Effect of Contact Stress on the Evolution and Properties of FCB Wheel Steel

The rolling wear test of bainitic wheel steel was carried out using a double-disc rolling friction and wear tester, and the microstructure evolution of the sub-surface layer of bainitic wheel steel under different contact stress conditions was analyzed by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The results showed that under the conditions of rolling wear, the wear mechanism transited from adhesive wear to fatigue wear. Increasing contact stress had little effect on the amount of wear in the adhesive wear stage, while it significantly increased the amount of wear in the fatigue wear stage of bainitic wheel steel. In the process of plastic deformation, the dislocations in the bainitic ferrite lath gradually increased and firstly accumulated to form small-angle grain boundaries, and then formed large-angle grain boundaries. Consequently, bainitic ferrite was refined; the magnitude of contact stress affected the evolution of the surface structure. When the contact stress increased to 1 150 MPa, the grains were refined into ultra-fine equiaxed crystals. As the contact stress further increased, and the structure change was not obvious. The contact stress affected the surface hardness of the bainitic wheel steel. The increase in contact stress increased the surface hardness of the bainitic wheel steel and the depth of the hardened layer increased.