Investigation into the evolution of the microcosmic surface of bainitic wheel steel material suffering polygonal wear

Abstract

With the rapid development of high-speed railway, it is imperative to develop highly comprehensive wheel/rail materials to improve the safe and stable operation of trains. Even though bainitic steel shows excellent resistance to rolling contact fatigue (RCF), its wear resistance is not good enough and whether it is qualified for high-speed wheel materials still needs further investigation. Through conducting rolling wear experiment on carbide-free bainite (FCB) wheel steel, this paper observed the changes of the surface profile lines of the worn specimens regularly and the wear morphology in different stages, and analyzed the changes of the microstructures and hardness on the surface layer, in order to explore the formation of polygonization wear (PolyW) from the angle of the microcosmic surface of bainitic wheel steel. The research revealed that during the process of rolling wear, the nonuniform load caused by mechanical vibration could lead to the appearance of PolyW on the surface of the two-disc specimens of FCB wheel steel. Based on the surface morphology and size variations, three stages could be divided to explain the formation of PolyW: The incubation stage where macromorphology underwent cyclic changes, the development stage where PolyW appeared in some regions and the mature stage where PolyW spread all over the circumference. The wear mode in wave crests was mainly featured by oxidative wear and adhesion wear, and the one in wave troughs was marked by fatigue wear with wear rotations increasing, PolyW on the surface was exacerbated. Compared with wave crests, wave troughs had a larger slip ratio and the additional impact load, so the microstructures experienced severer deformation, the hardness increase was higher and the depth of the hardening layer was greater.