The Role of Temper Rolling and Annealing on the Magnetic Property Improvement of a Low Si Non-oriented Electrical Steel

Temper rollingTemper rolling is a light cold deformation process (normally under tension, with less than ~10% thickness reduction) applied to annealed non-oriented electrical steelNon-oriented electrical steel sheets to improve the surface quality of the final product. The small plastic deformation and the subsequent annealingAnnealing, however, have a considerable effect on the magnetic propertiesMagnetic properties of electrical steels. This is because the strain introduced in the temper rollingTemper rolling process changes the distribution of the stored energy in grains with different orientations, which significantly affects the grain growth and textureTexture development during final annealingAnnealing, thus influencing the magnetic propertiesMagnetic properties. In this study, a low Si non-oriented electrical steelNon-oriented electrical steel was hot rolled, cold rolled, and batch annealed to produce 0.5-mm-thick sheets. Temper rolling (~6% reduction) was then applied to the annealed sheets and annealed again at different temperatures (500–900 °C) for a fixed time (2 h) or at a fixed temperature (800 °C) for different times (0.5–24 h). It was found that temper rollingTemper rolling and annealing could significantly improve the magnetic properties, i.e., decreasing the core loss by up to ~22% and increasing the relative peak permeability by up to 68% at 1.5 T and 60 Hz, as compared to that without temper rolling. The improvement of magnetic propertiesMagnetic properties was correlated to the changes in microstructure and textureTexture induced during the temper rollingTemper rolling and final annealingAnnealing processes.