Study On The Wear Properties Of U71MnK And U71MnG Rail Weld During Rolling Contact

Because of the higher performance-price ratio than others, U71MnK,U71MnG rails are generally adopted in the common rail lines and the seamless rail lines. The high voltage resistance welding is adopted widely, but many problems haven’t solved. The weld is inclined to show some unlike characteristic when it is compared with the non-weld, such as "hogback", severe wear and high plastic deformation and so on. In addition, because of weld, the vertical acceleration of the vehicle axle box increases, so the vehicle vibration aggravate and this influences the ride comfort. At present, the research on the abrasion performance of the rolling contact is less. In view of this, the material wear evolved behaviors of the two kinds of rail weld and base material in the process of rolling contact were investigated through the simulated experiments by adopting the method of analysis. The MMS-2A friction wear testing machine controlled by microprocessor, SEM, OM, and so on are used.The main conclusions are drawn as folliows:1.There are significant differences between the weld and the non-weld before and after wear. Compared with the base material, the weld zone is a oxydic decarburization layer where there is lean carbon. The grains are coarse and uneven. Because of the carbonation in the welding process, the percentage of pearlite and ferrite decreases, and its mechanical properties, such as toughness and plasticity are changed. Due to the differences in microstructure and mechanical properties, the hardness of the weld zone is lower than that of the non-weld zone. The friction coefficient, wear volume and wear rate of the weld zone are greater than that of the non-weld zone. Compared with the non-weld zone, the furrows and corrugations are prone to generate in the weld zone. Moreover, surface roughness increases. Spalling damage, cracks, plastic deformation aggravate and abrasion performance deteriorates in the weld zone. The previous microstructure both in the weld zone and the non-weld zone is refined by the previous wearing, which results in the wear resistance improving. Thus, the abrasion damage reduces in the subsequent rolling contact.2.The microstructure of U71MnG is slightly different compared with that of U71MnK. Whether the weld or the base material, their structure is different. The grains of U71MnG are more reticular than that of U71MnK. The angle difference between adjacent grains is bigger. Differential difference performance is better. The toughness and hardness are higher. Therefore, the functional performance of U71MnG is better than that of U71MnK under high speed, and there is less wear, milder plastic deformation, subtler crack in the three corresponding area. The friction coefficient is almostly the same in the three corresponding area, and the grinding spot are no differences from different areas. After improving the speed, the functional performance gets better.3.For U71MnG, the wheel/rail rolling friction coefficient gets smaller under higer speed, but the coefficient get bigger under less speed. The higher the speed is, the lighter the degree of the sample surface wear, and the rail corrugation are. The wear volume decreases slighter under high speed. The other characteristics such as hardness changes, rai temperature, metallographic structure, deformation, crack and so on are almost the same.4.There is no different temperature change and they are all in low temperature.