The rolling process of silicon steel requires a certain amount of carbon, but carbon is not good for the magnetic properties of silicon steel. In the process of continuous annealing, the silicon steel is decarburized at about 850 ℃ without oxygen, and the decarburization agent used is water. At this temperature, the cementite (Fe3C) in the steel decomposes, and the dissolved carbon atoms diffuse to the surface of the steel strip and react with water vapor (C + H2O → CO + H2), reducing the carbon content of the silicon steel to 30ppm the following.
The deformed grains in the cold-rolled silicon steel also recrystallize during the annealing process, but because MnS and AlN are distributed at the grain boundaries, the growth of the recrystallized grains is strongly inhibited, so the continuous annealing obtains a large number of tens of microns size of small grains.
The continuous silicon steel strip passes through a 300-meter-long continuous annealing furnace, undergoes annealing and cooling processes, and is coated with a magnesium oxide coating (a magnesium silicate glass coating is formed on the surface of the silicon steel to prevent the silicon steel from sticking during high-temperature annealing, improving the Silicon steel surface resistance), re-cut, and coiled into steel coils.
