Refinement effect of NbC particle additions on the microstructure of high-speed steel rolls

High-speed steel (HSS) rolls modified by different additions of NbC were prepared. The microstructure of as-cast and heat-treated NbC-modified HSS rolls were observed by means of optical microscope (OM), scanning electron microscope (SEM) and energy spectroscopy (EDS), combining with the result of dissolution behavior of NbC particles and interface energy of NbC/γ-Fe calculated by dissolution kinetic and first-principle, the effect of addition of NbC on microstructure of HSS rolls were discussed. Results show that NbC particles do not dissolve in melt under experimental conditions, and the NbC particles even coarsen due to the absorption of alloying elements during the subsequent cooling process. The NbC particles can act as the heterogeneous nucleuses of pre-eutectic austenite to refine the as-cast microstructure of HSS rolls. However, the added amount of NbC particles influence the distribution of NbC. With the increase of the amount of NbC particles, the distribution of NbC particles changes from austenite inter-dendrite region to dendrite. The NbC particles distributed in austenite inter-dendrite region can restrain the movement of solid-liquid interface, and refine the as-cast microstructure. The distribution of NbC within the austenite dendrites enhances the potential of NbC as a non-homogeneous phase nucleus, thereby further refining the microstructure.