Effect of Pearlite and Proeutectoid Ferrite on Crack Propagation in Hypoeutectoid Rails Considering Microstructural Deformation

Abstract

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 comment (PF%) and pearlite interlamellar spacing (Sq)) and crack propagation behaviors (crack characteristics and crack tip propagation modes) was explored using statistical analysis. The results indicated a higher PF% facilitated crack propagation at a smaller angle within the deformation layer, while also promoting more pronounced branching in the matrix layer. Among all crack propagation modes, propagation along PF exhibited the highest priority. Moreover, in the deformation layer, PF was stretched into plastic flow lines that served as grain boundaries, which can suppress the upward crack propagation. The reduction of Sq would decrease the degree of deformation, crack depth, and the proportion of transgranular propagation. Within the matrix layer, the rail steels with a lower Sq exhibited a notable reduction in the proportion of transgranular propagation, causing cracks propagation along pearlite lamellae with lower energy dissipation.

Keywords: rail, rolling contact fatigue, pearlite, proeutectoid ferrite, Crack propagation