Test as-cast grain-oriented silicon steel (/% : 0.044-0.056C

3.12-3.32Si

0.08-0.11 Mn

0.002-0.008S

0.0029-0.0291 Als

0.0062-0.0109N) is melted by a 30 kg high frequency vacuum induction furnace. The research results by using field emission-scanning electron microscope/energy dispersive spectrometer (FE-SEM/ EDS) show that in 0.0029% Als steel the main oxide is SiO

2

and there is independent laminable

rod-like and approximate spherical shape MnS while the oxide or nitride bearing aluminium has not been found in steel ； in 0. 0090% Als steel the composite oxide containing prime A1

2

O

3

occurs and there is MnS-AlN compounded precipitate; with increasing Als in steel the

compounded precipitate develops in a cluster form.The oxide particle is easily becoming a nucleus of MnS-AIN compounded precipitating

and the lower Als content in steel the higher MnS content in inclusion； the smaller oxide as nucleus the more regular morphology of formed compounded inclusion and smaller its size. The thermodynamic calculation results show that the Als content in steel is the main factor to influence on the ingredient of oxide inclusion in steel and the precipitating temperature and amount of AIN in steel.