Study Of Separation Coating Of Grain-oriented Silicon Steel

Grain-oriented silicon steel is an important and indispensable soft magnetic material in power and electronics industry. Due to its complex manufacturing processes, it’s known as "crafts" in special steel field. To avoid the coil steel from sticking during the high temperature annealing, a layer of refractory materials is needed as separator, which is magnesia commonly,during manufacturing process. And a separation coating (forsterite) is formed from a reaction between the steel surface and the magnesia. The quality of separation coating is affected by the nature of magnesia and the ingredient of separator. And the quality of the separation coating has a great influence on the surface quality and magnetic properties of grain-oriented silicon steel.In this paper, the effects of morphology of magnesia primary particles, as spherical, clubbed and lamellar, on the quality of separation coating and magnetic properties of silicon steel were studied respectively. The results revealed that the properties of magnesia such as secondary particle size, activity and hydration rate are affected by morphology of primary particles of the magnesia, then the performance of separation coating and the properties of silicon steel will be changed correspondingly. A dense separation coating with good corrosion resistance, low iron loss of silicon steel, and high magnetic induction intensity can be obtained by using spherical magnesia,because its less conglobation and good coating performance.The properties of clubbed magnesia are a bit worse than spherical magnesia. While the separation coatings formed from lamellar magnesia was loose, rough, and has a poor corrosion resistance, high iron loss of silicon steel, and low magnetic induction intensity, because the lamellar magnesia is easy to reunite and has a low activity.The influence of silane coupling agent and alumina addition in magnesia slurry on separation liquid, separation coating and the properties of silicon steel are studied. It is found that the silane coupling agent has improved the suspension and uniformity of separation liquid. Then a dense separation coating is formed, due to the magnesia particles are more uniform on the surface of the silicon steel, which lead to an excellent surface quality, corrosion resistance and silicon steel magnetic properties of separation coating. When the content of silane coupling agent was 1%, the apparent mass and corrosion resistance of the separation coating are best, and the magnetic properties and interlayer resistance of silicon steel are improved also. Compared with the content of silane coupling agent was 0, the iron loss decrease 0.04 W/kg when the content of silane coupling agent was 1%, and the magnetic induction intensity increases 7 mT, interlayer resistance increase 260Ω·mm2. The coating properties of separation liquid are improved after adding Al2O3 into MgO separator, and a ground floor of separation coating composed of magnesium silicate spinel is formed, in which the spinel can reduce iron loss and increase magnetic induction of silicon. When the content of Al2O3 was 4%, the apparent mass and corrosion resistance of the separation coating are better, and the magnetic properties, interlayer resistance, and lamination coefficient of silicon steel are also better. Compared with the content of Al2O3 was 0, the iron loss decrease 0.08 W/kg when the content of Al2O3 was 4%, and the magnetic induction intensity increases 0.09T, interlayer resistance increase 200Ω·mm2.