Abstract: The S-N curve of a high strength non-oriented electrical steel was tested. The microstructure and fatigue fracture morphology and dislocation were analyzed by optical microscope, scanning electron microscope, transmission electron microscope. The results showed that: at room temperature and the frequency of 20 Hz and the stress ratio R of 0.1, the fatigue strength of the experimental steel was 360 MPa when the cycle was 10⁷  cycles. The fatigue crack initiation at the surface of the steel and the intergranular fracture phenomenon occurred. There were cleavage steps and fatigue stripes in the fatigue crack propagation region, and the instantaneous fracture region was ductile fracture with a large number of dimples. A large number of dislocations appeared in the matrix under cyclic stress, and there persistant slip band terminated at the grain boundary position.

Key words: high strength non-oriented electrical steel, fatigue strength, fracture morphology, dislocation