Whole Process Microstructure, Texture Evolution of Low-temperature HiB Steel and Its Finished Magnetic Properties

Taking the hot-rolled sheet, normalized sheet, cold-rolled sheet, decarburized and nitrided sheet and finished sheet of low-temperature HiB steel in the whole production process as the research object, the microstructure and texture of low-temperature HiB steel were characterized by optical microscopy, X ray diffractomer (XRD) and electron back scatter diffraction (EBSD).The evolution law of microstructure and texture throughout the production process of low-temperature HiB steel was analyzed to explore its impact on the magnetic properties of the finished sheet.The results show that the microstructure and texture of hot-rolled sheet and normalization-annealed sheet of low-temperature HiB steel are significantly different in thickness direction. Goss grain originates from the 1/4 surface layer of hot-rolled sheet, and the texture types of hot-rolled sheet and normalization-annealed sheet are the same, with only differences in the texture strength, and the main texture of the center layer is 118<110>. The cold-rolled sheet has a fibrous deformation structure, forming strong α fiber texture and γ fiber texture, and the texture strength of 111<110> is the highest, at 14.4. The decarburized and nitrided sheet is mainly composed of α* fiber and γ fiber textures, which are 114<481> and 111<112>, respectively. Goss grains are mainly surrounded by 114<481> and 111<112> oriented grains, which are smaller in size than other grains and do no numerical and growth advantage. The finished sheet with magnetic properties of B₈≥1.89 T and P_1.7/50≤0.97 W/kg has well-developed Goss grains, with grain size reaching centimeter level, serrated grain boundaries, and Goss texture is sharp. The finished sheet with magnetic properties of B₈=1.83 T and P_1.7/50=1.27 W/kg is mostly composed of abnormally grown non-Gaussian and Gaussian oriented grains with large deviation angles, and the grain boundaries are smooth. The microstructure of the finished plate without secondary recrystallization of most grains is fine grain structure, with magnetic properties of B₈=1.77 T and P_1.7/50=1.48 W/kg.