Evaluation of polygonization resistance of two wheel steels from full-scale railway wheels and small test discs

Polygonization of railway wheels poses a significant challenge for the wheel-rail system. Despite the evidence from engineering practices highlighting the substantial impact of material factors on the polygonization resistance of railway wheels, research in this field remains limited. This study investigates two types of railway wheels, namely non-alloyed and alloyed wheels, which demonstrate different polygonization resistance under identical operating conditions. It involves microstructural analysis and hardness testing for the matrix materials and plastic deformation layer (PDL) of full-scale wheel, twin-disc testing for wheel steels, followed by analyzing the PDL of test wheel discs. The findings demonstrate that the full-scale wheel and test wheel disc exhibit consistency in terms of polygonization resistance, PDL microstructure, and microhardness, suggesting that the twin-disc test can be employed for material comparison regarding polygonization resistance. In addition, the alloyed wheel was found to exhibit better polygonization resistance at the external region of the wheel rim due to its higher resistance to plastic deformation and wear, while it demonstrates poorer polygonization resistance at the internal region of the wheel rim due to its lower wear resistance. Furthermore, the wave troughs display significant plastic deformation, dynamic recrystallization, and strain hardening near the contact surface, indicating a higher slip ratio at these locations. In contrast, the wave crests predominantly exhibit these characteristics in the subsurface region, indicating that the wave crests experience impact loading.