Abstract: In order to find out the precipitation behavior of sulfide inclusions and the corresponding changes of microstructure and electromagnetic properties of high sulfur nonoriented silicon steel sheets, so that to design more suitable sulfur concentration controlling limit for industrial manufacture and to release the steelmaking difficulty effectively, the type and composition, the size and number, and the size distribution of sulfide inclusion and the changes of finished sample microstructure and electronmagnetic properties in 0.25 % Si non oriented silicon steel sheets with different sulfur content of 0.006 8 %, 0.010 2 %, 0.025 3 % and 0.035 3 %（mass fraction） were discussed by the methods of electrolysis extraction in a non aqueous solution and SEM/TEM. The results showed that for present work, as the increase of sulfur content from 0.006 8 %  to  0.035 3 %, the types of sulfide inclusions in steel will gradually change from MnS to MnS+Cu2S, even to Cu2S, together with the number increasing, while in terms of  size, some sulfide inclusions will get larger, and some will be found more small repectively, which cause the recrystallization structure of hot rolled strips getting bad and restrain the grain growth in finished steel sheets. And it can be also found that the iron loss and magnetic induction of finished steel sheet gradually get worse as the addtion of sulfur content in steel. That is, when the sulfur content increases by 0.01 % for average, the eddy loss, hysteresis loss will increase by 0.24 W/kg  and  0.41 W/kg  respectively, and correspondingly the magnetic induction will decrease by 0.009 T . But the iron loss can still be kept less than  6.0 W/kg  when the sulfur content gets to  0.010 2 % , and the magnetic induction kept more than  1.75 T  when the sulfur content gets to  0.025 5 % .These important conclusions can help in designing more suitable sulfur content controlling limit in production, which can both decrease the manufacturing cost and increase the production efficiency of steel making, on the premise of satisfying the requirements of high grade customers.

Key words: high sulfur nonsilicon steel sheets, nonaqueous solution electrolysis, sulfide inclusion, precipitation behavior, microstructure, electromagnetic properties