HOME APPLIANCE

Home appliance industry requires food-grade materials with good resistance to corrosion phenomena, the most common coating used for this application is the enamel. The porcelain (vitreous) coating is applied to the steel by a high productivity industrial enamelling process that can be affected by several defects among them the fishscaling, that is considered the most dangerous damage in the production of enamelled steel products. Fishscaling is caused by an excess of hydrogen content in the steel that is produced during enamel firing at a temperature of 800-850°C when hydrogen dissolves into the steel. The solubility of the hydrogen in steel strongly decreases during subsequent cooling but the hydrogen present tends to slowly migrate towards the enamel-steel interface. In the interface region hydrogen concentrates as the ceramic layer prevents the diffusion, thus producing high pressure. As a consequence small chips of enamel pop loose from the layer even after a long time after the end of the product manufacturing. Steel susceptibility to fishscale depends on its microstructure in particular on the content, distribution and nature of site traps that are available for trapping the hydrogen thus preventing its diffusion toward the surface. It was demonstrated that steel resistance to fishscale strongly depends on specific parameters both of manufacturing process and chemical composition of the steel. Steelmakers and Home Appliance industry have to perform quality control of the sheet steel to prevent fishscale defects.