Development of {100} Texture in Silicon Steel Sheets by Isothermal Austenite→Ferrite Transformations and Its Mechanism

An investigation has been made to develop {100} texture in silicon steel sheet by an isothermal austenite (γ) →ferrite (α) transformation. Steel sheets alloyed with approximately 2% of silicon, 1% of manganese and 0.1% of carbon were vacuum-annealed and then decarburized in a 20% hydrogen-argon atmosphere containing water vapor. During the vacuum-annealing at the α/γ duplex-or γ-phase temperatures from 900 to 1050°C, a thin layer just below the surface of the sheet transformed to α-ferrite and a strong texture of {100} <011>or {100} type developed in the layer. By the subsequent decarburization, the α-ferrite grains in the layer grew toward the thickness center of the sheet, forming a columnar grain structure. The resulted columnar grain structure that inherited the texture of the surface α-ferrite layer exhibited an excellent soft-magnetic properties. The γ→α transformation within the surface layer is considered to be due to a long-range carbon diffusion induced by a manganese dilution in the layer. The selective driving force for the strong {100} texture formation is thought to reside in the anisotropy of the surface energy at the annealing atmosphere-metal interface.