Texture Optimization for Intermediate Si-Containing Non-oriented Electrical Steel

Columnar grains can be obtained by decarburization annealing in the two-phase region of Si-containing non-oriented electrical steel under wet-mixed atmosphere. However, iron oxidation or oxidation of alloying elements on the surface hinders the decarburization process and, consequently, the preferred microstructure and texture evolution. This study aims to optimize the texture and obtain excellent magnetic properties in intermediate Si-containing non-oriented electrical steel by process adjustments, such as final annealing under pure hydrogen atmosphere and coarsening initial microstructure by hot-band annealing. First, pure hydrogen atmosphere is used to weaken the surface oxidation layer and to promote the effect of anisotropic strain energy. Driven by anisotropic strain energy during phase transformation, a number of {100}-nearly oriented columnar grains are obtained. Second, high amounts of non-gamma fiber-oriented recrystallized grains, which strongly influence the final transformation texture, are observed during the rapid heating process in the final annealing because of the coarse initial microstructure. Non-gamma fiber-oriented grains grow from the surface into the center layer along the normal direction and form poor columnar grains by carbon diffusion during slow austenite to ferrite (γ → α) transformation in final annealing under pure hydrogen atmosphere. A notable increase in magnetic properties is observed, with magnetic induction at 5000/Am (B ₅₀) above 1.76 T and core loss at 1.5 T by 50 Hz (P _15/50) below 2.6 W/kg.