Influence of rapid heating on the oxide layer and magnetic properties of non-oriented electrical steel
A new energy vehicle-oriented non-oriented electrical steel cold-rolled sheet with a silicon content of about 2.9％was selected as the research object.Continuous annealing simulation experiments were conducted in industrial nitrogen atmosphere(with an oxygen content of 0.5％)and high cooling rates.Afterwards,the samples were clas-sified,and 6 representative annealed sheets with 6 different oxidation levels were chosen.The optical microscopy(OM),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),and magnetic property analy-zer(MPA)was used to measure the iron loss and magnetic flux density of the samples before and after acid pickling under high frequency conditions,and the structure of the side oxide layer was observed.The influence of the oxide layer structure and magnetic properties at high heating rates was analyzed.The results showed that for the Non-ori-ented electrical steel with a relatively high silicon content of Fe-Si alloy,under high heating rates,the oxide layer was mainly composed of common Fe2SiO4,usually found between the oxide scale and the substrate.The thickness of the inner oxide layer ranged from 0.2 μm to 1.4 μm,while the outer oxide layer thickness ranged from 0.5 μm to 8.2 μm,with the thickness of the inner and outer oxide layers being proportional.Under fast heating conditions,most samples showed an increase in iron loss after acid pickling,with reduced magnetic flux density and deteriorated magnetic properties.Regarding magnetic flux density,the relative change in magnetic flux density for all samples with different oxidation levels was less than 3％,indicating insignificant changes.Samples with an oxidation level of 5 showed the greatest impact on magnetic properties due to the distribution of Fe2SiO4/FeO phases in a grid-like structure near the grain boundaries of magnetite crystals,while samples with other oxidation levels had lesser impact.
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