1. Mechanism and improvement of the rolling contact fatigue of the surface layer with heterogeneous microstructures of the rail steel treated by laminar plasma jet.
- Author
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Peng, Keming, Yu, Deping, Zhang, Peng, Xue, Jiaqing, Li, Qinpeng, Wu, Ganyang, and Li, Lu
- Subjects
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ROLLING contact fatigue , *PLASMA jets , *ROLLING contact , *MICROSTRUCTURE , *CYCLIC loads , *STEEL - Abstract
• High cyclic tensile stress is the reason for the RCF damages in LPQ prepared hardened spots. • LPQT can prepare discrete hardened spots surrounded by transitional zone. • The transitional zone helps to alleviate the RCF damages in the hardened spot by decreasing the cyclic tensile stress. • RCF and wear resistances of the LPQT treated rail steel can be balanced by decreasing the transitional zone's thickness. Surface layer with heterogeneous microstructures (SLHM), characterized by hardened spots discretely embedded in a soft substrate, can be prepared by laminar plasma quenching (LPQ) to improve the wear resistance of the railway rail. However, severe rolling contact fatigue (RCF) cracks and spalling would occur in the hardened spots that only consist of quenched microstructure. This study analyzed the RCF damage mechanism of the LPQ prepared hardened spots by contact simulation. To improve the RCF resistance while maintaining the high wear resistance of the treated rail, a novel SLHM, whose discrete hardened spots are surrounded by transitional zone with the hardness lower than that of the quenched zone but higher than that of the substrate, was proposed and prepared by laminar plasma quenching-tempering (LPQT). Then, twin-disc tests and contact simulations were conducted to investigate the wear and RCF resistances of the LPQT treated rail steel. Results showed that the cause of the severe RCF cracks and spalling at the entry side of the LPQ prepared hardened spots was that the cyclic tensile stress at the entry side was always higher than that at the exit side under the cyclic rolling contact loading. The high tensile stress at the entry side of the LPQ prepared hardened spots resulted from the elastic deformation induced by tensile plastic deformation of the neighboring substrate. When the thickness of the transitional zone was about 0.1 mm, the generation of severe RCF cracks and spalling was significantly inhibited in the LPQT prepared hardened spots because the transitional zone decreases the cyclic tensile stress at the entry side of the quenched zone. Besides, the wear loss of such LPQT treated rail steel was only increased by 18.1 % compared with that of the LPQ treated rail steel, indicating that the wear resistance of the LPQT treated rail steel was not significantly reduced. These findings are promising for designing the microstructure of the surface layer to obtain wear-resistant rail with high RCF resistance. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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