say, I have never heard of cryo hurting anything, so it's not like it's a negative. It's just a question of bang for the buck.

Hope that makes sense. The fix has to address the problem or it's a waste of time. And you can't pinstripe a turd.
 
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that is pretty much how I understood it based on my fairly minimal understanding of the process. I was sceptical after hearing your thoughts on cryo rods and that the person pushing for cryo pistons also pushes cryo rods.

I was amazed how little info the is on the net that isn't from somebody selling cryo treatment and I really have trouble beliving the information provided by them.
 
Bryce418 said:
that is pretty much how I understood it based on my fairly minimal understanding of the process. I was sceptical after hearing your thoughts on cryo rods and that the person pushing for cryo pistons also pushes cryo rods.

I was amazed how little info the is on the net that isn't from somebody selling cryo treatment and I really have trouble beliving the information provided by them.
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That's one of the reasons why the cryo folks still have some stigma attached to them like they're a "fringe" element. They are long on sales pitch and short on data.

That's not to say that data doesn't exist; there is some....but they need to publish more in peer-reviewed journals and such to get more respect.

Like for example....you hear all the time that it makes materials "denser". Now think about that for a minute. To make something denser, ya kinda need to shove the atoms closer together (or eliminate atomic voids, which is a whole subject unto itself). Show me how cryo does that, IRREVERSIBLY - i.e., warm it up and it should come back smaller than what it was to start with. I've yet to see anyone do that. Yet you read it all the time. So until someone shows me, I kinda regard it as marketing schmalz.

The second bad rap generator is the old "everyone in Nascar swears by it." Really. "But they won't share anything because it's top secret." OK.

More real-world data would do them a ton of good.

With cryo rods, you can explain the benefit rather easily - they're alloy steel and the effects on the martensitic phase is well known, AND rods are like the poster child for a part undergoing fatigue with fully reversing stresses (the worst case scenario). There was a guy a few years ago who had his OEM powder metal rods cryoed, hoping that it would help. He bent them in short order. Why? A) The alloy is not martensitic; all it did was make the rod cold for a while; and B) the design was far too small in the first place, they were being loaded somewhere between 2X and 3X the design load. Go figure.

As for the pistons, you could say that the pin bosses are under the same kind of fatigue nightmare and they are. So show me the fractured pin boss and I'll say maybe cryo would be a candidate for helping the situation. Maybe!

Show me a piston that's been Swoled, and I'll say that cryo would be about as effective as pissing on it!
 
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nwpadmax said:
Show me a piston that's been Swoled, and I'll say that cryo would be about as effective as pissing on it!
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I'm glad I wasn't drinking anything when I read this.. I really appreciate how you can make a informative post but still keep it funny.
 
but does cyro treating raise the melting point of the metal? or help it disperse heat better? ive always thought cyro treating was more towards stressed or contact parts.
 
chris lang said:
but does cyro treating raise the melting point of the metal? or help it disperse heat better? ive always thought cyro treating was more towards stressed or contact parts.
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edit: nwpadmax already answered that, i need to read better
 
chris lang said:
but does cyro treating raise the melting point of the metal? or help it disperse heat better? ive always thought cyro treating was more towards stressed or contact parts.
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Both of those properties are related to the nature of the atomic bonding in the metal, which I don't believe cryo could ever address.

Thermal conductivity and melting point are largely affected by the alloy content.
 
with the smoother grain with cyro would it raise the surface tension? if it does at all i dont think it would matter in the enviroment that pistons live in
 
I think coating the pistons would yield better results and be more cost effective.
 
chris lang said:
with the smoother grain with cyro would it raise the surface tension? if it does at all i dont think it would matter in the enviroment that pistons live in
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Cryo doesn't make "smoother grain" and has zero to do with surface tension. I'm not jabbing at you, just saying whoever told you that was waaaaaaaaaay off in left field.

X2 on the coating.
 
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