Phase Structure and Corrosion Resistance of Multilayer Low-Temperature Sintered Chemically Reactive Enamel Coatings

Abstract

The phase structure and corrosion resistance of uncoated, pure enamel-, double-enamel- and triple-enamel-coated hot-rolled plain steel bars were investigated by X-ray diffraction (XRD), laser microscopic Raman spectroscopy, open-circuit potential (OCP), electrochemical impedance spectroscope (EIS), and potentiodynamic polarization curves. Raman spectroscopy tests demonstrated that the crystal phase is dominant on the surface, whereas the amorphous phase was observed in the cross-sectional area and decreased with an increase of distance from the steel-coating interface. The crystal phase decreased and there was almost no amorphous phase after immersion in 3.5% by weight NaCl solution. Electrochemical tests showed that both double-enamel- and triple-enamel-coated steel bars had approximately similar corrosion resistance, which was higher than that of pure enamel-coated steel bars.