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Oxidation behavior of rails during grinding process
2024-12-25
During the interaction between abrasives and rails, the plastic deformation of the rails generates heat, and the friction between abrasives and rail materials also generates grinding heat. The grinding of steel rails is carried out in a natural atmosphere, and during the grinding process, the steel rail material is inevitably oxidized under the heat of grinding. There is a close relationship between surface oxidation of steel rails and rail burns. Therefore, it is necessary to study the oxidation behavior of the rail surface during the grinding process.
It has been reported that three types of grinding stones with compressive strengths were prepared, with strengths of 68.90 MPa, 95.2 MPa, and 122.7 MPa, respectively. According to the order of grinding stone strength, GS-10, GS-12.5, and GS-15 are used to represent these three groups of grinding stones. For the steel rail samples ground by three sets of grinding stones GS-10, GS-12.5, and GS-15, they are respectively represented by RGS-10, RGS-12.5, and RGS-15. Conduct grinding tests under grinding conditions of 700 N, 600 rpm, and 30 seconds. In order to obtain more intuitive experimental results, the rail grinding stone adopts a pin disc contact mode. Analyze the oxidation behavior of the rail surface after grinding.
The surface morphology of the ground steel rail was observed and analyzed using SM and SEM, as shown in Fig.1. The SM results of the ground rail surface show that as the grinding stone strength increases, the color of the ground rail surface changes from blue and yellow brown to the original color of the rail. The study by Lin et al. showed that when the grinding temperature is below 471 ℃, the surface of the rail appears normal color. When the grinding temperature is between 471-600 ℃, the rail shows light yellow burns, while when the grinding temperature is between 600-735 ℃, the surface of the rail shows blue burns. Therefore, based on the color change of the ground rail surface, it can be inferred that as the strength of the grinding stone decreases, the grinding temperature gradually increases and the degree of rail burn increases. EDS was used to analyze the elemental composition of the ground steel rail surface and debris bottom surface. The results showed that with the increase of grinding stone strength, the content of O element on the surface of the rail decreased, indicating a reduction in the binding of Fe and O on the surface of the rail, and a decrease in the degree of oxidation of the rail, consistent with the trend of color change on the surface of the rail. At the same time, the content of O element on the lower surface of the grinding debris also decreases with the increase of grinding stone strength. It is worth noting that for the surface of the steel rail ground by the same grinding stone and the bottom surface of the grinding debris, the content of O element on the surface of the latter is higher than that of the former. During the formation of debris, plastic deformation occurs and heat is generated due to the compression of abrasives; During the process of debris outflow, the bottom surface of the debris rubs against the front end surface of the abrasive and generates heat. Therefore, the combined effect of debris deformation and frictional heat leads to a higher degree of oxidation on the bottom surface of the debris, resulting in a higher content of O element.
(a) Low strength grinding stone ground steel rail surface (RGS-10)
(b) Surface of steel rail ground with medium strength grinding stone (RGS-12.5)
(c) High strength grinding stone ground steel rail surface (RGS-15)
Fig. 1. Surface morphology, debris morphology, and EDS analysis of steel rails after grinding with different intensities of grinding stones
In order to further investigate the oxidation products on the surface of steel rails and the variation of oxidation products with the degree of rail surface burn, X-ray photoelectron spectroscopy (XPS) was used to detect the chemical state of elements in the near surface layer of ground steel rails. The results are shown in Fig.2. The full spectrum analysis results of the rail surface after grinding with different intensities of grinding stones (Fig.2 (a)) show that there are C1s, O1s, and Fe2p peaks on the ground rail surface, and the percentage of O atoms decreases with the degree of burn on the rail surface, which is consistent with the pattern of EDS analysis results on the rail surface. Due to the fact that XPS detects the elemental states near the surface layer (about 5 nm) of the material, there are certain differences in the types and contents of elements detected by XPS full spectrum compared to the steel rail substrate. The C1s peak (284.6 eV) is mainly used to calibrate the binding energies of other elements. The main oxidation product on the surface of steel rails is Fe oxide, so the narrow spectrum of Fe2p is analyzed in detail. Fig.2 (b) to (d) show the narrow spectrum analysis of Fe2p on the surface of steel rails RGS-10, RGS-12.5, and RGS-15, respectively. The results indicate that there are two binding energy peaks at 710.1 eV and 712.4 eV, attributed to Fe2p3/2; There are binding energy peaks of Fe2p1/2 at 723.7 eV and 726.1 eV. The satellite peak of Fe2p3/2 is at 718.2 eV. The two peaks at 710.1 eV and 723.7 eV may be attributed to the binding energy of Fe-O in Fe2O3, while the peaks at 712.4 eV and 726.1 eV may be attributed to the binding energy of Fe-O in FeO. The results indicate that Fe3O4 Fe2O3. Meanwhile, no analytical peak was detected at 706.8 eV, indicating the absence of elemental Fe on the ground rail surface.
(a) Full spectrum analysis
(b) RGS-10 (blue)
(c) RGS-12.5 (light yellow)
(d) RGS-15 (original color of steel rail)
Fig.2. XPS analysis of rail surfaces with different degrees of burns
The peak area percentages in the Fe2p narrow spectrum show that from RGS-10, RGS-12.5 to RGS-15, the peak area percentages of Fe2+2p3/2 and Fe2+2p1/2 increase, while the peak area percentages of Fe3+2p3/2 and Fe3+2p1/2 decrease. This indicates that as the degree of surface burn on the rail decreases, the Fe2+ content in the surface oxidation products increases, while the Fe3+content decreases. The different components of the oxidation products result in different colors of the ground rail. The higher the degree of surface burn (blue), the higher the content of Fe2O3 products in the oxide; The lower the degree of surface burn, the higher the content of FeO products.