scope:

"Tiger stripes" on a high speed pinion made of carburized SAE 9310 steel were investigated. The stripes were on lines of action on the load side of the teeth coinciding with different angular positions of the gear mesh. Scanning Electron Microscopy (SEM) of the affected areas showed fused metal particles, with a diameter of 1-3 microns, and gas pockets. The morphology of the damage was typical of electric discharge damage shown in ANSI/AGMA 1010-E95. This indicates that the stripes were in fact electric discharge damage. Microhardness surveys on a metallurgical transverse section of a tooth showed a hardness loss due to the discharge, with load side surface hardness even lower than 58 HRC. The cause of the "tiger stripes" and potential damage to the gear tooth were analyzed.