Comparison of Chinese and foreign manufactured steel rails for Chinese railways over a century: chemical compositions, microstructure and hardness

The changes in chemical composition, microstructure and hardness of the steel rails for Chinese railways over a century are investigated to compare the development of the steel rails manufactured by China and fremdness. More importantly, the microstructural evolutions are discussed in detail through advanced characterizations of OM, SEM and EBSD. The results show that the carbon content increases with time passing, and the elements of phosphorus and sulphur are properly controlled. Besides, the Chinese steel rails have an increase tendency in the manganese content, on the contrary, a decrease trend exists for the foreign steel rails. The OM and SEM images reveal that the microstructure varies from ferrite with a few of pearlite to pearlite with reticulated ferrite to full pearlite. From the results obtained by EBSD analyses, it is found that the average grain diameter of pearlite cluster in the steel rails decreases with scientific and technological progress. Moreover, it exhibits lower grain boundary misorientation in the steel rails produced after 1950s leading to avoid local stress concentration during plastic deformation and thus weaken crack nucleation. Furthermore, the hardness of the Chinese steel rails is lower than that of the foreign steel rails.