Study On Evolution Of Microstructure And Mechanical Properties Of High-Speed Train Axle Box Bearing

In recent years,the train operation speed has been great improved,and the key components subject more and more severe service environment with the rapid development of Chinese high-speed railways.As a key component of the train travel system,the bearing subjects to the train body load during normal operation,the traction and braking load during acceleration and deceleration,and various dynamic impact loads.The failure of the bearing will seriously affect the safety of the train.With the continuous increase of the high-speed train(HST)service mileages and the localization development,the research and production of new axle bearings is an important task for the research institutes and railway related institutions.The inspection of HST axle box bearings indicates that the peeling failure of bearing outer ring material accounted for the highest proportion in bearing failure.Therefore,it is important to understand the evolution of the mechanical properties,the microstructure characteristics,and the rolling contact fatigue failure mechanism,which could provide reasonable suggestions for the localization of the bearing.In this paper,the mechanical properties,microstructure characteristics and rolling contact fatigue failure mechanism of the HST axle bearing outer ring material are studied based on the test data of the outer ring material with different operating mileages:(1)The composition,phase structure,and microstructure are obtained by studying the microstructure characteristics of the new bearing,1.2 million km(Mkm)and 2.4 Mkm of the bearing out ring material.The experimental study indicates that the material in the outer ring contact zone shows obvious grain refinement after 2.4 Mkm.Based on the theory of martensitic transformation and grain refinement theory,the grain refinement process and the influence factor are analyzed,which could provide data support for the localization of the bearing.(2)The hardness distribution characteristics,tensile strength,elongation anc friction performance of the bearing outer ring material with different operating mileages are obtained by testing the mechanical properties of the new bearing,1.2 Mkm,and 2.4 Mkm.According to the evolution of the outer ring material of the bearing outer ring,the mechanical properties are analyzed.The reason why the substantial decrease of the elongation in the bearing outer ring raceway material is obtained through the analysis of the fracture surface and the plastic strain accumulation theory.According to the nano-scratch test,the variation of friction property and the fracture toughness data of the bearing outer ring raceway material is obtained,which could be used for the evaluation of mechanical properties for the localization of the bearing.(3)We propose a rapid fatigue test method for rolling contact fatigue(RCF)experiment of the axle box bearing material.Through the dry friction in the pre-cracking method,fatigue microcracks are introduced on the surface of the rolling fatigue specimen,which would shorten the RCF crack initiation period of the bearing.After the pre-cracking,the bearing lubricating oil is added into the experiment system,and the slip ratio between the rolling fatigue samples is adjusted by controlling the eddy current reducer.The method provides an effective way for the rapid test of the RCF of the bearing.(4)The hardness distribution,peeling and crack propagation law of the bearing outer ring material are obtained,according to the rolling contact fatigue test data of the bearing outer ring material.We find that the crack propagation is affected by the contact stress and the cycles,and the crack distribution follows Gaussian distribution.Through the theoretical analysis of solid mechanics,the crack initiation angle,the critical depth of crack propagation and the deflection angle in the mixed mode are obtained.The critical state of bearing crack propagation is verified by the rolling contact fatigue test data of bearing materials.In summary,this paper studied the mechanical properties,microstructure characteristics and rolling contact fatigue failure process of the outer ring material of axle box bearing under different operating mileages by using theoretical analysis and experimental research.The crack initiation,propagation and failure process of the bearing outer ring material are systematically studied by the theoretical calculation.The research results have an important reference value for the localization of HST axle box bearing in the future.