Distribution of Bi-MnS inclusions in newly solidified steels subjected to horizontal cooling.

To further study the distribution and concentration of Bi particles in various cooling zones in newly solidified Bi content 1215 MS steels and to explore the relationship between cooling rate (R) and dendrite arm spacing, the horizontal solidification experiments were carried out by altering the R. Thermodynamics show liquid Bi was immiscible in Fe, which precipitated in the grain boundary and tended to co-exist with sulfides. Under moving rate ν = 0.2 mm/s, the average sizes of Bi particles and Bi-MnS inclusions in the chilled boundary, columnar grain and quenching grain zones were 1.2 μm, 1.4 μm, and 1.5 μm, while under v = 0.4 mm/s, those were 1.3 μm, 1.6 μm, and 1.2 μm, respectively. The average dendrite arm spacing of the solidified steel decreased with increasing moving rate (v). At R = 0.367 and 0.690°C/s, the average equivalent diameter ( d ˉ e ) of the inclusions in the columnar grain zone was respectively 1.102 μm and 1.119 μm. Under v = 0.4 mm/s, the concentrations of Bi particles in 1200 ppm and 2800 ppm Bi solidified steels in the chilled boundary, solidification front and center of the quenching grain zone were 0.0267%, 0.0375%, 0.0443%, 0.0463%, 0.0659%, and 0.0832%, respectively. [ABSTRACT FROM AUTHOR]