White etching cracks: A result of bearing failures

Bearings in large industrial gearboxes or drive train applications, such as paper mills, crusher mill gearboxes, lifting gear drives - or especially in wind turbine gearboxes - are often subjected to a wide variety of operating conditions that, under certain circumstances, may push them beyond their limits.
This may cause a bearing failure, resulting in what is often described as white etching cracks (WEC), sometimes also called white structure flaking (WSF).

What are white etching cracks (WEC)?

White etching cracks (WEC) are cracks within the microstructure of bearing steel. They are decorated by white etching areas (WEA) on the steel surface. White etching refers to the white appearance of the altered microstructure of a polished and etched steel sample.  

The affected areas consist of ultra-fine, nano-recrystallized, carbide-free ferrite, or ferrite with a very fine distribution of carbide particles. These areas appear white under an optical microscope due to their low-etching response to the etchant. White etching areas around cracks are 10%-50% harder than the surrounding unaffected microstructure.

What types of bearings and applications are affected ?
Spherical roller bearing_spalls

White etching areas (WEA) develop around cracks during overrolling. This means that WEC can be found not only in bearings that have failed prematurely, but also in bearings that have failed due to rolling contact fatigue (after a long running period). Because WEC are part of the crack networks in any failed bearings, they can be found in all types of applications, as well as in all standard heat treatments.

All types of applicationsAll types of bearingsAll standard materials and heat treatment

Industrial applications

  • Wind applications
  • Industrial gearboxes
  • Lifting gearboxes
  • Crusher mill gearboxes
  • Paper mills
  • Marine PODs
  • Compressors
  • etc.

Automotive applications

  • Alternators
  • Continuous variable transmissions
  • others
  • Tapered roller bearing
  • Cylindrical roller bearing
  • Spherical roller bearing
  • Deep groove ball bearing
  • etc.
  • Martensite through hardened
  • Bainite through hardened
  • Case carburized

SKF logo