A portion of two large spur tooth bull gears made from 4147H Cr-Mo alloy steel that had spalling teeth was submitted for evaluation. The gears were taken from a final drive wheel reduction unit of a very large open-pit mining truck. The parts had met the material and initial heat treat hardening specifications. The mode of failure was tooth profile spalling. By definition, spalling originates at a case/core interface or at the juncture of a hardened/nonhardened area. The cause of this failure was either insufficient or no induction-hardened case along the active profile. The cause was activated by a nonfunctioning induction hardening coil that did not or was not allowed to harden the midprofile of several teeth.
Lester E. Alban, Spalling Failure of a Spur Gear, ASM Failure Analysis Case Histories: Failure Modes and Mechanisms, ASM International, 2019, https://doi.org/10.31399/asm.fach.modes.c9001502
Download citation file: