Originally Posted by
Concentric
@riff_raff: Thank you for that enlightening explanation of the carburizing and etching processes. It illustrates well the point I mentioned about complex processes required to achieve a safe finished product, and that is just one such process. Who would imagine that to control dimensions of the bearing raceway and hardened layer that so many chemical and thermal processes would also be required, some of which to counteract potentially harmful effects of a preceding process?
Concentric-
Glad to help. I found your question regarding potential hydrogen embrittlement of the planet gear quite interesting, so I looked into it.
It indeed seems ironic that an inspection procedure intended to detect material damage from a previous manufacturing process could itself potentially produce damage to the material. Also consider that the hydrogen embrittlement relief relies on strict adherence to a controlled process to ensure quality. This requires every person involved to maintain accurate documentation/records of their work. With the hydrogen embrittlement relief baking of these planet gears, even something as simple as how the gears are positioned in the furnace can be important.
Hydrogen embrittlement in steel parts is often associated with finishing processes such as electroplating. Copper plating (AMS 2418 type 2 or similar) is often used with carburizing to mask surfaces that don't require case hardening. The copper plate masking is sometimes removed after heat treat using a chemical stripping process. And plating specs (such as the one noted above) usually require the stripping method to be defined as part of the approved process, and state that the process shall not produce hydrogen embrittlement in the part. But as noted above, this only works when the controlled process is strictly adhered to by everyone involved.