Microstructure and plasticity improvement of Nb-microalloyed high-silicon electrical steel

In this paper, the effects of Nb contents (0.05 ~ 0.50wt%) and hot rolling temperatures (1000 ~ 1200 °C) on microstructure and mechanical properties of high-silicon electrical steel were studied. The results show that adding a small amount of Nb can significantly improve the plasticity of high-silicon electrical steel. Compared with the specimens without Nb, the three-point bending load–deflection curves of the alloys with Nb contents of 0.05 ~ 0.50wt% after warm rolling showed obvious plastic stage. The average fracture deflection increases from 4.5 to 9.9 mm with the Nb content increasing from 0.05 to 0.50wt%. When the hot rolling temperature is 1000 °C, the Nb-containing high-silicon electrical steel has a layered microstructure along the thickness direction. The surface layer is equiaxed grains with dynamic recrystallization, while the center of the thickness is a long strip structure with dynamic recovery. The mechanism of Nb microalloying to improve plasticity includes three aspects: Firstly, the layered structure hinders the propagation of cracks and delays the progress of fracture; secondly, a large number of fine Nb precipitates will hinder the grain growth and refine the grains; thirdly, the formation of the Nb-precipitated phase destroys the ordered rearrangement between adjacent Fe and Si atoms in the matrix, inhibits the ordered transformation and reduces the ordered degree of high-silicon electrical steel. When the hot rolling temperature is increased to 1100 °C or above, the layered structure disappears, the grain coarsens obviously, and the plasticity of the warm-rolled specimens is significantly reduced.