Scheme Optimization Research On Laminar Plasma-Jet Surface Strengthening Of Switch Rail In Railway Turnouts

In order to reduce operating costs and improve transport efficiency,heavy haul freight has become an important direction of railway development.As the axle load of the train increases,the wear and damage between the wheel and rail becomes a technical problem that needs to be solved urgently.For parts with severe wear such as switch rails in railway turnouts,laminar plasma-jet surface strengthening technology quenches the surface of the rail to improve the wear resistance and prolong the service life.Therefore,the research on the laminar plasma-jet strengthening technology of switch rails in railway turnouts has important practical significance.In this paper,the laminar plasma-jet surface strengthening technology in switch rails is studied by simulation and field test for the purpose of optimizing the surface strengthening scheme.The effect of this technology on the tensile property,the wear resistance of rail materials and the wheel-rail contact force characteristics are analyzed.the optimization of the application scheme is proposed based on the simulation and test results.The specific conclusions are as follows:(1)The results of tensile test and static bending test show that the laminar plasma-jet strengthening technology reduces the tensile strength of rail materials by about 30%,but the strengthened rail still meets the requirements of the specification for static bending performance.(2)Finite element simulation analysis of laminar plasma-jet strengthened switch rail was carried out.Strengthened area results in redistribution of contact stress on the surface of switch rail.Although Von Mises stress increases significantly at the strengthened area,the overall plastic strain level of switch rail decreases with the increase of yield strength.Von Mises stress extremum increases with the increase of strengthened area diameter and decreases with the increase of thickness,while plastic strain extremum decreases with the increase of strengthened area diameter and increases with the increase of thickness.The spacing of adjacent strengthened area should be greater than 2 mm,so that they will not affect their respective stress and strain distribution.(3)The wear resistance of strengthened rail material was analyzed by rolling contact fatigue test.The wear resistance of laminar plasma-jet strengthened specimens is significantly higher than that of common specimens.The wear resistance of the specimens increases with the increase of the proportion of strengthened area to the whole surface,and first increases and then decreases with the increase of diameter.The optimum wear resistance is achieved when the diameter is 5 mm,and 5 mm should be taken for strengthening scheme,and the proportion should be based on the value of diameter and spacing of strengthened area.The strengthened area of the material is uniform and compact martensite with high hardness,which can effectively restrain the plastic deformation,pitting and delamination of the material surface.The cracks at the edge of the strengthened area did not propagate to the surrounding base material area.(4)Field application observation shows that under the same operating conditions,wear resistance and service life of the laminar plasma-jet strengthened switch rails are much higher than those of the untreated ordinary switch rails.Damages such as pitting and cracking appeared in some strengthened switch rails,which have not affected their normal use,and the service life could be further prolonged by timely eliminating the damage by grinding and other means of maintenance.