Precipitation Behaviors of AlN Inclusion in High-Al Steel

Abstract

High-Al steel was prepared under laboratory conditions. The single-particle AlN and multi-particle aggregated AlN, AlON, AlN–MnS, and Al2O3–AlN–MnS inclusions were observed by FESEM-EDS. The single-particle AlN inclusions are mainly in the form of blocks and strips, with their size mainly concentrated in the range of 1 to 5 μm. The aggregated AlN inclusions are polygonal, toroidal, and irregular in shape and their size mainly concentrated in the range of 1 to 13 μm. The size of AlN–MnS and Al2O3–AlN–MnS inclusions is less than 15 μm. Thermodynamic calculation shows that AlN inclusion precipitates in the two-phase region. Growth kinetics showed that the size of AlN inclusions at the end of solidification ranged from 1 to 7 μm, which is consistent with the observed size of single-particle AlN inclusions. Lattice mismatch indicates that AlN can be as an effective site for MnS nucleation. The equilibrium constant log KAlON= - 137841.3 / T+ 45.49 of AlON inclusions is constructed. Furthermore, the mass percentage changes of inclusions during solidification were predicted based on the microsegregation model combined with the FactSage software.