Investigation of rolling contact fatigue damage behavior of a ER9 wheel tread in relation to surface microstructural evolution

In the present study, we systematically analyze the relationship between the surface microstructural evolution and rolling contact fatigue (RCF) damage behavior of the ER9 wheel tread. In the unfatigued zone (Zone A), where the shear stress was low, a thin plastic deformation layer with low hardness formed. The ferrite grains exhibited obvious plastic flow; however, these grains were not refined, and the cementite showed no significant fragmentation or dissolution. Additionally, the dislocation density remained low on the wheel surface in Zone A. Conversely, in the fatigue zone (Zone B), where the shear stress was high, a thicker plastic deformation layer with increased hardness developed. The ferrite grains in this zone were notably refined, and a substantial amount of lamellar cementite fragmented and dissolved, leading to a high dislocation density on the wheel surface. The severe plastic deformation in Zone B facilitated the formation of fatigue wear cracks on the wheel, which initiated the RCF crack in Zone B. Furthermore, the interface between pearlite and proeutectoid ferrite grains in the wheel accelerated the RCF crack propagation, ultimately leading to RCF failure.