Gear failure (nitrided gear). Please give insight!!!

[EngineerDave]

I am working on a failure analysis in the metallurgical lab.

My question to the gear gurus is the following: In a nitrided gear, is there any reason why it would be desirable for the nitride pattern or depth of nitriding pattern to be anything other than uniform around the profile of the gear teeth?

The profile I'm finding is deep on the leading edge of the tooth and very shallow on the trailing edge. I will post dimensions when I have them. This is not what I normally would see for carburized gear teeth and I suspect it may have some role in the failure.

The failure was noted during manufacturing, not during service of it.

Any advice would be greatly appreciated!!!

 

[Carburize]

Most unusual! Do you know how the gear was nitrided, i.e. conventional gas nitriding or plasma?
Typically nitrided gears are only lightly lapped to remove any white layer.

 

[EngineerDave]

I believe it was conventionally treated, but more details developing.

It is apparent that the cracking that appear mid pitch on several teeth was present before nitriding, as the white layer has developed along the surface of the crack as well.

Current opinion is that it might be a forging lap in the raw material.

Not to sure myself yet.

 

[GearmanPE]

No reason to desire thinner case on one side than the other.

This is a problem with the process. The case is always desired to be uniform all around.