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Corrosion due to current leakage

Failure mode

Fretting wear, resulting from small-amplitude sliding and rolling at the bearing contact interface, manifests as either fretting (wear) corrosion or pseudo‑indentation; these two wear mechanisms are distinct.

Corrosion due to current leakage

Low current intensity

Near the shallow pit location

Chip grooves parallel to the rolling axis on the raceway and rollers are developed.

Turns dark gray

Failure mechanism

Initially, the surface is damaged by shallow pits that are closely interconnected; compared with damage caused by excessive current, these pits have a smaller diameter. This phenomenon can occur even when the current intensity is relatively low.

(Enlarged images: 500x, 5,000x)

Grooves are found on the raceways of both the inner and outer rings, not on the steel balls. The extent of the damage depends on numerous factors: current magnitude, duration, bearing load, speed, and lubricant.

A prime example illustrating the damage caused by current leakage in cylindrical roller bearings. Both the raceways and the rollers exhibit visible marks. Note the grease: in the early stages of this failure mode, the grease carbonizes, eventually leading to surface damage, spalling, and even seizure.

Under the microscope, we can observe numerous tiny pits on the surface.

Further magnification reveals the material’s microstructural changes. The white region has re‑hardened, typically exhibiting a hardness of 66 to 68 HRC. Beneath it lies a black layer that has undergone thermal annealing and is softer than the surrounding bearing steel (56–57 HRC).