Cryo treating

[Jackson1320]

I have everything to put together a spare shortblock. Im going to use stock boss rods. We all know that they are very strong for what they are. Now what about cryo treating them? Some say it is good for making them 10-20% stronger. Other people say it’s snake oil. What do you think?

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[Decible]

In theory it should help in metal fatigue by relieving stress. I don’t know that it’s any better than shot peening and magna fluxing to look for cracks. Or the cost difference.

 

[Jackson1320]

In theory it should help in metal fatigue by relieving stress. I don’t know that it’s any better than shot peening and magna fluxing to look for cracks. Or the cost difference.

When the temperature of metal drops -250 -300ish. its atoms rearrange in a manner that increases the metal’s martensite and decreases the metal’s austenite. Martensite is an incredibly hard crystalline structure, whereas austenite is soft

 

[engineermike]

Martensite is also very brittle. Many heat treatment processes aim to reduce martensite to improve material toughness.

I haven’t researched cryo treating much but it appears to marginally improve certain properties. Changes are dependent on the base material used, temp, soak time, etc. I would recommend searching for quantitative studies on the effects. I can say that it’s not widely used in industrial heavy duty applications.

 

[Jackson1320]

Martensite is also very brittle. Many heat treatment processes aim to reduce martensite to improve material toughness.

I haven’t researched cryo treating much but it appears to marginally improve certain properties. Changes are dependent on the base material used, temp, soak time, etc. I would recommend searching for quantitative studies on the effects. I can say that it’s not widely used in industrial heavy duty applications.

If they do the cryo-treatment right they first heat it and then bring it down to -250 to -300 for 24 hours and then when it comes out they reheat it again to complete the process. Sound right to you? I’m only looking for about 10% increase in strength, durability

 

[KeyLime]

If they do the cryo-treatment right they first heat it and then bring it down to -250 to -300 for 24 hours and then when it comes out they reheat it again to complete the process. Sound right to you? I’m only looking for about 10% increase in strength, durability

I'm a metallurgist and engineermike is spot on. You need to find info for the specific alloy and also identify the design limiting criteria. What's critical? Strength (yield or ultimate), fracture toughness, stiffness, corrosion resistance, stress corrosion, fatigue, etc? It's a complex problem and cryo-quenching might help something that's is/is not the problem, or help nothing at all.

Lots of smart materials and mechanical engineers wrestle with these issues every day and think they've got it all under control. Then one day you wake up, look at CNN, and see a B-777 limping along with a flaming engine due to fatigue in a fan blade.

 

[Jackson1320]

I'm a metallurgist and engineermike is spot on. You need to find info for the specific alloy and also identify the design limiting criteria. What's critical? Strength (yield or ultimate), fracture toughness, stiffness, corrosion resistance, stress corrosion, fatigue, etc? It's a complex problem and cryo-quenching might help something that's is/is not the problem, or help nothing at all.

Lots of smart materials and mechanical engineers wrestle with these issues every day and think they've got it all under control. Then one day you wake up, look at CNN, and see a B-777 limping along with a flaming engine due to fatigue in a fan blade.

So you’re opinion is that there isn’t a yes or no answer to if it will help or not and that there’s a chance that it could make the rods weaker. Correct?
Aircraft blades and laser peened. I would look into laser peening but it is very expensive

 

[KeyLime]

So you’re opinion is that there isn’t a yes or no answer to if it will help or not and that there’s a chance that it could make the rods weaker. Correct?
Aircraft blades and laser peened. I would look into laser peening but it is very expensive

First off, I'm sorry that what ever I say after this paragraph will sound so vague. It's a complicated problem and I don't have a lot of info to work from. But on the plus side the connecting rod cap bolt will likely be the failure point and nothing you do to the rod will matter.

I honestly don't know what the answer is. I also don't know why the rods fail. Side loading, compressive or tensile overload, fatigue? And what is your application? 500 hp at the crank? Who cares? 1200 hp at the rear wheels @ 9000 rpm...you're in a different world where every thing counts.

Let's just say I'm skeptical about someone saying that if they cool alloy X down to low temperatures the rods will last longer than a rod that isn't cooled down. Especially a 10-20% strength claim. And does strength correlate with lifetime? Where's the data?

If I don't understand the problem or the solution, personally I'd stick with OEM.

Second part of your question. I think you're asking if it can hurt. This is s a tough one. Granted, if it only costs $1.00 more per rod just do it, unless of course it makes things worse. Again, not knowing what alloy the rods are made of and having no data, anything I say is a wild ass guess.

 

[KeyLime]

Thinking about this some more. If fatigue is the failure mode for connecting rods there may be some benefit to cryo-quenching. As a general rule of thumb fatigue strength/life scales with ultimate tensile strength (UTS). If the cryo treatment truly raises the UTS (not to be confused with tensile yield strength) then there can be some benefit.

A simple, cheap test that is an indicator of UTS is a surface hardness measurement. If the vendor can show that hardness goes up after cryo treatment then he may be on to something. A hardness measurement on sample coupons should cost next to nothing and would be valuable data.

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