Evolution of microstructure and texture in grain-oriented 6.5%Si steel processed by strip-casting

Grain-oriented 6.5%Si steel was produced by strip-casting, followed hot rolling, cold rolling, primary annealing and secondary annealing. Microstructural and textural evolution was studied with particular focus on the effect of solidified microstructure on the ultimate microstructure and texture. The study indicated that solidified microstructure of the as-cast strip was determined by melt superheat. The relatively low melt superheat resulted in fine equiaxed grains with random texture, whereas large melt superheat led to coarse grains with moderate λ-fiber texture. After cold rolling, the fine-grained steel showed narrow pancake grain structure in comparison to the coarse-grained steel, which was similar to the microstructure of the initial as-cast strip. After primary annealing, fine equiaxed microstructure with favorable {111}⟨112⟩ texture was obtained in the fine-grained steel. While inhomogeneous microstructure with strong α-fiber and moderate γ-fiber texture was obtained in the coarse-grained steel. The desirable microstructure and texture in the fine-grained steel led to abnormal grain growth with B8 = 1.65 T after secondary annealing. By comparison, normal grain growth occurred in the coarse-grained sample with B8 = 1.37 T. Another observation was high frequency core losses of grain-oriented 6.5%Si steel sheet with adequate secondary grains was significantly lower than non-oriented 6.5%Si steel and grain-oriented 3.0%Si steel. The study suggests that the strip-casting is a suitable route to fabricate grain-oriented 6.5%Si steel, and the initial fine grain size with random texture is preferred to obtain adequate abnormal grain growth.