Microstructure and adherence of cobalt containing and cobalt free enamels to low carbon steel

Microstructure and adherence correlation of the enamel/steel interface in cobalt containing (CCE) and cobalt free (FCE) enamels was investigated. Results showed formation of small islands in the interfaces of the two samples. Consequently, the adherence mechanisms can be explained by the dendritic and chemical theories in both samples. Also cobalt and nickel oxides in enamels were reduced to the metallic state by base metal during firing. CCE showed stronger adherence than FCE due to higher amount of Co, in compare with Ni, migrated from the glass to steel. According to the electrolytic theory Co and Fe ions exchange in the interface leading to coarser roughening of the metal in the interface and hence, effectively increased the adhesion strength in CCE.