Numerical Simulation Analysis Of Railway Rail Laminar Plasma Selective Quenching Based On Fluid-solid-thermal Coupling

With the continuous increase of train axle load and operating speed,the excessively fast rail wear rate has become a key factor affecting the service life of railway rails.Railway rail laminar plasma selective quenching is a surface hardening technology,which can significantly improve the fatigue and wear resistance of the rail surface and prolong the service life of the rail.Carrying out theoretical analysis of railway rail laminar plasma quenching can deepen the understanding of the quenching process and provide theoretical guidance for process optimization.First,based on the fluid mechanics control equation,the finite element method is used to calculate the numerical solution of the non-isothermal fluid flow when the high-temperature plasma impinges on the rail;then the heat transfer control equation and the fluid-solid-heat coupling mechanism are used to calculate the rail heat during quenching.Heat distribution and temperature dissipation in the affected zone.At the same time,a non-isothermal phase transformation kinetic model was established to analyze the dynamic transformation process of austenite,martensite and other metallographic structure contents in the heat-affected zone of the rail during the quenching process,and the latent heat of metal phase transformation and the temperature distribution of the heat-affected zone were considered.Two-way coupling interaction relationship.Then,by calculating the elastoplastic strain,temperature strain and phase transformation strain of the rail heat-affected zone,the residual stress distribution range and the stress gradient amplitude of the rail quenching zone are analyzed,and the correctness of the model is verified by the mechanical performance test.Finally,using the abovementioned laminar plasma selective quenching theoretical model,the input parameters of the thermal plasma jet are controlled to analyze the influence factors of the quenching process,and the influence of the thermal plasma jet on the spatial distribution and residual stress of the hardened layer in the quenching zone is revealed.Through the above analysis,this article has mainly obtained the following conclusions:the flow field is symmetrically distributed when high-temperature plasma impacts the rail,and the calculation efficiency of the model can be greatly improved by symmetrically simplifying the model;there is a high-pressure stagnant bottom layer at the center of the thermal plasma impact.In this range,the flow velocity is lower and the pressure is higher,and the distribution range is basically the same as the size of the hardened layer;there is a large velocity gradient in the flow field space,and the impact of laminar plasma on the rail will hardly disturb the area beyond the rail head,and the maximum disturbance range is about It is 45 mm.The heat of the laminar plasma beam is approximately Gaussian.The heat source of the laminar plasma can be simplified as a Gaussian heat source when the effect of the plasma jet is neglected;the quenching area mainly generates austenite when the temperature is raised,and the martensite and the hardened layer are mainly generated when the temperature is lowered.The rail surface is roughly distributed in a semi-ellipsoid,and the distribution range is closely related to the parameters of the laminar plasma jet.10 s before quenching,the heat-affected zone of the rail is subjected to severe alternating stress,and the stress level is basically stable after 100 s;the maximum residual stress in the quenching zone is about 570 MPa,and the maximum residual stress in the quenching center gradually decreases to the surroundings.