This study systematically investigated the distribution characteristics of inclusions and precipitates across the entire thickness, at 1/4 width position of the 450 mm thick and 1870 mm wide calcium‐treated steel ultra‐thick slab. The four most abundant inclusions are TiN, MgO+Al 2 O 3 +CaO+CaS, Al 2 O 3 +CaO+CaS, and CaS, accounting for 25.53%, 13.75%, 12.63%, and 9.26% of the total number, with the average diameters of 4.03, 6.46, 6.60 and 5.46 μm, respectively. Al 2 O 3 inclusions aggregate at the 1/4 thickness position of the slab due to the floatation of large clustered Al 2 O 3 inclusions in molten steel. The CaS inclusions larger than 5 μm aggregate near the 1/4 to 3/8 thickness of the slab, indicating that larger CaS particles are more likely to float up to these positions to be captured. The (Al 2 O 3 +CaO) containing inclusions tend to aggregate at the center of the slab thickness near the end of columnar crystal zone of the loose side due to the slower flotation speed of those inclusions. TiN number density is higher internally and lower at slab edges because the fast cooling induces fine TiN precipitation. MnS accumulates at the thickness center due to Mn and S segregation during solidification.
Sun et al. (Thu,) studied this question.