Effect of Normalizing Treatment on Microstructure and Mechanical Properties of Non-oriented Fe-3.0% Si Steel

Abstract

This study focuses on the microstructure evolution of non-oriented silicon steel for the drive motor iron core of new energy vehicles. The Fe-3.0% Si non-oriented silicon steel hot-rolled bands were taken as the research objects and were normalized at 700, 800 and 900 °C for 3 and 10 min. The influence of low-temperature normalization process on the microstructure, texture and mechanical properties was studied. The results show that the bands normalized at 700 and 800 °C inherit the gradient microstructure and texture characteristics of the initial hot-rolled band. The surface layer consists of homogeneous and fine recrystallized grains, the central layer consists of elongated deformed grains with γ-fiber and α-fiber textures and the subsurface layer has mixed grain structure with strong Goss texture. When the normalizing temperature is increased to 900 °C, the normalized band is completely recrystallized, and the gradient structure and texture are significantly weakened. During the normalizing process, the θ-fiber oriented grains in the subsurface mainly nucleate at the grain boundaries of the α*-fiber and <110> //ND matrix grains, and the <110> //ND oriented grains mainly nucleate at the grain boundaries of Goss and {110} <115> deformed matrix grains. The θ-fiber oriented grains in the central layer mainly nucleate at the grain boundaries of {001} <110>, γ-fiber and {114} <481> matrix grains, the α-fiber oriented grains nucleate in the {111} <110> and α-fiber deformed matrix grains, the nucleation of α*-fiber grains is related to the α-fiber deformed matrix grains. After normalizing at 900 °C, θ-fiber and α*-fiber grains have growth advantages, resulting in strong θ-fiber and α*-fiber textures. As the normalizing temperature increases, the gradient structure of the normalized microstructure is gradually weakened, thus leading to the decrease in plastic deformation ability.