TR6060 MAIN (OUTPUT) SHAFT FAILURE ANALYSIS

[Merc]

I just want them to replace it with a good one.

[mwt18]

Originally Posted by mwt18

Chemical Composition of TR6060 Defective main shaft (obtained from SPECTROMAX Spectrometer):

Attachment 247218

Anybody know what alloy this is? It seems to be between 8620 and 8630..

[mwt18]

Originally Posted by mwt18

Anybody know what alloy this is? It seems to be between 8620 and 8630..

Just posted the hardness data. That along with the chemical composition shows that this alloy does not match standards for any AISI 86xx steel.

It is likely that the shaft is made of AISI 8620 alloy, but was not carburized properly. AISI 8620 should have a carbon content between 0.180 - 0.230 %. The carbon content of the defective shaft averaged 0.27%. Higher carbon makes the material harder and also more brittle. There are also signs of quench cracks and inclusions in my sample. Not going to get technical here (unless there are people who actually care).


So, what does it all mean, man!?!
My professional opinion:
The root cause of the shaft failure was improper heat treatment. These defective shafts came from the factory with VERY small cracks and other internal defects. The cracks grow over time. How fast depends on the loading placed on them. The crack will eventually reach a critical length and the shaft will snap like a piece of chalk.

[Stex]

As an old 'heat-treater' of ferrous and non-ferrous metals, I would be interested in the process they used. They must be quenching in some warm media. Surely it is not design. Possible stress from machining that was not handled in the heat treatment?

[mwt18]

Originally Posted by Stex

As an old 'heat-treater' of ferrous and non-ferrous metals, I would be interested in the process they used. They must be quenching in some warm media. Surely it is not design. Possible stress from machining that was not handled in the heat treatment?

ASM standards require martempering for transmission shafts. It's a highly time and temperature dependent process. Can't say if residual stresses are a factor here or not.

The next test in the failure analysis is EBSD to map the grain structure. The machine is already booked by 'paying' customers, so it may be a week or two before they get this test done, but it should provide more insight.

[Mr. Notorious]

This is a great investigation, interesting on the carbon content.

[Huggerorange73]

If my trans hasn't been sent back yet, I'll snap a pic of it tomorrow.

[boostedyards86]

as for the poster above that is talking about footing the bill... i payed 5k for a trans from keisler when mine happened. My warranty was voided and I didn't have a transmission for 7months... Thats what happens when your in the first group of breaks.

[Huggerorange73]

Originally Posted by boostedyards86

as for the poster above that is talking about footing the bill... i payed 5k for a trans from keisler when mine happened. My warranty was voided and I didn't have a transmission for 7months... Thats what happens when your in the first group of breaks.

That really sucks....however the plus side is you no longer have to worry about your trans.

[Merc]

Had Pumpkin up on hoist yesterday, when I rolled the the rear wheels foward and backward a very noticable clunk was coming from the tranny. Any ideas?

[Stex]

Originally Posted by mwt18

ASM standards require martempering for transmission shafts. It's a highly time and temperature dependent process. Can't say if residual stresses are a factor here or not.

The next test in the failure analysis is EBSD to map the grain structure. The machine is already booked by 'paying' customers, so it may be a week or two before they get this test done, but it should provide more insight.

Interesting,figured thay were quenching around 350-400 F. Are they holding it there for awhile, then air cool?? thanks for the reply. Looking forward to more info when you have it..

[mwt18]

Originally Posted by Mercuryman

Had Pumpkin up on hoist yesterday, when I rolled the the rear wheels foward and backward a very noticable clunk was coming from the tranny. Any ideas?

Hmmm... Need more info. Your car does run, right? Was it in neutral? Could you tell if the clunk was coming from the tail end or was it inside the trans?

[mwt18]

Originally Posted by Huggerorange73

If my trans hasn't been sent back yet, I'll snap a pic of it tomorrow.

It would be very helpful and greatly appreciated!

[mwt18]

Originally Posted by Stex

Interesting,figured thay were quenching around 350-400 F. Are they holding it there for awhile, then air cool?? thanks for the reply. Looking forward to more info when you have it..

I'll scan and post some relevant info from the ASM Heat Treating Handbook later today.