Influence Of Machining Process On The Surface Performance And Micro-structure Of LZ50 City Railway Axle

LZ50 axle steel is currently widely used to build the axle of railway vehicles.The axle is an important component of the railway vehicle bogie,which is directly related to the carrying capacity of the axle and the safety of transportation.China is implementing a high-speed,heavy-duty railway transportation strategy,and the fatigue fracture performance of LZ50 axle steel is related to transportation safety.Therefore,it is of great significance to study the relationship between different processing technologies of LZ50 axle steel,and to study the new processing methods and processes.If we can use the effective surface modification method which can improve the fatigue performance of axle and extend its service life,which has important economic and social value.First carries on the analysis of surface integrity on the real LZ50 city railway axle,and then analyze what influence of different grinding,turning,surface ultrasonic rolling pressure process could do to the cross-section hardness of the axel,surface residual stress,surface texture,surface effect.Summarizes the regularity law of different ways of machining process parameters on the properties of axle steel surface contrast.Analysis between different surface processing methods advantages and disadvantages,selecting the optimal processing technological parameters.And that draw the following conclusions:the closer the axial compressive stress value of the axial end to the axial center,the larger the axle roughness value of the important part of the real LZ50 city railway axle,the surface axial residual stress is compressive stress,and the residual stress value of the axial and central axis is decreased.For the test sample of axle grinding,the bigger the size of the grinding grain,the smaller the rotational speed,the higher the surface hardness value of the axle,the deeper the hardening layer,water cooling reduces surface hardness slightly.The circumferential tensile stress of grinding axle steel surface is between 400 MPa and 510MPa.The smaller the grinding size,the less surface crack and the higher the processing quality.In the execution of the turning process,the higher the feed quantity and the lower the speed,the higher the surface hardness value,the deeper the hardening layer,among which the rotating speed was the most effective on the hardness distribution of sample surface.With the increase of the supply of the car,the axial residual stress of the axial sample was gradually reduced,and the stress of the residual stress increased.As the cutting depth and speed increase,the tensile stress of the axle steel surface increases.All the turning samples have a 1-2?m fine grain layer.The size of sub-crystal ferrite becomes larger significantly from the surface to the heart.The size of sub-crystal is between 100nm and 500nm,and which has a certain direction.The subsurface sub-crystalline transition becomes to Isoaxial fine grained tissue,and The carburization of the near-surface area has the fragmentation and obvious plastic rheological.When the surface ultrasonic rolling process is processed,the depth of the feed,the smaller the speed,the higher the surface hardness value of the axle,the deeper the hardening layer.Compared with turning and grinding,the surface ultrasonic rolling pressure is more advantageous to deepen the depth of the hardening layer and enhance the surface hardness.After the surface ultrasonic rolling pressure treatment,the surface axial residual compressive stress of the sample was 1?3 times higher than that of turning and grinding process,and the residual stress is converted to residual stress at the surface.It is a better surface performance of LZ50 axle steel after the surface ultrasonic rolling pressure treatment than that of turning or grinding.