The Effect Of Laser Dispersed Quenching On Wear And Contact Fatigue Life Of Wheel/Rail Materials

With the rapid development of high-speed and heavy-haul railway transportation,the wear and fatigue damage of wheel/rail becomes more and more serious.Laser surface treatment of wheel and rail materials is an advanced technology.Laser dispersed quenching forms laser hardening regions with regular arrangement on the surface of materials,which can not only avoid the formation of soft overlapping region by tempering effect,but also form the alternate structure of laser hardening zone and soft substrate.Laser dispersed quenching technology has a certain practical signification for improving the wear and rolling contact fatigue properties of wheel and rail material,which extends the service life of wheel/rail.In this study,laser dispersed quenching is processed on the surface of wheel and rail materials by a multimode cross flow CO₂ laser.The effect of laser power and laser quenching time on the surface hardness,surface quality and the depth of quenching layer of wheel/rail specimens was investigated.On the basis of the optimum laser processing parameters,three kinds of laser quenching spacing were used on the surface of wheel and rail specimens.Under the dry and water conditions,the wear and contact fatigue life of laser dispersed quenching wheel/rail specimens under the optimum laser processing parameters conditions were explored using a MJP-30A rolling wear and contact fatigue testing apparatus.The main conclusions are as follows:?1?When the diameter of laser hardening spot is 5mm and the defocus distance is 32.5mm,the optimum laser processing parameters is the laser power of 900W and laser quenching time of 0.6s.?2?With an increase in laser quenching spacing,the wear rate of wheel/rail specimens increases.When the laser quenching spacing is 0.3mm,the wear resistance is optimal and the wear decreasing rates of wheel and rail specimens are about 35.7%and 66.8%,respectively.With the laser quenching spacing increasing,the surface damage of untreated zone becomes serious.The damage transforms from slight spalling to severe spalling and the thickness of plastic deformation increases.Furthermore,the subsurface damage becomes serious.?3?The wear rate of wheel/rail specimens significantly reduces after laser dispersed quenching and average wear rate of treated wheel/rail specimens decreases by about 49.2%.The wear rate of single-treated wheel or rail specimen significantly reduces.However,the wear of the coupled one without laser dispersed quenching aggravates.The wear of treated wheel/rail specimens is relatively slight and the dominant wear mechanism is small pitting and slight fatigue crack.Small spalling accompanying with fatigue wear is dominant in the substrate region between two treated regions.Laser dispersed quenching can effectively enhance the plastic deformation resistance of wheel/rail materials and inhibit the crack initiation.Meanwhile,the treated region protects the adjacent substrate material,hinders the crack propagation,which improves the fatigue resistance of the wheel/rail materials.?4?Under the water condition,contact fatigue life of treated wheel/rail specimens and single-treated wheel specimen enhance by about 101.9%and 75.2%,respectively.However,RCF life decreasing rate of single-treated rail specimen is about 47.6%.The surface and subsurface damage of failure wheel specimen for the treated wheel/rail materials relatively alleviates,and small shelling pit appears on the substrate region between two treated regions,which significantly improve the.performance of preventing fatigue shelling.The fatigue crack is not found in the section of laser quenching zone.The fatigue cracks appear on the bottom of the small shelling pit in the substrate region.Moreover,the crack extends along the edge of laser quenching region in the internal substrate material.