Effects of Two-Stage Cold Rolling Schedule on Microstructure and Texture Evolution of Strip Casting Grain-Oriented Silicon Steel with Extra-Low Carbon

A 0.27 mm-thick grain-oriented silicon steel sheet with extra-low carbon was successfully produced by a novel processing route including strip casting, normalizing, two-stage cold rolling with an intermediate annealing, primary annealing, and secondary recrystallization annealing. The evolutions of microstructure and texture along the whole processing route were investigated with a special emphasis on the effects of two-stage cold rolling schedule. It was found that Goss orientation originated in the first cold rolling due to shear banding and relatively strong Goss texture evolved through the whole thickness after intermediate annealing. This is significantly different from the results in conventional process in which the origin of Goss texture is in the hot rolling stage and Goss texture only develops below the sheet surface. Besides, it was found that cold rolling schedule had significant influences on microstructure homogeneity, evolution of lambda-fiber texture in primary annealed state and, thus, on secondary recrystallization. In case of appropriate cold rolling schedule, a homogeneous microstructure with Goss texture, relatively strong gamma-fiber texture and medium alpha-fiber texture was observed in the primary annealed strip. Although Goss texture in primary annealed state was much weaker than that in two-stage route in conventional process, a perfect secondary recrystallization microstructure was produced and the magnetic induction B-8 was as high as 1.85 T. By contrast, when the cold rolling schedule was inappropriate, the primary annealed strips exhibited inhomogeneous microstructure, together with weak gamma-fiber texture, medium alpha-fiber and lambda-fiber texture. Finally, the sheets showed incomplete secondary recrystallization microstructure in which a large number of fine grains still existed.