Sliding Friction and Wear Behavior of Flash-Welded U75V Steel Joints in Air and Water Environments

Abstract

U75V high-strength steel has been widely used to improve the service life of high-speed rails. Considering the consecutive cold and wet condition of the Sichuan–Tibet highway, water plays an important role in the wear process of U75V welded joints. In this study, we investigated the wear behaviors of flash-butt-welded U75V joints in dry air and water environments using a ball-on-disk sliding wear tester. The worn surfaces were tested using optical microscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The cross-sectional profiles of the wear scar were tested using a wear volume tester. The results show that the U75V welded joint has a lower wear resistance than the base metal owing to its nonuniform structure and exhibits a high friction coefficient (0.64) and wear loss (0.21 mm3) in dry air. Water exerts a lubricating function on the fretting wear of U75V welded joints and reduces the friction coefficient (0.36) and wear loss (0.15 mm3). Furthermore, abrasive wear and micropitting are predominant in water environment, accompanied by the formation of a protective-oxide layer on the surface. In contrast, microcutting and microcracking are the dominant wear mechanisms of U75V welded joints in dry air.