Research Of Wheel Tread Damage And Its Laser Cladding Reparation In High-speed Train

With the number of EMUs rising year by year, the problem of wheels injury is becoming increasingly prominent,especially wheel tread. The wheels damage mechanism and wear resistance of high-speed train have become focused issues and trends in research. We can do laser cladding experiment on wheels material to improve friction wear properties, which has very important economic value and practical significance to the development of high-speed railways.In present paper,wear tracking experiment on CRH1 on a existing railway line and collecting damaged rail specimen samples are done and then the damage mechanism of high speed train wheels is studied; laser cladding experiments are carried out on high-speed trains ER8 wheel steel material surface with diode solid-state laser, and microstructure, phase and microhardness are analyzed, then wear properties of cladding layer is studied through the simulation of wheel/rail movement on wear and abrasion test machine, and finally optimum overall performance of laser cladding process parameters is obtained through positive post test analysis. The main conclusions of the study are as follows:(1)It is found that tread wear increases with the increase of operating mileage of the EMU with wheel tread wear track test, and the wear increases dramaticly after 261 thousand km. Wheel-rail contact geometric relationship under different operating mileage is simulated by SIMPACK, it’s known that there are three phases on wheel tread wear, and the wear become violent and easy to produce contact fatigue after 232 thousand km.(2)There are three main sources of wheel tread damage: circular wear, rolling contact fatigue and braking. Tread profile will change after circular wear, thus change the geometry of the wheel-rail contact relationship, further affect vehicle dynamics performance; rolling contact fatigue damage will result in fatigue cracking and tread peeling; brake will bring hot strip and hot cracking, and flat sliding will generate if braking force is too strong. These three types of damage sources influence each other, and you may see morphology of brake stripping failure and contact fatigue failure on the same failed wheel.(3)Fe-based cladding layer metallurgically combines with ER8 substrate can be obtained through the laser cladding process, and the cladding layer mainly comprises γ-Fe phase as matrix phase and the hard phases like carbide Cr7C3 and compounds with Mn, Mo, Ni and other alloying elements, in the cladding layer substitutional solid solution will be formed by those hard phase and γ-Fe,which greatly increases the strength of the cladding layer. The cladding structure is divided into planar crystal area, columnar dendrites area, cellular crystal area and equiaxial dendrites area from the inside out district, and the fomation of there structures is dicided by the temperature gradient and rate of solidification ratio(G / R).(4)The impacts of different laser power, laser scanning speed and feed rate on microstructure and mechanical properties of cladding layer was studied. The result show that hardness and wear resistance first increase and then decrease with the increase of these three parameters, and the scanning speed is the ultimate affection of cladding performance, the powder feed rate is the week influence, and the laser power between the former affection factor.(5)Orthogonal experiment is designed and each group spcimen is tested on wear and abrasion test machine with rail material for the grinding material, finally the optimized laser processing parameters are obtained: the laser power P=1.6kW, scanning speed vs=400mm/min and the feed rate vf =20g/min, in which the cladding layer hardness increased 1.42 times, relative wear resistance increased 2.1times, and the weight loss of wheel-rail friction pair is least.