| In this dissertation, through adding favourable element, hot band normalizing, changing manufacturing parameter of cold rolling and annealing, thin non-oriented electrical steel sheets (thickness of 0.2mm) with high magnetic properties have been manufactured successfully. The magnetic properties of these products have achieved the level of 20HTH1200, the same grade product of NSC, and satisfied requirements in China. The effects of hot band normalizing, cold rolling and annealing process, grain boundary segregation on magnetic properties, grain size, texture, precipitation have been analyzed and discussed.The experimental results showed that normalizing could make the structure of hot band more uniform and reduce the core loss obviously, but it had little effect on the magnetic induction. As the normalizing temperature increased the grain size of final product was larger and became more even, but the grain became overlarge and uneven if normalized at overhigh temperature. The best normalizing temperature was between 900℃and 950℃. The proportion of{100}texture and (110)[001] texture increased and the proportion of{111} texture decreased when increasing the normalizing temperature.The research on cold rolling process showed that because of the overhigh reduction the proportion of{111} texture in final product was very high and the magnetic properties were bad when using single-stage cold rolling process. When using two-stage cold rolling process, the proportion of{111} texture was also high with the overhigh or overlow second cold rolling reduction. The best magnetic properties were obtained when the second cold rolling reduction was between 55% and 70%.The addition of Tin could reduce the core loss and it also make the magnetic induction reduce, the effects were related to the content of Tin. There was little effect on the core loss and magnetic induction when the content of Tin was 0.05%. When the content was increased to 0.1% the core loss and magnetic induction reduced obviously. When the content reached 0.15% the magnetic induction had little change compared with adding 0.1% Tin, but the core loss increased a little. As the content of Tin increase the proportion of{111} texture in final product decrease obviously as well as the grain size. Because the grain boundary segregation of Tin could reduce the grain boundary energy the nucleation and grain growth of{111} nucleus at the original grain boundary were restrained. We found that the distribution of Tin at the grain boundary was no equal and was proportional to the content of Tin. Different specimens had different average contents of Tin at at the grain boundary, the normalized band after annealing at 700℃for 5 hours was the highest, the final product was the medial and the normalized band was the lowest.TiN precipitate pin at the grain boundary in the final product was observed. The TiN precipitate could block the movement of magnetic domain, which was bad to the magnetic properties. So it’s better for the magnetic properties to reduce the content of Ti in electrical steels as much as possible. There were MnS precipitates with different quantity and size in hot band and normalized band. The quantity of MnS precipitates in hot band was higher than normalized band, the size of MnS precipitate in normalized band was larger. Normalizing can make small MnS precipitates in hot band congregate and enlarge, it is benefit for the grain growth in final annealing process and the movement of domain-wall in final product. |
