Abstract: The surface quality of grain oriented silicon steels is another most important key factor that controls the final qualities of steel products. When the magnetic properties are checked to be satisfactory, the poor surface quality could lead to the degrading or even abandonment of products. Bare grains, water marks, indentations, etc, are all typical surface defects of grain oriented silicon steels during their developments. This paper aims to examine and analyze the point indentations occurred in the final surface sheets of grain oriented silicon steel so as to provide basic features of point indentations and possible reasons of their formation. For this purpose, laser confocal microscopy, scanning electron microscopy, energy dispersive spectroscopy and electron backscatter diffraction technique are used. It is shown that the holes of indentations contain mainly insulating materials, whereas their surroundings are much rich in Fe element of sheet matrix. The compositions of both positions are different to those of normal insulating layers away from them. Based on these features and the facts that the no trace of deformation or recrystallization with fine grains are observed in the interior steel matrix directly located below indentation hole, it is suggested that the investigated indentations should be caused by either the inhomogeneous point defects of oxide layer or inhomogeneous MgO layer which form as hard particle objects and induce a strong plastic deformation in the soft steel sheets during high temperature annealing.

Key words: grain oriented silicon steels, indentation marks, surface defects, insulating layer