Abstract: Epstein frame samples of the silicon steel of 35SW440 were produced by two stress relieving annealing processes of continuous annealing and well annealing. The comparative investigations were conducted on the relationships between the two stress relieving annealing process and their microstructures, precipitation and magnetic properties. The results showed that after stress relief annealing, the iron loss reduced and the magnetic induction improved. Compared with the well type annealing process, the iron core of the steel produced by continuous annealing process had poor magnetic properties under the condition of high magnetic density due to the obvious surface nitriding phenomenon on the surface of the steel. The surface nitriding was due to the unreasonable design of the protective atmosphere and annealing process, resulting in a large number of fine and dispersed AlN precipitates produced in steel. AlN precipitates affected the movement of domain wall and magnetic moment, resulting in the deterioration of magnetic properties. By contrast, the well annealing process reduced the iron loss of the electrical steel sheet under high magnetic density, and improved properties index of iron core due to the effective control of the surface nitriding in steel.
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Key words: nonoriented silicon steel, stress relieving annealing process, microstructure, magnetic properties