ON WHITE ETCHING BAND FORMATION IN ROLLING BEARINGS

The problem of white etching band (WEB) formation in races of rolling bearings experiencing rolling contact fatigue is addressed in this paper. Neither the remarkable directionality of WEBs, nor the observed rate of their growth has been satisfactorily explained up to date. The previous attempts to explain the observed WEB orientation are critically reviewed. A new physical concept of WEB formation is introduced. It is suggested that diffusional outflow of dissolved carbon from WEBs, primarily caused by cyclic stress induced release of carbon segregated in the form of dislocation atmospheres, plays a fundamental role in WEB formation. Based on this concept, a dramatic improvement in the prediction of WEB formation rate is achieved (as compared to the previous analyses). The suggested physical concept leads to a new criterion of WEB orientation, involving maximization of the amplitude of variation of the deviatoric normal stress acting across the WEB, and taking into consideration the sequence of alternating stress extrema in a contact stress cycle. Peculiarities of the second of the two experimentally observed families of WEBs are discussed, and the new criterion is modified accordingly. The new WEB orientation criterion provides for the first time a consistent explanation of all basic features of the observed WEB directionality.