Keynote Speaker
Prof. Ruiming Ren
School of Materials Science and Engineering, Dalian Jiaotong University
E-mail: rmren@djtu.edu.cn
Title: Nanostructured White Etching Matter Formation Mechanisms due to Rolling Contact Fatigue in Bearings
Profile:
Ren Ruiming, Ph.D., is a professor at the School of Materials Science and Engineering, Dalian Jiaotong University, and vice chairman of the Chinese Society for Heat Treatment. He used to be the vice president of Dalian Jiaotong University. He has been rated as one of distinguished professors in Liaoning Province and the leader of the provincial innovation team of key materials for rail transit. He has presided over and participated in a number of projects, including the national major 863 project and 973 project, and has created a new research field on the evolution of the microstructure and properties of metallic materials in the process of wear and contact fatigue, and provided a theoretical basis for the design and life extension of wheel-rail and bearing steel materials. At present, the main research fields are metallic wear and contact fatigue, anti-fatigue manufacturing of axles and bearings, etc. He has published more than 200 papers, including 70 SCI-indexed publications.
Abstract:
In this paper, scanning electron microscopy, transmission electron microscopy and nanoindentation were used to systematically analyze the nanostructured white etched structures in the insulated bearings of the high-speed rail in the lower line, and two types of nanostructured white etched structures with different microscopic characteristics and properties were found. Combined with the service conditions, microstructure and performance characteristics, the formation mechanism of the two types of white etched microstructure is discussed, and it is concluded that one of them is formed under a single large contact load and strain, and the other is formed under a lower load and strain and a high fatigue cycle, and the latter has finer grain size and higher hardness. Combined with the experimental observations, the uneven carbon content of ordinary high-Cr bearing steels, the characteristics of mixed martensitic microstructures and the martensitic phase transition theory, a "soft zone model" was proposed, which preferentially formed in the martensite region of the original austenite grain boundary slats. Through experimental measurement and finite element simulation, it is concluded that once the plastic deformation of the low-strength "soft zone" occurs under fatigue load, it will cause the microscopic residual stress change of the deformed area and the surrounding slightly high-strength matrix, and the residual stress and external load work together to make the "soft zone" continue to undergo plastic deformation, secondary carbide and tempered carbide dissolve, and martensitic slats continue to refine until they reach the nanometer level, and at the same time, its hardness can reach nearly 3 times the average hardness of the matrix. This theory can satisfactorily explain the experimental results such as the irregular distribution characteristics of white etched microstructure and cracks, the formation of white etched microstructure before cracks, and the hardness of white etched microstructure is significantly higher than that of the matrix, and provides a theoretical basis for slowing down or even inhibiting the formation of white etched cracks that cause early bearing failure.