Formation process of forsterite film in grain-oriented silicon steel manufactured by acquired inhibitor method

The forsterite film of oriented silicon steel is an important part of product structure. The control of forsterite film is not only a process difficulty, but also a bottleneck of improvement of product performance. However,there are few previous studies on the formation of forsterite film, and there is a lack of theoretical support for the development and quality improvement of thin standardized high-performance products of high magnetic induction oriented silicon steel. Therefore, the formation process of forsterite film in grain-oriented silicon steel manufactured by the acquired inhibitor method was simulated by a high temperature annealing interruption experiment, and the microstructure and composition evolution of forsterite film during annealing were analyzed. The reaction formation process of forsterite film during high temperature annealing was clarified. The Mg₂SiO₄ particles nucleate on the surface of the steel at about 900 ℃ and grow up as the increase of annealing temperature. Up to 1 050 ℃, the Mg₂SiO₄ particles begin to become compact, and the densification process finishes at about 1 100 ℃. The key temperature for the formation of forsterite film is 900-1 100 ℃. In addition, the Al₂O₃·MgO spinel is formed under the forsterite film that can make a "pinning effect" on the forsterites film. During the formation of forsterite film, the Mg²⁺ of MgO diffuses from the surface to the oxide film and reacts with SiO₂. At the same time, SiO₂ in the oxide film matures. The content of Al released by AlN decomposition in the substrate above 1 000 ℃ reacts with Mg₂SiO₄ to form spinel. The excellent forsterite film structure is formed by the original decarburization annealing oxide film surface layer 1 μm to form dense Mg₂SiO₄ and the rest 2-3 μm thickness into a certain amount of ellipsoidal Al₂O₃· MgO spinel for "pinning" bonding layer. Its main control directions are, improving the activity of oxide film, selecting high activity MgO, adding low melting point reaction additives, etc.