03-06-2018, 02:03 PM
I agree with the posters that indicated brittle failure. Surface hardening processes make a hard surface and keep a ductile interior. But, the depth of the hard surface is dependent on time and temperature of treatment. At a point, the hardened portions are so deep that they leave an insufficient ductile portion, and this type of brittle failure occurs. I've seen similar failures in high speed gearing.