Effects of Cooling Rate and Ni on Precipitation Law of Ceramic Particles in Cast Fe-TiB₂ Steel

The Fe-TiB₂ particle-reinforced steel was prepared by vacuum arc melting process. The effects of sub-rapid cooling rate and Ni on the precipitation regularity of TiB₂ particles were studied. The results show that the casting microstructure of Fe-TiB₂ steel consists of two phases of α-Fe and TiB₂. Under sub-rapid cooling casting conditions, the TiB₂ phase cannot be completely precipitated. The primary TiB₂ ceramic phase is coarse block-like particles with sharp corners, and the eutectic TiB₂ ceramic phase is fine and irregular strip-like morphology. The volume fraction of primary TiB₂ ceramic phase decreases with the decrease of cooling rate, while the volume fraction of eutectic TiB₂ ceramic phase increases. During the casting process of Fe-Ti-B ternary steel, there is a pro-eutectic transformation process of δ-Fe ferrite and TiB₂ primary phase.Ni in Fe-Ni-Ti-B quaternary steel inhibits the high temperature precipitation of primary TiB₂ phase and δ-Fe ferrite, and promotes the eutectic transformation of γ-Fe and TiB₂ , thus significantly changing the room temperature casting microstructure composition and distribution characteristics of the reinforcing phase TiB₂ ceramic particles.