Effect of pearlite and proeutectoid ferrite on crack propagation in hypoeutectoid rails considering microstructural deformation

The evolution of microstructure influences rolling contact fatigue (RCF) crack propagation behavior. This study aims to investigate the effect of pearlite and proeutectoid ferrite on crack propagation in hypoeutectoid rails. The dry-wet alternation RCF tests were conducted using different hypoeutectoid rail steels to simulate crack propagation within the deformation and matrix layers. Subsequently, the relationship between microstructure characteristics (proeutectoid ferrite content (PF%) and pearlite interlamellar spacing (ILS)) and crack propagation behaviors (crack characteristics and propagation modes) was explored using statistical analysis. The results indicated that proeutectoid ferrite played a crucial role in determining crack propagation paths. Specifically, a higher PF% facilitated crack propagation at a smaller angle within the deformation layer, while also promoting more pronounced branching in the matrix layer. Crack propagation along proeutectoid ferrite exhibited a greater tendency, as evidenced by its proportion being approximately four times that of PF%. Moreover, in the deformation layer, proeutectoid ferrite was stretched into plastic flow lines that served as grain boundaries, which can suppress the upward crack propagation. The reduction of ILS would decrease the degree of deformation, crack depth, and the proportion of transgranular propagation. Within the matrix layer, the rail steels with a lower ILS exhibited a notable reduction in the proportion of transgranular propagation, causing the crack propagation along pearlite lamellae with lower energy dissipation.