Microstructural Alterations in Rolling Contact Fatigue

Stress-induced, structurally altered regions of ball and roller bearings were examined by transmission electron microscopy. The sectioning procedure is described in detail. A dark-etched region on roller bearings of carburized 4620 steel contained banded areas which had little in common with the microstructure of the martensite elsewhere. These lined-up areas ranged from a few to ten square microns. Electron diffraction patterns of the deformed areas exhibit arcing, but it is uncertain whether these regions give a distinctive pattern. Electron micrographs indicate that light-etched areas on 52100 steel ball bearings have a structure similar to the dark-etched regions on the other bearings. Observable precipitates do not form at tempering temperatures below 900 F. Electron diffraction patterns do not have spots which identify these microbands. X-ray studies, currently in progress, should indicate whether or not the microbands have a preferred orientation.