Search Results

X-ray measurement is a very useful tool for bearing failure analysis. Compressive residual stress is created under the bearing raceway if bearings are used under a contact stress higher than the critical value. Residual stress distribution measurement of a used bearing enables to presume contact stress in service. Half height breadth of diffracted X-rey also changes with the fatigue of the material. Therefore X-ray measurement may estimate the degree of fatigue of a used bearing. Fracture surface of a fractured bearing has sometimes a high tensile residual stress at the surface, from which we can presume the fracture toughness of the material and then calculate the fracture stress. X-RAY diffraction is a very useful tool for bearing failure analysis, because X-ray diffraction technique can detect sensitively macro and microscopic lattice changes of a surface layer of crystalline materials.

Progress in the steel making process has improved the rolling contact fatigue life of bearing steels. Based on identical tests, conducted periodically over the past 20 years, improvements in the rolling contact fatigue life of through hardening bearing steels and various carburizing steels are described. Improvements in steel quality may alter the influence of various factors on rolling contact fatigue life, and because of this it is necessary for them to be re-examined. Based on recent test data, the influence of factors such as oxygen content, alloying elements, fibre orientation, steel making procedure and heat treatment factors such as microstructure and cooling speed during quenching on rolling contact fatigue life are described.

While rolling contact fatigue life of steels has been much improved by the improvement of cleanliness in steels due to progress in steel-making techniques, the demand for longer bearing fatigue life is ever-increasing. It will be necessary to find the best chemical composition and the best heat treatment conditions to further increase bearing fatigue life-Since bearing fatigue life also depends on the running conditions under which the bearing is used, it is also necessary to use material which meets the running conditions best. Carburizing steels generally have longer rolling contact fatigue life than through hardening steels. However, under debris contaminated lubrication such as in automobile transmissions, there were some cases where carburized bearings did not show such longer fatigue life.

Chromium and chromium-molybdenum carburizing steels are widely used for small- and medium- sized rolling bearings or gears, in Japan. Using a cylinder-to-ball type rolling contact fatigue rig, influence of various material factors such as chemical compositions, oxygen content, retained austenite and grain size in 1 % chromium carburizing steel was investigated. Life level of 1 % chromium steel has been increased gradually since 1968 when the test began. The increase in life level is mainly due to reduction in oxygen content by the improvement of steel-making technique. Manganese content increases the life and 1 % Cr steel with 1 % Mn has high reliable life. Prior austenite grain size does not seem to influence the rolling contact fatigue life.

Rolling contact fatigue lives of various steels used for medium- and large-sized bearings were investigated, using Φ60×ι90 specimen. Through hardened steels and induction hardened steels have nearly the same life, while carburized steels have lives about 3 times as long as that of through hardened steels. Since rolling contact fatigue life is affected by the cleanliness most significantly, it is most important to use clean steels for good bearing life. The influence of chemical compositions upon rolling contact fatigue life varied with cooling speed during quenching of the specimen. Using a steel which has excessively high hardenability for a small-sized bearing leads to a poor rolling contact fatigue life. For a medium or large-sized bearing we have to use a steel which has high hardenability necessary for the thickness of the bearing, but it seems unnecessary to pay close attention to the steel type.