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An ultra-low carbon grain-oriented silicon steel as-cast strip is produced by twin-roll strip casting process, and subsequently subjected to one-pass hot rolling, one-stage cold rolling, primary annealing, and secondary annealing. The effect of hot rolling process on microstructure, texture, and inhibitor evolution is studied. It is shown that the precipitation behavior of AlN particles is significantly affected by the hot rolling temperature and the optimal precipitation temperature is ≈1100 °C. On the other hand, the intensity of Goss texture in hot-rolled sheets is determined by hot rolling reduction, which is limited in the strip casting process and the hot-rolled Goss texture is relatively weak compared to the conventional process. The primary annealed Goss texture can originate from the cold rolling process and this texture is homogeneous through the thickness, besides the inherited hot-rolled Goss texture mainly presented in the subsurface layer. Thus, relatively strong Goss texture in primary annealed sheets is obtained. The results indicate that the hot rolling process is an efficient way to optimize the texture and precipitation in strip-cast silicon steel, and relatively good magnetic properties can be obtained by the strip casting process.

Grain-oriented 4.5%Si steel is processed by strip casting and two-stage rolling with second rolling reduction varied from 53.3 to 82.7%. The microstructure and texture evolution are studied with emphasis on the effect of second rolling reduction on secondary recrystallization. After secondary annealing, significant abnormal grain growth occurs for all reductions in the range of 53.3–82.7%. The underlying reason is the strong inhibiting force induced by additional Nb, and the grain diameter of the secondary grains increase with increased rolling reduction. Additionally, the sharpness of secondary grains to ideal Goss orientation increase with increase in second rolling reduction. This is attributed to decreased inhibiting force drop rate between abnormal grain growth of precise Goss and deviated Goss grains with increased rolling reduction. Another interesting aspect is enhancement of magnetic induction B8 and significant reduction in high frequency (400–1000 Hz) core losses with increase in second rolling reduction. Optimal magnetic properties are obtained in the steel subjected to 82.7% rolling reduction. The present study suggests that strip casting is an effective approach to fabricate grain-oriented high silicon steel, especially thin-gauged steels with superior magnetic properties.

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.