Effect of Microstructure on Rolling Contact Fatigue of Bearings

There has been proposed an innovative thermal treatment of bearing steel 100CrMnSi6-4, where the existing standard heat treatment has been replaced by austempering. The structure of low-temperature tempered martensite has been replaced by a microstructure composed of martensite and lower bainite with midrib. The kinetics of bainitic transformation and isothermal martensitic transition at selected austempering temperatures was controlled by acoustic emission. The research on contact strength was made under the conditions of rolling-sliding friction. The microstructure was revealed with the use of a light microscope and the forms of pitting wear were displayed by a scanning electron microscope. It was found that the optimum microstructure providing the best used contact strength of the tested steel is conditioned by the formation of a lower bainite with midrib at the temperatures near MS. A plausible cause of the increased resistance to pitting is bifurcation of fatigue cracks on dispersion bainitic carbides in combination with primary carbides, in bainitic-martensitic matrix.