A Comparative Study of Microstructure and Texture Evolution in Cu-Bearing and Nb-Bearing Grain Oriented Silicon Steels

Abstract

Here, the authors elucidate the microstructure and texture evolution in ultra-low carbon grain oriented silicon steels with (Cu,Mn)S and Nb(C,N) as inhibitors. Both Cu- and Nb-bearing steels exhibit microstructural and texture gradients across the thickness. The surface layer is characterized by recrystallized equiaxed grains, while the subsurface layer is dominated by strong Goss texture, and the center layer is composed of elongated deformed bands with strong α-fiber including {100} ∼{223} texture. In contrast to the Cu-bearing hot rolled sheet, the deformed center zone of Nb-hot rolled sheet is broadened and indicate a new {111} component, while the neighboring Goss zone, which act as the nuclei for secondary recrystallization is reduced. Also, the fraction of Goss texture in Nb-primary recrystallized sheets is lower than Cu-primary sheets in a series of specimens subjected to identical annealing temperature prior to secondary recrystallization because of inheriting texture of hot rolled sheets. On the other hand, compared to the (Cu,Mn)S particles, the Nb(C,N) particles significantly hinder the primary recrystallized grain growth. The onset of secondary recrystallization for Cu-bearing steel is 950 °C, while the growth of Nb-primary grains continue to be strongly inhibited at 975 °C. After high-temperature annealing, a high magnetic induction (B8 is ≈1. 8 T) is obtained in Cu-bearing steel. In contrast, in Nb-bearing steel, there is no secondary recrystallization or the non-Goss grain ({113} ) is abnormal growth, and the magnetic induction B8 is ≈1.48–1.5 T. The lower magnetic induction of Nb-bearing silicon steel is related to the lower fraction of primary Goss texture and the stronger pinning effect of Nb(C,N) inhibitors.