Effect of Electromagnetic Stirring on Inclusions in Continuous Casting Blooms of a Gear Steel

The effect of electromagnetic stirring at a continuous casting strand on the distribution of inclusions along the thickness of gear steel blooms was investigated. Inclusions in the subsurface of continuous casting blooms were Al2O3·CaO·CaS·MgO, similar to those in the molten steel of continuous casting tundish. Inclusions at 1/4 thickness from the loose side and the center of the bloom were Al2O3·CaS·MgO. The spatial distribution in the number density and composition of inclusions along the thickness from the loose side to the fixed side of the bloom was non-uniform but symmetric. The electromagnetic stirring efficiently improved steel cleanliness by lowering the average number density and area fraction of inclusions in the whole section of the CC bloom from 58.14 #/mm2 and 176.82 ppm to 30.90 #/mm2 and 111.67 ppm, respectively, and by increasing the average size and the maximum size of inclusions from 2.73 and 20.84 μm to 2.99 and 76.02 μm, respectively. More large-size inclusions contained K and Na by the slag entrainment in the mold with electromagnetic stirring were detected than those without electromagnetic stirring. Seven mm of the bloom from the loose side was analyzed for inclusions with size > 1.0 μm every 1 mm depth. The average CaO content of inclusions with size > 1.0 μm within the 7 mm subsurface of the bloom increased from 5.67 wt pct without electromagnetic stirring to 16.12 wt pct with electromagnetic stirring and increased from 10.24 wt pct without electromagnetic stirring to 21.31 wt pct with electromagnetic stirring for > 3.0 μm inclusions, which confirmed that unreasonable current electromagnetic stirring operation parameters will lead to slag entrainment.