The fatigue performance of all high-strengthStrength steelsSteel is affected by internal defects. Primary carbidesPrimary carbides have been shown to be the main type of defects in M50 bearing steelsSteel used in the aerospace industry. Therefore, these steelsSteel must be characterized under service conditions, and their rolling contact fatigueRolling contact fatigue (RCF) propertiesProperties must be evaluated under different friction conditions. A method for analyzing the response of primary carbidesPrimary carbides is proposed; the RCF processProcess is further separated into a period of plastic instability and an elastic period. The accumulation of plastic deformation around the carbides before elastic deformation is proposed as the RCF damage parameter, and the influence of primary carbidesPrimary carbides is studied based on the damage criterion. The competition between surface and internal fatigue initiation is revealed through different coefficients of friction. A predictive model for RCF initiation is proposed, which could predict critical sizesCritical sizes for different types of primary carbidesPrimary carbides that are not detrimental to RCF performance, and critical sizesCritical sizes are calculated under typical industrial service conditions.