The effect of thickness of the hot-rolled sheet on the magnetic properties of non-oriented electrical steel

Abstract

Non-oriented (NO) electrical steel sheets with a thin thickness are drawing interest as potential materials for electric vehicle drive motor cores due to their ability to reduce high-frequency core loss. To produce electrical steel sheets with a thickness of 0.25 mm or less, it is beneficial to minimize the thickness of the hot-rolled sheets. However, it is well known that it is difficult to achieve hot-rolled coils with a thickness of 1.4 mm or less with a conventional hot rolling process. Therefore, the thin slab casting and rolling (TSCR) process is now used to produce thin hot-rolled coils that cannot be produced by conventional methods.In this study, we investigated the effects of hot-rolled sheet thickness produced by the TSCR process and cold-rolling reduction ratio on the crystallographic texture, microstructure, and magnetic characteristics of 3% Si NO steel. The results showed that the textures of the hot-rolled sheet and the annealed hot-rolled sheet are virtually unaffected by the hot-rolling reduction ratio. However, the cold-rolling reduction ratio substantially affects many aspects of NO electrical steels. The recrystallized grain size after the final annealing process decreases as the cold reduction ratio increases, while the magnetic flux density decreases with increasing cold reduction ratio, especially for reductions exceeding 82.8 %.In conclusion, the thickness of hot-rolled steel sheets manufactured by the TSCR process has little effect on the microstructure and texture of hot-rolled sheet. Therefore, reducing the cold rolling reduction ratio, which can be achieved by using thin hot-rolled sheets manufactured by the TSCR process, is a promising method for enhancing the magnetic characteristics of thin-gauge NO electrical steel sheets.