42CrMo4 QT 롤러의 구름 접촉 피로에 의한 표면 변화와 에지 로딩 손상 메커니즘

Abstract

This study comprehensively examines the evolution of surface damage and the failure mechanisms in 42CrMo4 quenched and tempered steel rollers subjected to rolling contact fatigue (RCF). The study conducts sys tematic fatigue tests using a dedicated RCF tester, which exposes specimens to up to 700,000 cycles under a con stant load of 7.5 tons and controlled grease lubrication conditions. The investigation employs confocal laser scanning microscopy and wear debris analysis to quantitatively assess the evolution of surface roughness, the ini tiation of microscopic damage, and the formation of debris throughout the fatigue life. The results reveal a distinct two-stage degradation pathway. First, an initial surface stabilization or “running-in” process occurs, characterized by significant flattening of surface asperities and a rapid decrease in average surface roughness (Ra) from approx imately 0.18 µm to less than 0.02 µm within the first 60,000 cycles. This is followed by a progressive stage of fatigue-induced damage, beginning after approximately 250,000 cycles, during which micropitting and a localized increase in roughness are observed. This transition indicates a shift from surface smoothing to a crack-driven mate rial removal mechanism. Notably, a distinct V-shaped pitting damage morphology consistently emerges along the edges of the rollers. This phenomenon is attributed to edge loading effects, which concentrate stress at the geo metric ends of the contact line, accelerating both crack initiation and subsequent propagation. These findings demonstrate that the fatigue durability of rollers is governed not only by early-stage surface stabilization but, more importantly, by the effective mitigation of local stress concentrations. The mechanistic insights provided in this study offer critical guidelines for optimizing roller profiles and alignment strategies, thereby contributing to the design of more durable and longer-lasting components in high-load rotating systems.