A Study On The Surface Microstructure And Property Evolution Of Wheel And Rail By Ultrasonic Impact

In this paper,microstructure features in the surface layer and hardness of the samplers are systematically characterized by using optical microscope,scanning electronic microscope,transmission electronic microscope,microhardness testing machine and surface roughness testing machine.This paper first analyze the surface and hardness of the ineffective freight rails,and from the results we learned that the main damages on the wheel surface are stripping and spalling,which are caused by the uneven load.The white layer was formed on the wheel surface at the same time.Major damages on the wheel flange are badly worn,and white layer was also formed on the surface of the wheel flange.The hardness test show that the hardness of white layer area increased three times compared with before.Then ultrasonic surface strengthening impact is acted on the heavy load wheel steel,rail steel and pure iron.The result shows that after different ultrasonic treatments,the surface roughness of heavy load wheel steel dropped to below 4?m.The surface hardness has certain increase,and induce useful surface residual compressive stress.Deformation layer of certain thickness was formed on the surface.Meanwhile,the surface grains broken into equiaxed nanocrystalline.Through different surface treatment process,the heavy load wheel steel could meet the operating requirements of different service condition.From the surface hardness result of the pure iron and CL65 treated by ultrasonic impact with one time,two times and three times,we conclude that the improvement of wheel surface hardenss is due to work hardening,fine grain strengthening and solution strengthening.We generate ultrasonic impact for 3 times on the materials with different carbon content under the conditions of 120w power,450r/min rotate speed and 0.05mm/r feeding speed.And from the comparison,we conclude that the deformation layer in pure iron has the deepest depth and the surface hardness largely increases to 80%.And with the worst hardening effect of the rail steel,so we conclude the hardening process of the wheel and rail under the ultrasonic impact.First,the ferritic phase undergo the plastic deformation,and with the increase of deformation degree,the stress concentration formed around the pearlitic cementite,so that the cementite begin to refine,distort and fracture,meanwhile some of the cementite has dissolved,at last the surface hardness of material increased remarkably.