Study on Thermal Deformation on the Microstructural Evolution of 3.45wt.% Si Non-Oriented Silicon Steel Prepared by Sub-Rapid Solidification Method

Abstract

Due to the rapid development of the electrical vehicles, the demand for non-oriented silicon steels, the core raw materials for drive motor, is significantly increasing. The current technology for manufacturing non-oriented silicon steels exhibits characteristics, such as a long process and high energy consumption. Therefore, the development of a shorter process for the production of high-quality silicon steels is urgent. This paper initially prepared a Fe-3.45wt.%Si non-oriented silicon steel as a cast strip sample through the immersion-type sub-rapid solidification method. Subsequently, the strip was hot rolled under different conditions with varying temperatures and reduction rates. Finally, the effect of thermal deformation on the microstructural evolution was analyzed. The results indicate that abundant columnar crystals with a favorable strong {100} texture have been formed in the as-cast strip solidified structure at the superheat of 90 ℃. Then, hot rolling would cause the crystal orientation to rotate from original {100} to {014}<341>, {132}<210> and other Copper textures, with the hot rolling temperature enhancing the recrystallization of the structure. When the rolling temperature is designed at 850°C with a reduction rate of 30%, the hot-rolled strip retains a certain amount of {100} texture while forming stronger {014}<341> and {041}<314> textures, with an average grain size of 175 μm, resulting in an excellent structure that requires a shorter process and less energy compared to traditional technology. Furthermore, the subsequent normalization would further enhance the recrystallization behavior, introducing an obvious refined grain size, which in turn deteriorates the magnetic properties of the finished silicon steel. Therefore, the normalization process necessary in the traditional technology, is not recommended in our proposed technology. This paper would provide guidelines for the development a novel short process for the production of high-grade non-oriented silicon steels.

Keywords: Twin-roll strip casting, Sub-rapid solidification, non-oriented silicon steel, texture, hot rolling