Characterization of chemical information and morphology for in‐depth oxide layers in decarburized electrical steel with glow discharge sputtering

A combination of scanning electron microscopy, X‐ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy with a sampling method by glow discharge sputtering was successfully employed to characterize the chemical information and microscopic features of oxide layers formed during decarburization annealing of electrical steel in the depth direction at high resolution. The discontinuous surface oxides consisted of SiO₂, (Fe,Mn)SiO₃/(Fe,Mn)₂SiO₄, and FeO. SiO₂ embedded in the (Fe,Mn)₂SiO₄ at the surface may be developed by the preferential nucleation and growth kinetics. The discrete or often relatively spherical oxides of internal oxidation by the energetically favorable surface effect were identified as a mixture of SiO₂ and (Fe,Mn)₂SiO₄ at a depth of ~0.5 µm from the surface. The oxides of networks and small particles at a depth greater than ~1 µm were solely silica, of which the morphologies were possibly caused by the enhanced diffusion of oxygen atoms and Si atoms at grain boundaries or sub‐grain boundaries. The equilibrium and kinetic considerations served by theoretical calculations were introduced to understand the formation and behavior of the observed in‐depth oxidation. Copyright © 2013 John Wiley & Sons, Ltd.