New insight into the dry rolling-sliding wear mechanism of carbide-free bainitic and pearlitic steel

The comparison of wear resistance of bainitic and pearlitic steel is still a matter of controversy. In this study, the dry rolling-sliding wear behaviors of three types of pearlitic steel and one carbide-free bainitic rail steel have been investigated. Although the carbide-free bainitic U22SiMn demonstrated the highest initial hardness, it presented heavier wear loss than the other two kinds of pearlitic rail-steel. On the other hand, the U22SiMn induced lightest wear loss to its coupled CL60 wheel steel. Our analysis reveals two factors behinds the experiment results. First, the strain hardening ability of carbide-free bainitic U22SiMn was inferior to the pearlitic microstructure. Meanwhile, the distribution of micro-hardness suggested that the steep hardness gradient of the area adjacent to the contact surface played the same role of high strain hardening exponent on improving wear resistance of materials. Both of these two measurable parameters can be used to assess the wear resistance of materials. Second, the white etching layer (WEL) could only be discovered on the worn surfaces of pearlitic steel, but was absent in bainitic U22SiMn. The existence of hard WEL on the worn surface could contribute to improvement of the wear resistance. Our experiment observations and theoretical analyses provide an in-depth understanding of the wear resistance, which can be enhanced by achieving an optimal combination of the strain hardening exponent (or yield-tensile ratio) and the initial hardness. Particularly, this understanding can benefit the development of new rail/wheel steel with excellent wear resistance.