Effect of Upper Bainite on Wear Behaviour of High-Speed Wheel Steel

This paper presents the wear and damage behaviours of the wheel/rail material of ER8 and of U71Mn under the same cycles condition, which were explored using a double-disc rolling wear testing device. The morphology of the worn surface and the morphology of cross sections were observed by laser scanning confocal microscopy (LSCM) and scanning electron microscopy (SEM). Results show that the microstructure of wheel steel includes ferrite, pearlite and upper bainite. As the cycles increased, the weight loss of the wheel steel containing upper bainite is significantly increased when compared with ferrite–pearlite wheel steel, and the plastic layer is more deformed than the ferrite–pearlite wheel steel. The deformation of the upper bainite is easier than the pearlite, and the cementite in the upper bainite presents granularity and short rod-shaped. With only ferrite and pearlite in the microstructure, the main wear mechanism varies from oxidative wear to adhesive wear and eventually into fatigue wear. When the microstructure is composed of ferrite, pearlite and upper bainite, the main wear mechanism changes from oxidative wear to ploughing wear and abrasive wear, and ultimately to fatigue wear.