1. The microstructural details revealed transformation of retained austenite into un-tempered martensite under higher
internal shear stress.
2. The existence of internal stresses was validated by the DEA in the case.
3. Subsurface cracks developed within the altered orientation of laths in the tempered martensite by these stresses.
4. The variation in loading during rolling/sliding concentrated higher shear stress at the crack front and non-uniform fatigue
striations were produced in the crack propagation region followed by overloading.
5. The mode of failure was contact fatigue due to microstructural variations in the gear material.
6. The continuous rolling action of gears resulted in tooth bending which produced crack at the fillet root and followed the
path towards zero stress point.
7. The wide variation in hardness at the case and core resulted in the complete detachment of case after sever deformation of
core.
8. The excessive wear and removal of hardened case at driven gear teeth occurred by simultaneous rolling and sliding action
of meshing teeth of drive in the presence of debris and lost metal particles.