Subcase fatigue on a carburized gear. Photo courtesy GEARTECH © 2013.
Definition: Cracking in case hardened gears in transition zone between case and core.
Identification: Subcase fatigue results in the presence of fine longitudinal cracks and longitudinal craters with sharp, perpendicular edges.
Discussion: Subcase fatigue results when Hertzian contact stress exceeds the subsurface fatigue strength.
Prevention: Reduce Hertzian contact stress. Increase case hardness, case depth, and core hardness.