determine if the crack is formed before or after carburizing process 2

[kevinthompson]

Dear all,
We have a cracked 8620 gear which is detected at the end of production line in crack detection.
the parts are supplied in forged&normalized condition.turning,teeth hobbing,spline cold forming takes place in soft condition.the parts are gas carburized and quenched then tempered.after hardening grinding the journals of shafttakes place.
I would like to understand if the crack was present before carburizing process(is already present on raw soft forging) or after carburizing(quenching or during streightening etc)
We are looking for decarburization presence at around crack which indicates if it was present before carburizing, if no, then the crack is posdibly formed after quench and fallowing operations.
I would like to ask supporting documents for this method from literature or technical documents.
Your comments are appriciated.
With my best regards

 

[TVP]

Some good references that describe quench cracking:

http://www.getottenassociates.com/pdf_files/6072_0192_224_web.pdf

http://www.asminternational.org/content/ASM/StoreFiles/05113G_Chapter2.pdf

http://www.smihq.org/public/publications/07_47_04/_technically_speaking.html