| Railway frog is a crossing equipment in the railway line, which is used to make the train wheels transform from one line to another line, it is also the most easily deformed part in railway lines. With the development of railway transportation, higher requirements are also put forward to the frog materials, and the bainite steel with excellent comprehensive mechanical properties has been considered to be the best material to replace the traditional high manganese steel. When the train passed through the railway frog, the cyclical impact from wheels may lead to a frog fatigue failure. A huge load will make different degrees of deformation to the frog over a long period, and it would make the railway bainite steel failure,even lead to incalculable consequences[1,2].So it is particularly important to improve the comprehensive performance of the railway frog.The material of the bainitic steel this study chose is a kind of Si-Mn-Cr material which has been researched and developed by xihua university department. In this paper, the influence of the heat treatment on overloaded railway bainite steel's micro-structure and characteristics of strain hardening properties after rolling contact fatigue were studied. Theoretical references would be provided for the production and practical applications of frog bainitic steel through the studying.The first,through studying the impact of austenitizing temperature and cooling way on micro-structure, hardness and toughness of overloaded railway bainite steel,and the micro-structure and properties of overloading frog bainitic steel were researched. The research results showed that the overloaded railway steel has the highest impact toughness which values of 75.4 J through air cooling,and the lowest impact toughness is 46.6J through furnace cooling in the same austenitizing temperature.The highest hardness of the overloaded railway bainite steel is 47.4HRC through air cooling,and the minimum hardness is 42.3HRC after the furnace cooling.Under the same cooling way, the hardness of overloading frog bainite steel decreased, and the impact toughness increased with the increase of the austenitizing temperature.The second,the rolling slip and the load to rolling contact fatigue properties of overload railway bainite steel were studied.Tests showed that the rolling contact fatigue life of overloaded railway bainite steel decreased gradually with the load increasing,and the contact fatigue life is much higher when there is no slip between the samples.It can be found that the mainly fatigue failure modes of overloaded railway bainite steel are shallow flaking and pitting flaking. The mainly damage form are pitting flaking and crack,and the propagation is generally discontinuous when overloaded railway bainite steel under 10% slip. The mainly damage form is shallow flaking and crack propagation is usually continuous when there is no slip.The third, the effects of compression ratio on deformation microstructure and properties of overloaded railway bainite steel were studied.The experimental results showed that the hardness of bainitic steel has improved significantly and the value of the hardness increased from 430 HV to 608 HV with the amount of deformation increasing. The equinoctial grain size of overloaded railway bainite steel gradually get squashed and elongate along the vertical compression direction after plastic deformation. With the increase of compression ratio, grainboundaries gradually disappeared, fibrous tissue formed and strip bainite gradually shred.The structure of overloaded railway bainite steel are mainly ferrite and austenite, a part of the retained austenite transformed into martensite.Through TEM observation, the lath bainite ferrite gradually narrowed and even bending fracture. With the increase of compression ratio,dislocations entangled and dislocation forest produced, dislocation were fixed pinning and impeded motion, the deformation resistance of overloaded railway bainite steel increased and hardening phenomenon performanced obviously. |
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