It looks like a steel making defect, nothing to do with service. I remember seeing similar pictures of internal "bursts" in cold drawn bar. I can't say more, not my area of experience.

It looks like a steel making defect, nothing to do with service. I remember seeing similar pictures of internal "bursts" in cold drawn bar. I am seeing a fracture at 45 degrees to the axis making a cone-like surface. Bending fatigue would fracture at 90 degrees to the axis, torque fatigue would fracture in a spiral ; so that is why I can be certain it is not service related .