2026-10-12T04:45:40Z https://www.scidb.cn/oai

10.57760/sciencedb.Tribology.00055 2026-06-22T15:39:37Z

2026-06-22 Microstructure and Properties of the Contact Surface Layer of U20Mn Bainitic Rail Steel under Rolling/Sliding Conditions doi:10.57760/sciencedb.tribology.00055 en This study aims to provide a deeper understanding of the rolling contact fatigue (RCF) damage mechanism in U20Mn bainitic rail steel. Fatigue-wear experiments were conducted under controlled rolling/sliding conditions using an HPJ-1G rolling contact fatigue and wear testing machine. A comprehensive investigation involving systematic microstructural characterization and mechanical analysis of the near-surface layer of the tested specimens was performed to elucidate the underlying damage mechanisms and key influencing factors. The experimental results demonstrate that after 200 000 rolling cycles under a contact stress of 1 000 MPa and a slip ratio of 0.4%, the material's wear rate and the residual stress on the contact surface stabilized at approximately 1.92 μg/r and 663 MPa, respectively, indicating a transition to a steady-state wear regime. A pronounced plastic deformation layer, approximately 100 μm in thickness, was formed beneath the contact surface. Within this layer, fatigue cracks were observed to preferentially initiate and propagate along the metal flow lines, which delineate the direction of severe shear deformation. Detailed microstructural analysis revealed that the surface transformation under cyclic rolling/sliding contact is predominantly governed by intensive dislocation activity. The motion and reorganization of dislocations progressively subdivided the original bainitic ferrite laths, leading to the formation of dislocation cells. These cells subsequently evolved into new grain boundaries with high misorientation angles, culminating in significant grain refinement. Quantitative assessment showed that the number of grains per unit area increased remarkably—by a factor of about seven compared to the untested matrix. This refinement process was accompanied by substantial work hardening, resulting in a microhardness increase of 18.58% relative to the base material. Furthermore, advanced microstructural characterization techniques confirmed the development of a distinct shear deformation texture aligned parallel to the {111} crystallographic planes in this refined region. Energy-dispersive X-ray spectroscopy (EDS) also indicated noticeable carbon enrichment at the newly formed grain boundaries, suggesting carbon migration during the deformation process. A comprehensive analysis of these findings confirms that the microstructural evolution in the near-surface region of U20Mn bainitic rail steel under rolling/sliding conditions is the direct and primary factor governing its wear resistance and contact fatigue performance. The stability and evolution of this surface-affected layer are intrinsically linked to, and constrained by, the initial multiphase microstructure, which consists of bainitic ferrite laths, retained austenite films, martensite, and martensite-austenite (MA) islands. The insights gained from this work contribute to a more fundamental mechanistic model for RCF damage in advanced rail steels and provide valuable guidance for the future development of bainitic steels with enhanced service life and reliability under demanding railway operations. U20Mn bainite rails; rolling contact fatigue; plastic deformation layer; microstructure; wear performance GAO Chao Zhou Yulong Wang Jichuan Wang Dongmei Bao Xirong Cen Yaodong Chen Lin PUBLIC https://creativecommons.org/licenses/by-nc-nd/4.0/ dataset Science Data Bank