Abstract: Based on the typical composition of highgrade nonoriented silicon steel, the influence of Mn and Al changes on the equilibrium precipitated phases were studied through thermodynamic simulation calculations. The results showed that the main equilibrium precipitated phases of the highgrade nonoriented silicon steel are AlN, FCC#2, MnS, M3P, M7C3, M23C6 and cementite, FCC#2 phase is a Ti(C,N) compound, and M7C3 and M23C6 are compounds with high Mn content. As the Mn content increases, the transition temperature of MnS precipitation increases sharply. When Mn content is high, with the decrease of temperature, the M7C3 phase will firstly transform into the M5C2 phase then into the M23C6 phase. With the increase of Al content, the transition temperature of Ti (C,N) compounds decreases; the AlN precipitation transition temperature increases. the Al content has a smaller effect on the MnS, M3P, M7C3, and M23C6 phases.

Key words: high grade non oriented silicon steel, thermodynamics, equilibrium phase