Research On Wear Resistance Of Bainite Rails For Heavy Haul Railway

Heavy-haul railway is the most effective way to improve the capacity of railway freight,and it is also an important development direction of China's railway.With the increase of axle load and transportation volume of heavy-haul railway,the problems of rail wear and rolling contact fatigue become more and more serious,but the existing rails in China cannot fully meet the requirements of use.The bainitic rail has attracted the attention of the domestic and overseas railway departments and research institutes because of its excellent strength and toughness.This study took the bainite rail produced by a domestic steel plant as the research object,conducted on the failure analysis of the bainite rail after field service,revealed the wear mechanism of the bainite rail,and systematically studied the relationship between the heat treatment process,microstructure,and conventional mechanical properties of the rail.Finally,rolling contact wear test was performed on the rails treated by different heat treatment processes to explore the key factors that affect the wear resistance of the bainite rail,and to provide the experimental and theoretical basis for the industrial production of a new generation of bainite rails.By analyzing the samples of bainite rail after operating on a small radius(R1000 m)curve of the Daqin heavy haul railway,it was found that the wear on the side of the rail is more serious than that on the tread.The wear on the tread of rail is mainly induced by the ploughing,and the wear mechanism is abrasive wear accompanied with adhesive wear.The wear morphology of the side wear is characterized by fatigue cracks and peeling,and the wear mechanism is mainly surface / subsurface fatigue wear.There are plastic deformation and work hardening layers beneath the wear surface of the tread and side of the rail.Through electron probe mciroanalysis,it was found that microcracks easily initiate in the segregation band caused by Mn segregation and propagate along the interface of the band.It is suggested that matrix microstructure and service conditions of the rail have a significant impact on its wear resistance.At present,the heat treatment process of rails is natural cooling + tempering after hot rolling,and the cooling rate is greatly fluctuant in the natural environment,which is not conducive to the improvement of rail wear resistance.Based on the phase transformation behavior of bainite rails and the on-line cooling conditions of the steel plant,8 different heat treatment processes(including 3 BAT treatments and 5 BQP treatments)were carried out.The microstructure and conventional mechanical properties of bainite rail steel after different treatments were analyzed,and it was found that,with the increase of isothermal temperature of BAT treatments,the strength and toughness of the bainite rails decreased,the volume fraction of retained austenite decreased,and the morphology of retained austenite was mainly blocky.The formation of blocy martensite/austenite(M/A)islands is not conducive to the improvement of the comprehensive performance of bainite rails.For the rail after BQP treatment,as the quenching and partition temperature increases,the strength decreases,but the morphology of retained austenite of the BQP is mainly film-like.Therefore,the overall mechanical properties of rail steel treated by BQP treatment is better than those of rail steel after the BAT treatment,exhibiting higher strength and toughness.The rolling contact fatigue test showed that the wear mechanism of rails after different treatment is mainly surface fatigue wear,and the abrasive debris generated by fatigue peeling also causes abrasive wear to some extent.As the transformation temperature decreases,the hardness of the rail gradually increases,the loss of wear decreases,and the wear resistance of the rail is improved.By comparing the loss of wear of bainite rail after different treatments,it can be found that the wear resistance of bainite rails treated by the BQP treatment is significantly better than that of the traditional BAT treatment.On this basis,a new bainite rail was trial-produced by BQP controlled cooling process.Compared with bainite rail produced by the traditional natural cooling + tempered process,the bainite rail produced by the BQP controlled cooling process has better wear resistance.