The Effect Of Laser Dispersed Quenching On Rolling Wear And Damage Properties Of Rail

With the development of heavy haul railway,the damage of wheel/rail becomes more and more serious.Especially the crushing and side wear easily occur on heavy-haul curve rails,which have become important factors affecting the safety of railway transportation.Therefore,investigation on the service performance of laser quenching has important guiding significance for reducing the wear and damage of rail and extending the service life of rail.In this paper,laser quenching on rail surface with different quenching ratios and different quenching forms was carried out using the fiber laser(YLR-6000).Rolling wear and damage properties of untreated and laser treated rails were tested by MMS-2A rolling wear apparatus and MJP-30 A rolling wear and contact fatigue apparatus.The optimum laser quenching ratio and form of laser quenching on rail were obtained.The main conclusions of this paper are as follows:(1)After laser quenching,the microstructure of rail rollers was obviously refined,the surface hardness was greatly improved,and the resistance to plastic flow was enhanced.After the test,there was almost no plastic deformation in the quenching zone,and the plastic deformation in the untreated zone was also obviously suppressed.The wear resistance of rail was remarkably improved,and with the increase in the quenching ratio,the wear resistance became better.Proper quenching ratio on rail could effectively alleviate rail corrugation and reduce the wear rate of wheel/rail system.When the rail quenching ratio was 50%,the wear rate of wheel/rail system reached the lowest,which was reduced by 36.52%.When quenching ratio was greater than or equal to 80.4%,serious ploughing appeared on the surfaces of both the wheel and the rail.With the increase in quenching ratio,the fatigue damage of quenching layer was aggravated.In the quenching layer,cracks usually appeared on one side of the circumferential rolling direction and propagated toward the inside of the material at a large angle,and stopped near the substrate region.The length and depth of cracks in quenching zone were larger than those in untreated zone,which means that the damage of quenching zone was more serious.(2)Different laser quenching forms had great influences on rail rolling wear and damage.When the distance between quenching spots was smaller and the diameter of quenching spots was larger,the wear resistance of rail got better.Among all quenching forms,the grid-like quenched rail had the best wear resistance with the wear rate reduced by about 72.50%.As the distance between quenching spots increased and the diameter of quenching spots decreased,the rail damage became more severe,and small spalling pits appeared on the surface of quenching spots.Among the strip quenching forms,the grid-like quenching on rail caused the least damage,and only short cracks appeared at the "sharp corner" of the quenching layer.(3)Under the water condition,the rolling contact fatigue life of wheel/rail was reduced after laser quenching on rail.Different quenching forms presented little effect on the fatigue life of wheel/rail.The surface of the untreated rail was seriously damaged with spalling,and many spalling pits were connected together to form larger spalling.After quenching,small and dense spalling pits appeared on the surface of rail quenching zones,and large spalling pits appeared at the edge of a few quenching zones.The surface of the untreated rail rollers was crushed,and cracks interweaved into a network,which extended to the interior of the material.The rails treated with the quenching spot with the spacing D=0mm and the diameter ?=3mm or with the quenching spot with the spacing D=1mm and the diameter ?=8mm,the rail damage was serious,and there were spalling pits on the surface of a few quenching spots.Cracks penetrated the quenching zone,and propagated to the substrate region.The grid-like quenched rail was slightly damaged,and small spalling pits appeared on the surface of the quenched zone.Cracks propagated in all directions at the bottom of the spalling pit,and the crack propagation depth was small.