Interesting article (if you are a geek) on cryo treatment of gear steel and thoughts from an engineer with access to Google

[kcjaz]

So, in my typical SOP manner, I am diving deep down a rabbit hole on cryogenic treatment of gears set off by my intent to regear. I am no metallurgist but I am a mechanical engineer and what I do know is that metallurgy and heat treatment of alloys is more art than science. In my professional experience (pipe and vessels not machine design) I've seen a lot of issues and unintended results from various heat treatment methods. Details and the control of the process matters, a lot. While I do not challenge that cryo treatment of gears in theory improves their durability, what I am trying to figure out is by how much. I want to understand that because I think there is a risk you could screw up your gears if the process isn't done right. This article provides a little insight into this.

The punch line, for me anyway, is two things:

1. the process isn't all that complicated and there does seem to be consistency in the temperatures and times from different sources. This to me means that the risk of damaging your gears appears low as long as you go to a reputable place that specifically does this for automotive racing and offroad customers.

2. The improvement in the steel properties for cryo'd 8620 gear steel (the material Nitro uses for their gears) isn't huge. The article shows, cryo treatment actually reduces the ultimate tensile strength though proof stress goes up. This means that while the cryo treated material will break with slightly less stress, the amount of stress it takes to start the plastic deformation is actually higher. This is better for what these gears need to do. Interesting if you are a total geek. Cryo also makes the material harder/less ductile (which also means more brittle). This is the classic metallurgy trade off and makes sense. The gears would be designed with a factor of safety well under the ultimate stress value. With the improved proof stress, hardness, the treated gears should be longer wearing for what they need to do.

My conclusion is that, cryo treated is probably better for gear service durability/wear but not a lot better. If you have a local reputable company that can do it, and it isn't that expensive (I've seen $50 to $100), its in the category of it likely won't hurt and is probably better. For 99% of 200's getting regeared though, I don't think it will make any real difference. It would be super interesting to get the OEM material specs to compare to Nitro or other aftermarket gears.

Effect of Deep Cryogenic Treatment on the Tensile Behavior of AISI 8620 Gear Steel

www.ijtsrd.com

 

[Rgill]

Racing industry has been doing this for years. Not just drivetrain but engine parts as well. It is a inexpensive process with proven results. In SCCA club racing I have seen treated brake rotors have a visible difference from non treated in just one race.

 

[kcjaz]

Racing industry has been doing this for years. Not just drivetrain but engine parts as well. It is a inexpensive process with proven results. In SCCA club racing I have seen treated brake rotors have a visible difference from non treated in just one race.

yep. agreed. All I'm saying is that a 200 series LC is generally not getting beat on or driven like a race car. If it isn't convenient or you for whatever reason regeared but didn't cryo treat your gears, I wouldn't loose sleep over it.

If I can find a good shop near me, and keep the cost less than a couple hundred, I'm probably going to do it. I was mainly trying to convince myself that there wasn't a risk of unintended bad happening for the hope of marginal gain.

 

[Tommy Dwyer]

Informative research, thanks for posting

 

[ToyotaMatt]

 

[NoClue]

Nice info. I'd love to find somewhere to get the intermediate shaft (the shaft that connects the passenger side CV to the front differential) cryo treated.

 

[linuxgod]

Does cryo-treating change the break-in process for gears? The idea behind the break-in is to work harden them, as the metal actually gets stronger after a few heat/cool cycles.

If you strengthen a gear, what's the next component to potentially fail? I mean in fairness the gears are probably up there in terms of repair problems/cost (unlike, say, a CV axle where you might want that to fail instead of a gear tooth), but it's a worthwhile thought exercise anytime you change the strength of a component. Would you also want to cryo-treat the rear axle shaft, for instance?

I have to wonder if Toyota is not cryo-treating their LC/LX gears from the factory, they must have a pretty high level of confidence that they are durable. Obviously that doesn't speak to aftermarket gears directly.

I didn't treat mine, so I'll see if they hold up for 300k miles without issue, for whatever anecdotal future evidence that means.

 

[kcjaz]

Does cryo-treating change the break-in process for gears? The idea behind the break-in is to work harden them, as the metal actually gets stronger after a few heat/cool cycles.

If you strengthen a gear, what's the next component to potentially fail? I mean in fairness the gears are probably up there in terms of repair problems/cost (unlike, say, a CV axle where you might want that to fail instead of a gear tooth), but it's a worthwhile thought exercise anytime you change the strength of a component. Would you also want to cryo-treat the rear axle shaft, for instance?

I have to wonder if Toyota is not cryo-treating their LC/LX gears from the factory, they must have a pretty high level of confidence that they are durable. Obviously that doesn't speak to aftermarket gears directly.

I didn't treat mine, so I'll see if they hold up for 300k miles without issue, for whatever anecdotal future evidence that means.

My take is this: cryo treating doesn't make a huge difference in strength. In fact, the ultimate strength is lower for cryo treated gears. People often confuse strength and durability. The improvement is wear resistance is also not huge. Incrementally better but not game changing for most people. If you are building a race car, incrementally better might just mean the difference between winning and losing but what are you really doing with your 200. As far as break-in process goes, I doubt there is enough difference in material properties to say with confidence that you can go 1000 mile rather than 500 before first gear oil change. No one would want to take that risk. Im my mind the break-in period is really about letting the gears "get to know each other" and wear in together before that get full power and torque through them. I could see where too much hardness or wear resistance might not be good.

As you imply, if cryo made a huge difference, then why doesn't Toyota or Nitro do this? They don't even offer it as an upgrade option. Its relatively cheap to do, so why don't they? My guess is that from their perspective, there just isn't enough improvement to matter for most of their customers. There is also not enough improvement in metal properties that they can reduce material thickness and save cost either.

Your point on what fails next is always a generally valid question to ask. In this case, I'd say it would be the axles and u-joints but I suspect that these components are already the weak link, so making the diff gears "stronger" doesn't really change anything.

I

 

[OregonLC]

I thought the break-in process was to wear the two components to form a perfectly machined match rather than work-harden them. Run them easy for 500 miles, then dump the resulting flakes, clean the magnet and start afresh with clean fluid. I'd be surprised if a pinion/ring interface got to a temp where heat was affecting the metallurgy.

 

[linuxgod]

I thought the break-in process was to wear the two components to form a perfectly machined match rather than work-harden them. Run them easy for 500 miles, then dump the resulting flakes, clean the magnet and start afresh with clean fluid. I'd be surprised if a pinion/ring interface got to a temp where heat was affecting the metallurgy.

This article calls it work hardening so I’m gonna use that term because it makes me feel like a material engineer

How to Break In Nitro Ring & Pinion Gears and the Importance of Breaking in New Gears

www.stage3motorsports.com

Brand new gears do run hotter until they break in. In fairness I do think micro-meshing of the surfaces plays a part too

 

[TomEf]

I'm a materials scientist who works in the aerospace heat treat field.

In my opinion, this study did it wrong. The only potentially useful thing their approach could have is to stop any further transformation happening by cooling immediately post-temper instead of letting the part air cool more slowly. This could have even been detrimental as their data suggests, but there are a lot of variables they didn't report.

The most effective application I can think of for cryogenic treatment within the heat treat process is immediately post-quench, which could reduce retained austenite/maximize martensitic transformation. There's a fine balance there with part size and configuration, good quench technique, and getting the part into your cryo equipment (probably still covered in oil) though. Too fast and you can crack parts, which can be violent and dangerous with high strength carbon low alloy steels. Too slow, and the cryo step is just about pointless.

In conclusion: cryo treatment may or may not do anything good for you and it completely depends on the process which they probably won't share with you

 

[Somebodyelse5]

I am no metallurgist but I am a mechanical engineer and what I do know is that metallurgy and heat treatment of alloys is more art than science.

I promise the heat treat on 747 landing gear is more science than art…

 

[TomEf]

I promise the heat treat on 747 landing gear is more science than art…

Well, C5 landing gear isn't cryo-treated. Draw whatever conclusions you like.

 

[kcjaz]

I'm a materials scientist who works in the aerospace heat treat field.

In my opinion, this study did it wrong. The only potentially useful thing their approach could have is to stop any further transformation happening by cooling immediately post-temper instead of letting the part air cool more slowly. This could have even been detrimental as their data suggests, but there are a lot of variables they didn't report.

The most effective application I can think of for cryogenic treatment within the heat treat process is immediately post-quench, which could reduce retained austenite/maximize martensitic transformation. There's a fine balance there with part size and configuration, good quench technique, and getting the part into your cryo equipment (probably still covered in oil) though. Too fast and you can crack parts, which can be violent and dangerous with high strength carbon low alloy steels. Too slow, and the cryo step is just about pointless.

In conclusion: cryo treatment may or may not do anything good for you and it completely depends on the process which they probably won't share with you

Awesome. So maybe there could be more benefit. 100% agree process and technique matter most. That’s the “art” part IMO.

 

[kcjaz]

Hey @TomEf, othe than potentially cracking parts which I would assume could only really happen if the part was a fair amount above ambient temp when put in the cryo bath, could you actually compromise the part in other ways with a poor cryo process? I might be willing to do it for the potential small benefits but not if there is real risk of damaging my new gears.

 

[TomEf]

Hey @TomEf, othe than potentially cracking parts which I would assume could only really happen if the part was a fair amount above ambient temp when put in the cryo bath, could you actually compromise the part in other ways with a poor cryo process? I might be willing to do it for the potential small benefits but not if there is real risk of damaging my new gears.

Where you're talking about sending them out to have it done, probably not any real risk. As long as the cooling rate is slow enough to avoid inducing any internal stresses, I don't think it could really hurt anything. If they're claiming it comes out of cryo harder than when it went in, I'd maybe be concerned about what has happened internally.

 

[Rgill]

This is a partial article on cryogenic in the racing industry.

By Roger Schiradelly and Fredrick Diekman.

Cryogenics Explained - Hekimian Racing Engines

The effects are an eye opener: By Roger Schiradelly and Fredrick Diekman. Racing pushes engine and drive train components to the absolute limits of their durability. Extending those limits means more speed, better safety, and more races won. For this reason Cryogenic processing is becoming a...

hekimianracing.com

Gears, shafts, and assemblies A study for the U.S. Army Aviation and Missile Command, by the Illinois Institute of Technology Research Institute concluded that cryogenic processing of the carburized 93/10 steel increase the gear contact fatigue life by 100%, and the ability of the gear to handle load by 10% over the same material that had under gone a –84 degrees C (-120F) cold treatment per Military specification. They also found that the conversion of retained austensite is only part of the effect on the gear. Most racing gears are 93/10 carburized steel, although 8620 is also used. It is interesting to notice that there is an experimental gear material under test that specifies cryogenic processing as part of its heat treat.

One major racing transmission maker, after inspecting numerous gearboxes after races, have asserted that cryogenic processing cuts the gear wear dramatically.

This also holds true for road racers of Porsches and BMW’s and other SCCA race cars who are now getting about three times the life on their gearboxes. The major problem of all these racers see is wear on the pitch line of the gear. Breakage is sometimes a problem, but that can usually be traced to driver error, bad heat treatment, or inferior material. Jerico Performance Products, a well know producer of Racing Transmissions, supplies gearboxes to over 50% of the racers in Winston Cup, and to many other racers. The company currently has all of its gears and shafts cryogenically processed.

Cryogenic processing also increases the other heavily loaded gears. We are doubling the life of ring and pinion gears and differentials, even under such severe usage as tractor pulls. Quick-change gears also show dramatic increases in life. Axle shafts, universal joints, and CV joints all show dramatic increases in durability. As the racing of front wheel drive cars becomes more popular, we begin to see more and more CV joints being processed, as this is one of the weak points of the drive line. Axles are treated to stave off fatigue failures in the splines.

Using extremely low temperatures to make permanent changes in metal and plastic components, cryogenic processing is not the typical –84 degrees C (-120 degrees F) cold treatment most heat treaters use. It essentially involves exposing materials to temperatures below –184 degrees C (-300 degrees F). If done correctly, it creates a permanent change to the material that alters many wear characteristics.