Effect of residual stresses on the crack initiation life for rolling contact fatigue

The life time of rollers in the hot rolling of steel was studied by analyzing the initiation and propagation of vertical short cracks due to rolling contact fatigue(RCF) in the backup roller steel.The studies used an optical microscope to trace the crack growth to analyze the effect of heat-treatment-induced residual stresses on crack initiation due to RCF.The results show that the short cracks initiate very quickly and initially quickly propagate at the beginning of the fatigue test,however,their growth stops after a few cycles.After a rather large number of cycles,the cracks begin to propagate in the circumferential direction and parallel to the contact surface for some cracks.The propagation behavior of these cracks is similar to that of long cracks.The propagation behavior of the vertical short cracks suggests that the number of cycles which reinitiates propagation of vertical short cracks can be taken as a criterion to distinguish the short crack from long crack stage of RCF.This criterion suggests that the measured ratio of the crack initiation time to the residual tensile stress and residual compression stress limits is 0.5～0.54,which is much greater than that the values(0.33～0.37) obtained theoretically.