| The rolling contact fatigue behavior of 52100 bearing steel has been the subject of study on numerous occasions in the past, but the complete mechanism underlying fatigue behavior has not been fully characterized. Specifically, past research has failed to establish with experimental support the origins of residual compressive stresses that arise due to rolling contact. Therefore, this research will be directed towards identifying, experimentally proving, and characterizing the compressive residual stresses that are due to retained austenite transformation in 52100 steel bearing balls.; The theoretical phase of the research presents a linear model indicating the amount of residual stresses that are expected to originate from retained austenite decomposition. The model was developed using the strain that the lattice experiences upon retained austenite's transformation to martensite. The experimental phase of the research consisted of a series of retained austenite and residual stress measurements taken by means of x-ray diffraction and coupled with optical metallography. By collecting x-ray diffraction measurements 180° from the rolling direction, this study identified successfully the factors affecting changes in residual stresses during rolling contact.; Results of the x-ray diffraction measurements of retained austenite showed that balls transformed, on average, 2.08% of their retained austenite prior to spalling. Based on theoretical calculations, a change in residual stresses induced by retained austenite transformation should be observed in the order of −8.505 ksi. Residual stress measurements taken from the direction opposite to rolling produced the same readings as the ones obtained from the rolling direction. This confirmed an important conclusion of this study: that most changes in residual stresses are due to microstructural transformation and not strain hardening, since psi-splitting did not occur. Lastly, even though overall the balls' surface was in a condition of compressive residual stresses, relaxation of the residual stresses in the order of (tensile) 45 ksi occurred during rolling contact. This deviation from the expected change in the magnitude of residual stresses in the worn tracks is, this study concludes, the result of the fact that any increase in compressive residual stresses that resulted from retained austenite transformation was offset by crack propagation due to overrolling. It is recommended that, in the future, this experiment is repeated with bearings balls that have been rolled only to the number of cycles required to complete retained austenite transformation. |
