Effects of Rare-earth and Microalloying Elements on the Microstructure Characteristics of Hypereutectoid Rails

We performed thermal simulation experiments of double-pass deformation of hypereutectoid rails with different microalloying elements at a cooling rate of 1°C/s and deformation of 80% to explore the influence of rare-earth and microalloying elements on the structure of hypereutectoid rails and optimize the composition design of hypereutectoid rails. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and other characterization techniques were employed to quantitatively analyzed the effects of different microalloying elements, including rare-earth elements, on pearlite lamellar spacing, cementite characteristics, and dislocation density. It was found that the lamellar spacing was reduced by adding various microalloying elements. Cementite lamellar thickness decreased with the refinement of pearlite lamellar spacing while the cementite content per unit volume increased. Local cementite spheroidization, dispersed in the ferrite matrix in granular form and thus playing the role of dispersion strengthening, was observed upon adding cerium (Ce). The contributions of dislocation density to the alloy strength of four steel sheet samples with and without the addition of nickel, Ce, and Ce–copper (Cu) composite were 26, 27, 32, and 37 MPa, respectively, indicating that the Ce-Cu composite had the highest dislocation strengthening effect. The Ce−Cu composite has played a meaningful role in the cementite characteristics and dislocation strengthening, which provides a theoretical basis for optimizing the composition design of hypereutectoid rails in actual production conditions.