In situ X-ray analytical study on the alteration process of iron oxide layers at the railhead surface while under railway traffic

This paper describes an experimental investigation of in situ X-ray diffraction analysis of iron oxides on the railhead surface, which have an influence on various wheel/rail rolling contact phenomena, e.g. the adhesion between wheels and rails, which can cause rail corrugations. The X-ray analysis using portable X-ray diffractometer installing XRF called “XRDF” was carried out for the preliminary laboratory experiment and the field test. For the laboratory experiment, the rail specimen samples on which rust was generated by scattering salt water mist and moisture vapor alternately were analyzed. The different rust types generated under the different environmental conditions were identified. For the field test, XRDF analysis was applied to the corroded test rail after the test vehicle passed over it several times. As a result, it can be concluded that the decreased proportion of rusts due to passage of the vehicle depends on the track alignment, the location where rails are installed, and the positions across the rail head such as top of rail in tangent track or gauge corner of the high rail in curved track, and also depends on the vehicle running conditions, i.e. free-rolling, driving or braking. Finally, we confirmed the effectiveness of applying XRDF analysis to track site measurements to obtain some important suggestions for understanding the wheel/rail rolling contact phenomena on which rail surface substances have great influence.

Research highlights▶ Several types of iron rusts generated on the railhead surface at the actual track were identified by applying X-rays to in situ analysis. ▶ The rusts at the gauge corner of the high rail in curved track are more quickly removed by the railway vehicles than those generated at top of the rail in tangent track. ▶ The rusts are easier to be removed by the railway vehicles under driving and/or braking operation than under free-rolling.