The slippage plays a more important role in microstructural modification of the pearlitic steel materials during rolling contact friction than the number of cycles. When a small slippage was used, the depth of the deformed layer was almost the same even with the cycles increasing from 103 to
105. However, when a large slippage was used, the maximum
depth of the deformed layer could be observed in a short
period of increasing cycle. Therefore, the degree of slippage decides the maximum depth of the deformed layer.