Full-scale spark mapping of elements and inclusions of a high-speed train axle billet

Railway axles are important components of high-speed trains. A study of the uniformity of chemical composition and the distribution of non-metallic inclusions and carbides in high-speed railway axles is required to ensure safety during service. Until now, no instrument has been available for full-surface analysis of the composition and inclusion of high-speed railway axles which are nearly two meters in length. In this work, a Spark Mapping Analysis for Large Samples (SMALS) technique was designed and developed for the first time. Based on the spectral intensity signal obtained via spark emission spectrometry and mega data model calculation, it was utilized for the characterization of the full surface of a large metal sample of size up to a meter. The chemical composition, and non-metallic inclusion and carbide distribution in a high-speed railway axle billet were obtained by this method. The segregation belt was characterized in the transverse and longitudinal sections. Elements such as Mn, V, and Mo were inclined to segregate at similar to 1/4 part from the billet edge, and S and Al were segregated in the central region. The carbide amount in the center was higher than at the edge. Alumina existed as the main inclusion and was distributed in the center of the cross-section and longitudinal section. MnS inclusions are also distributed in the center. The comparison of micro-beam X-ray fluorescence results confirmed the accuracy of the SMALS technology in determining the chemical composition distribution and segregation belt. For elements with low contents such as Cu or light elements such as Al, SMALS showed an obvious advantage in the sensitivity of surface characterization. The comparison of the hardness test with the carbon distribution of SMALS showed satisfactory consistency. Thus the SMALS technique is conducive to the optimization of the production process.