Thermogravimetric and Metallographic Investigation of the Oxidation of Steels for Enamelling

According to a survey of the enterprises engaged in enamelling, the Hungarian enamelling industry used 15,000 tons of raw materials in the year 2001 while the total production value reached 10 billion HUF. 71 % of the raw material used was of domestic production. DUNAFERR Company Group manufactured 99% of the utilised enamelled steel. The household equipment represents the greatest part of the enamelled products at which the esthetical feature of the enamel is very important. One of the basic requirements of the exceptional coating is the raw material with good enamelling properties. The newly developed energy efficient and environmental friendly enamelling technologies and the demands for a better ductility make necessary the development of new materials. The advantages of the new materials can only be exploited by knowing thoroughly their characteristics. One of these determinant characteristics is the oxidation behaviour of the base metal. It is well known in the enamelling industry that the oxidation of the of the steel sheets influences the strength of the bond between the enamel and base metal and plays an important role in the formation of the enamel failures. In the final technological step of the enamelling - which is the firing - the steel substrate contacts the wet furnace atmosphere via the dry and porous enamel, and a three-layered iron oxide forms on its surface. The structure and composition of the oxide layer are mainly determined by the quality of the raw material, the characteristics of the surface, respectively the conditions of the oxidation. The thermogravimetric analysis is the most adequate method for studying the oxidation behaviour of the base material.