Fracture toughness of nanostructured railway wheels

This paper describes nanostructured railway wheels made of Si–Mn–Mo–V low-carbon steel through an advanced metallurgy process and fabrication technology. The microstructure of the wheels, particularly in the rim portion, is composed of carbide-free bainite that consists of bainitic ferrite laths and retained austenite films along the lath boundaries. The thickness of the laths and films is in nanometer scale. For comparison, traditional pearlite–ferrite wheel steels are also investigated. Test results show that carbide-free bainite steel is superior to pearlite–ferrite steel not only in yield strength but also in fracture toughness. Theoretical explanation of these phenomena is also elucidated.