To understand the sintering behavior of zircon-based filler sands, laboratory experiments are conducted, and the effect of steel grades containing different contents of Mn and Al is studied. The results show that zircon filler sands have a sufficient sintering performance without the influence of steel. The reaction between the mullite grains and the decomposed zircon grains results in the formation of a liquid phase, making the sand grains bond. Liquid steel (even liquid pure iron) evidently impacts the sintering of zircon filler sands. Similar to chromite filler sands, the effect of Mn in liquid steel on the sintering of zircon filler sands is also remarkable, whereas the effect of Al (up to 250 ppm) is not so profound due to the existence of the mullite grains. In most cases of conventional Al-killed steel grades (Al ≤ 300 ppm), zircon-based filler sands show a sufficient sintering effect, whereas they are not suitable for high-Mn and high-Al steel grades due to the serious sintering result.

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To check the application possibility of zircon grains for high Mn-high Al steel grades, laboratory experiments are carried out to investigate the sintering behaviors of the mixed filler sands of chromite and zircon grains. It is found that the mixed filler sands have a good sintering performance without the impact of liquid steel, and the sintering is continuously accelerated with the increase of zircon addition. During sintering, the zircon grains will decompose into zirconia and SiO 2 , and react with chromite grains to generate a liquid phase. Liquid steel enhances the sintering of the filler sands significantly, and the Mn and Al contents in steel play an important role. In case of high Mn-high Al steel grades, the effect of Mn on the sintering is more remarkable than that of Al, and the mixed filler sands are seriously sintered. Zircon sand grains are not suitable for high Mn-high Al steel grades.