Thin Solid Films, Vol.443, No.1-2, 33-45, 2003
An analysis of the microstructure and interfacial chemistry of steel-enamel interface
The microstructures of interface between the enamel and the hot-rolled steel pretreated with and without the NiO precoat has been investigated. The microstructure obtained in the sample with the NiO precoat consisted of an intricate network of Fe-Ni metallic rich phase dispersed in the matrix of a glassy phase, and a complex intergrowth inside large gaseous bubbles. Transmission electron microscopy examinations revealed that the large metallic Fe-Ni-rich phase consisted of the colonies of crystals containing spinel NiFe2O4, whereas the intergrowth were composed of nanocrystalline FeO and metallic (Fe,Ni) particles with a large concentration of carbon in the form of a graphite film. In samples without the NiO precoat, there was a complete absence of large dispersed metallic phase and large bubbles at the interface. Moreover, the presence of an oxide layer on the surface of the steel pretreated with the NiO precoat was identified by the selected-area diffraction analysis. In the absence of NiO precoat, however, only individual oxide particles were observed. Based on the experimental evidences and thermodynamic analysis of reactions at the interface, the investigation explains the reasons for an extensive dispersion of the metallic Fe-Ni-rich metallic particulates and the large bubbles encapsulating oxide and metallic phases. These differences in microstructure, especially carbon precipitation. account for the role of NiO in reducing the fish-scaling tendency. (C) 2003 Elsevier B.V. All rights reserved.