Tinghui Man

The flow stress curves of Fe‐31.7Mn‐11.5Al‐0.9C low‐density steel are obtained by a hot‐compression test with a Gleeble‐3500 thermomechanical simulator. It is shown in the results that the dynamic recovery and dynamic recrystallization (DRX) of δ‐ferrite occur preferentially under the same deformation condition, inducing a “yield point‐like” phenomenon in the true stress–strain curves. The Zener–Hollomon parameter is introduced to fit the characteristic parameters used to establish the flow stress model according to Arrhenius hyperbolic sine relationship and Avrami equation, and the DRX activation energy of austenite is 414.12 KJ mol⁻¹. The hot‐processing maps at different true strains are simulated based on the dynamic material model to determine the suitable hot‐rolling process and the optimal hot‐working process selection of high strain rate and high deformation temperature combination, 1100–950 °C/1–0.2 s⁻¹, is recommended.

The microstructural evolution of the rail steels manufactured by Hanyang Iron Works was investigated through optical microscopy (OM), scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). The OM and SEM images reveal that the microstructures are ferrite with a small amount of pearlite in the rail steel 1904, reticular ferrite and pearlite in the rail steels 1911 and 1921, and full pearlite in the rail steels 1917 and 1919, respectively. The EBSD results show that the rail steel 1904 holds the smallest average grain diameter owing to the pearlite with small size. Moreover, the average grain diameter of the pearlite cluster decreases in the rail steels manufactured after 1908, except for 1921, when it was on the verge of bankruptcy. The rail steels 1917 and 1919 exhibit a higher proportion of low angle grain boundaries and local misorientation with angles lower than 1°. Besides, the grain boundary misorientation holds a lower proportion in the range of 40~50° in the rail steels 1917 and 1919.