Origin of Austenitization-Dependent Eutectoid Transformation in High-Speed Steel: Revisiting the Role of Primary Carbide

Tuning eutectoid carbides through tailoring austenitization parameters offers an alternative pathway for the ductility enhancement of high-speed steels. This study probes the origin of austenitization-dependent eutectoid reaction and revisits the role of primary carbides in the annealing process. The increase of austenitization temperature and/or duration produces more rod-shaped eutectoid carbides while suppressing their granular counterparts, corresponding to a transition of eutectoid transformation from a divorced mode to a lamellar manner. Primary carbides can serve as chemical conditioners of the austenite as well as nucleation substrates of eutectoid carbides. Austenitization conditions determine the dissolution of primary carbides and concurrently affect the two essential factors of eutectoid reaction modes, i.e., the inter-particle spacing and the undercooling, thereby causing the austenitization dependence of eutectoid carbides in high-speed steels.