In order to explore the change mechanism of friction coefficient of wheels in different environments,the friction and wear properties of ER8 wheel steel in dry air,pure water and 3.5% sodium chloride solution were investigated by sliding friction testing machine.The wear scars and elemental composition were analyzed by optical microscope,scanning electron microscope,non-contact three-dimensional surface profilometer and X-ray diffractometer,and the friction and wear mechanism of ER8 wheel steel in different environments was discussed.The results show that the friction coefficient of ER8 wheel steel increases obviously with the increase of load.The service environment of train has great influence on the friction and wear performance of wheel.In dry air,ER8 wheel steel has no corrosion,the wear scar width is the smallest,but the friction coefficient is the largest,up to 0.503.In salt water environment,the corrosion phenomenon of ER8 wheel steel occurs,the wear scar width is the largest,but the friction coefficient is the smallest.The wear mechanisms of ER8 wheel steel under dry friction are adhesive wear,abrasive wear and oxidative wear,while the wear mechanisms under the environments of pure water and 3.5%NaCl solution are abrasive wear and oxidative wear.