Acceleration of Spheroidization in Low‐Density Ultrafine Pearlitic Steel by κ‐Carbide

The impact of κ‐carbide on the spheroidization process of low‐density ultrafine pearlitic steel (with 5 wt% Al and 5 wt% Mn additions) is investigated through isothermal annealing spheroidization. In the findings, it is demonstrated that κ‐carbides can significantly refine the lamellar spacing of low‐density ultrafine pearlite during the isothermal transformation. Additionally, under identical conditions, κ‐pearlite exhibits a higher number of ferrite/κ‐carbide interfaces. In the first stage of pearlite spheroidization, an abundance of dislocations and sub‐grain boundaries facilitate rapid fusion of the lamellar pearlite, while in the second stage, they provide a high‐speed diffusion pathway for carbon diffusion. Moreover, the reduced lamellar spacing shortens the distance for carbon and alloying elements diffusion, thereby promoting granular κ‐carbide formation and accelerating spheroidization in low‐density ultra‐fine pearlite.