Dissolution behavior of AlN in CaO–Al2O3–BaO–CaF2–Li2O system mold fluxes

The dissolution behavior of AlN in three CaO–Al2O3–BaO–CaF2–Li2O non-reactive mold fluxes which were designated as N1 (low break temperature), N2 (good lubrication performance), N3 (high break temperature) for high-Al steel with different requirements was explored by static method. The sizes of AlN rods after dissolving in three slags decreased to 8.35 mm, 7.90 mm, and 9.10 mm, from the initial 10 mm, resulting in 0.59 wt.%, 1.78 wt.%, 0.01 wt.% decrease in Li2O content and 1.60 wt.%, 4.33 wt.%, 0.26 wt.% increase in Al2O3 content in the slags which were in contact with AlN, respectively. The interfaces between slags and AlN rods was investigated by field emission scanning electron microscopy. The results confirmed that the widths of the element transition layer were 6.3 μm, 8.0 μm and 5.3 μm for slags N1, N2, and N3 which were in contact with AlN, respectively. Furthermore, the product at the interface close to the slag sides were Al2O3–CaO–BaO–CaF2 complexes, while close to the AlN rod sides, individual Al2O3 and AlN–Al2O3 complexes were found. The thermodynamic calculation showed that only Li2O in molten slag reacted with AlN to form Al2O3. Thus, the dissolution behavior of AlN in three slags was that AlN reacted with Li2O to form Al2O3, which then diffused into the slags and was absorbed by the slags. In addition, the slags N1 and N2 with lower initial Al2O3 content had a stronger reactivity with AlN, they have a more superior ability to dissolve AlN inclusion.