Research On Microstructures And Properties Of Weld Joints Of Rail And Frog With 316L Stainless Steel Transition Layer By The Technology Of Laser Cladding

The seamless connection of frogs and rails is an important guarantee for the development of Chinese railway industry.This paper introduces a connection method preparing 316 L laser cladding transition layer on the U-shaped groove of the frogs and the rails,then welding on the groove by the technology of manual arc welding,researching on the microstructure and mechanical properties of two kinds of welding samples.Based on the software ANSYS,the influence of process parameters on the temperature and stress fields of U groove by the technology of laser cladding was analyzed.The results show that during the multi-layer laser cladding,there was a process of accumulation of heat,increasing the inter-layer cooling time can reduce the amount of the input of heat to the substrate.With the increase of cladding speed and groove angle,the residual stress is increased,the residual stress will decreases with the increase of inter-layer cooling time.Then selected the appropriate process parameters,preparing 316 L laser cladding transition layer on the U-shaped groove of the frog and the rail,welded on the groove at last.After the preparation of the laser cladding transition layer,there was no thermal crack in HAZ of austentictic manganese steel frog and there was a phenomenon of carbon diffusion,there wass no martensite formation in HAZ of track steel analysed by Metallographic,X ray diffraction and SEM.The cladding layer has good metallurgical bonding with the substrate and the surfacing weld.The grain growth in the cladding layer is followed by the process of planar crystal,dendrite,and cell crystal.Through tensile test,hardness test,fracture morphology observation,the tensile strength of track steel by the direct welded is 814.5 MPa,after the preparation of the laser cladding transition layer,the tensile strength of track steel is 636.7MPa.The brittle fracture of austentictic manganese steel frog by the direct welded due to the existing of thermal crack,after the preparation of the laser cladding transition layer,the tensile strength of track steel is 659.3 MPa.The strength of both specimens can meet the performance requirements of rails and frogs welded joints.After the preparation of the laser cladding transition layer,in the track steel,the hardness of laser cladding layer is 231.7HV,than surfacing layer was increased by 17.2%.In the austentictic manganese steel frog,the hardness of laser cladding layer is 232.6HV,than surfacing layer was increased by 10%.The hardness of both specimens can meet relevant standards.