Study On Surface Strengthening Of Rail Transit Materials By Ultrasonic Impact Treatment

In recent years,because of high speed and heavy load, the fatigue life of the axle reduces,wheel and rail wear increases,the frequency of replacing turnout increases, which poses a severe challenge to road safety.UIT is a method to make metal material surface produce plastic deformation,ultimately significantly improve the surface properties,and has been used in the surface hardening of stainless steel、mild steel welding and titanium alloys. UIT has deeper hardening layer、faster processing speed, small size、light quality、less noise pollution、low cost and energy-saving、not limiting the workpiece shape and also composes production lines with other equipment components etc.,so we may be put the technology of UIT into the surface strengthening of rail transit materials,to improve the mechanical properties of the material.The test results showed that the rail surface produces severe plastic deformation as the wheel rolls repeatedly,which significantly improves surface hardness. After the ultrasonic impact treatment, the surface of the sample produces plastic deformation,grain size decreases;With increasing depth from the surface, the deformation quantity decreases,successively divided into severe deformed layer、 transition layer and the matrix. The microhardness presents gradient change.With increasing depth from the surface, the hardness decreases until the hardness reaches stabilized value. With the increase of ultrasonic impact power, speed and the numbers, the thickness of surface deformation layer increases, the surface hardness increases; With the increasing power of the sample,surface roughness is reduced, and the maximum is about nine times; When rail steel is under the action:180w,1170r/min,9times,the deformed layer thickness is230μm, the maximum hardness is860HV, which increases nearly1.5times. On the surface of the axle steel observes nanocrystalline and grain size is40-50nm. Under the same process parameters, both surface hardness and hardening rate of the rail steel are max. Hardness increase is attributed to the result of sample cold hardening and grain refining.Considering various factors, determining the optimum parameters of UIT as:180w、820r/min、 three times.