Peter wrote:
Amazing that < 0.001" of case hardening can do this. I thought the nitride layer was something like 0.025" thick and this is why e.g. camshafts can be reground without penetrating it.
My understanding is that the issue is with an outer layer on the surface of the thicker layer of nitriding, termed the white layer. If I understand it correctly, this article explains that the intent of the process is for the white layer to be removed by grinding to finished dimension after nitriding, and that as you say the remaining nitrided layer is thick enough to allow reginding. It is none the less amazing that such a thin layer can initiate cracks if not removed.
