Analysis of Pitting Defects of Magnesium Chromate Insulating Film on Non-oriented Silicon Steel

The magnesium chromate insulating coating of non-oriented silicon steel plate was prone to some pitting defects,which had affected surface quality and performance of the insulating coating.In this paper the morphology of the pitting defects coating and the components difference between the pitting defect location and normal location had been investigated by using SEM/EDS.The results showed that the pitting defects mainly occurred in the pit of the substrate,the contents of Cr,Mg and O at the pitting defect location were significantly higher than that at normal.The structure of pitting defect location was similar to the "volcano" or "crater" structure.At the cove,the coating dropped off seriously,the thickness of the coating decreased from the center to the surrounding with many cracks.Some solid particles suspended in the coating were main contributor to the pitting defects.The preferred raw paint materials,strict production process,and the installation of a vacuum filtration equipment were expected the effective measures to remove the pitting defects.