Effect of Partial Recrystallization Annealing on Magnetic Properties and Mechanical Properties of Non-Oriented Silicon Steel

With the rapid development of high-speed motors, traditional non-oriented silicon steel is difficult to meet its strength requirements. High strength enables resistance to deformation and fatigue fracture induced by centrifugal force. In this work, Nb element is added to traditional non-oriented silicon steel to improve its strength without greatly sacrificing good magnetism. The previous research on Nb-containing high strength non-oriented silicon steel showed that the annealing at high temperature led to good magnetic properties but poor mechanical properties. In order to improve the strength of the steel, the annealing temperature was decreased to make part of the dislocation structure retained in the cold rolled material. The influences of annealing below 900 degrees C on the microstructures, texture, magnetic and mechanical properties of cold rolled Nb-alloyed non-oriented electrical steel were investigated in this work. The increase of annealing temperature promoted recovery at 700 similar to 750 degrees C and led to a partial re-crystallization with higher fraction at 800 similar to 850 degrees C; meanwhile, alpha texture component was enhanced but gamma texture suppressed with the increasing temperature. In contrast, the annealing at 900 degrees C resulted in a complete recrystallization, stronger gamma but weaker alpha texture component. Higher annealing temperature produced lower strength and higher ductility as expected, due to dislocations annihilated by recovery and recrystallization, which also led to lower high-frequency iron loss. The value of magnetic induction B-50 corresponds well with the intensity of alpha texture in the annealed steel, and reaches the maximum value at 850 degrees C due to the most intense alpha texture formed, at which the best combination of mechanical and magnetic properties is also achieved, including the value of magnetic flux B-50 (1.572 T), high-frequency iron loss P-1.0(/400) (33.26 W/kg) and yield strength about 600 MPa, the latter is attributed to the multiple strengthening mechanisms including dislocation, precipitation and grain refinement strengthening.