Research On Mechanical Properties Of ER8 High Speed Wheel Steel At Low Temperature And Pre-corrosion State

The localization of high-speed railway wheels has been put on the agenda in recent years.To develop EMU wheels with China’s independent intellectual property rights,we must first do further study on wheel materials.At present,we have made great progress in the study of wheel materials,but the study of its serving in special circumstances,such as low temperature,pre-corrosion,etc,has not yet caused extensive attention of the researchers.In low temperature or pre-corrosion environment,the fatigue behavior and damage mechanism of wheel materials are not clear.Consequently,the data accumulation of basic mechanical performances and further study of fatigue performance of wheel materials in special service environment are of great significance,providing theoretical foundation for the research,maintenance,repair and scrapping of high-speed railway wheels.In this paper,the mechanical performances in low temperature and the friction and wear properties and fatigue properties in pre-corrosion environment of ER8high-speed wheel steel are studied.We analyses the fracture morphology and wear morphology by using scanning electron microscope（SEM）and super-depth microscope.We pay more attention on how low temperature and pre-corrosion influence the fatigue damage mechanism.The main conclusions are as follows:（1）The strength of wheel steel increases with decreasing temperature.In the test temperature range-40℃≤T≤25℃（room temperature）,the change of tensile strength is almost linear relationship.The plasticity decreases with decreasing temperature.With decreasing temperature,the impact energy value gradually decreases,the impact performance of rim materials is obviously better than that of the wheel web,and the low temperature environment shortens the plastic cracking process.In the surface grinding zone of rims,the hardness gradient is linearly reduced,and the hardness value of the wheel is almost unchanged with 215HB after 150mm from the tread surface.（2）The fatigue limit is almost same with the above two methods.The data volume is smaller,the dispersion degree is greater.When stress ratio R=0.1,the fatigue limit of materials in low temperature increases significantly,which increases from585MPa at room temperature to 654MPa and increases by about 70MPa.The fatigue crack initiates at the surface of the sample and all of them are single crack.（3）The corrosion layers of rim materials are divided into two layers.The outer layer is loose yellow-brown Fe（OH）₃ andγ-Fe OOH.The inner layer is blackα-FeOOH and Fe₃O₄.With increasing corrosion time,the average corrosion velocity first reduces,then increases and last decreases.The maximum lost weight after corrosion of 72h is approximately 43.374mg/cm².（4）With increasing pre-corrosion time,the sample surface spalling behavior significantly intensifies.Peeling area is increasing rapidly and the weight loss is greater.After wearing for 65 minutes without corrosion,the weight loss is about 36.61mg.After pre-corrosion for 72h,the weight loss increases by 40%.With increasing corrosion time,the average friction coefficient gradually increases.The average friction coefficient reaches the maximum after pre-corrosion for 48h.With increasing pre-corrosion time continuously,the friction coefficient gradually decreases.（5）With the increase of pre-corrosion time,the fatigue limit drops sharply.The fatigue limit of pre-corrosion for 6h is 547MPa,and the fatigue limit of pre-corrosion for 48h is 430MPa,which decreases rapidly compared with room temperature（585MPa）.Fatigue on the surface of the specimen starts to crack at multiple locations.