The thermal expansion coefficient of the metal substrate is greater than that of the ceramic layer, which means that the ceramic layer always has residual stress at room temperature. The residual stress is influenced by the difference in thermal expansion coefficients, temperature, glaze thickness, substrate thickness, and other factors. The residual thermal stress in enamel equipment has been theoretically calculated. When the compressive stress in the ceramic layer is large enough, the ceramic layer may start to peel off. Therefore, when designing the ceramic glaze, its thermal expansion coefficient should be made as close as possible to that of the substrate, while also improving the adhesion between the substrate and the ceramic layer. The adhesion of enamel is directly related to the wetting ability of the ceramic glaze on the metal. The stronger the wetting of the ceramic glaze melt and slurry on the metal, the more favorable it is for the mutual attraction at the interface during spraying and firing, accelerating the chemical reaction to form chemical bonds and enhancing adhesion. Additionally, the ceramic layer is usually uneven and commonly contains inclusions, which is a characteristic of the enameling process. This is because the glaze slurry is made by mixing frits and enameling additives, and the final firing is limited by time, which hinders the complete homogenization of the glassy phase.