Study On Low Temperature Fatigue Fracture Properties Of Steel Q355NHC For Bogies

With the rapid improvement of the running speed and operating areas of high-speed trains in China,especially in the low temperature areas,the actual service conditions of the train become worsen,so fatigue fracture accidents occur.As the main carrier member of the train,fatigue fracture has a great impact on the overall performance of the train at low temperature.In order to ensure the safe,reliable,stable and efficient operation of high-speed trains and improve the localization of high-speed trains in China,meanwhile develop train models for different working environments to meet the future development strategy of the country,So study the low-temperature fatigue fracture properties of domestic bogie materials and a series of basic mechanical properties are great significance.In this paper,the effects of low temperature environment on the impact and fatigue fracture properties of domestic bogie materials and the related crack growth rate are studied.The fracture morphology of the samples is observed by OM and SEM.And using the method of comparative study,the strength evaluation and theoretical analysis of the performance of the bogie material were completed.The specific research contents of this paper include:(1)The V-notch Charpy impact test at different temperature was carried out,and the anisotropy of the impact toughness of q355 NHC steel was obtained.In the test temperature range of-50°C~-60°C,the L-T orientation showed obvious low temperature brittleness,and the impact energy was abrupt,which was lower than the T-L orientation impact energy.(2)The metal static tensile test was carried out.The comparative analysis showed that different orientations had little effect on the tensile properties of Q355 NHC steel,and the low temperature significantly improved the tensile strength of the material.(3)According to the actual application requirements,the fatigue performance test for typical temperature,sampling direction,stress ratio and stress concentration factor is carried out.Based on the analysis of macroscopic fracture and microscopic morphology,the complete fatigue performance characteristics of Q355 NHC steel were established.(4)Through the fatigue crack growth rate test,the influence of orientation and stress ratio on the fatigue crack growth rate of Q355 NHC steel in different stages of the bogie and its theoretical explanation are studied.