Steel may absorb hydrogen during melting, or during the various steps of applying enamel frit (dipping, drying and firing), metal pickling and dipping, especially in sulfuric acid without corrosion inhibitors, will cause steel to absorb hydrogen. The pickling time depends on the thickness of the rust flakes and the temperature of the pickling solution. The longer the metal stays in the acid, the greater the chance it will absorb hydrogen.

The most important thing is that steel absorbs hydrogen during the enamel firing process, because at high temperatures, hydrogen dissolves the most in metal. During the firing process of the ground coat, a reaction occurs between the iron surface and the water vapor:

Fe + H2O → FeO + H2↑

Hydrogen is easy to dissolve in steel, especially when the enamel is melted and gas cannot escape freely. The main source of steam is water, which is the component of clay, which evaporates below 500°C. The moisture in the atmosphere also has an effect. Therefore, fish scale explosion may also be a seasonal accident, and in spring and summer (rainy) Occurs more often.

The more uniform the structure of the steel, the fewer defects, and the fewer opportunities for the formation of molecular hydrogen. The type of steel affects the capacity to transmit hydrogen. At present, it is common that cold rolled steel is less prone to fish scales than hot rolled steel. In each part of a vessel, the cold processed part (such as the wall of a small pot with a handle) is less likely to have fish scales exploded than the unprocessed part (bottom of the pot). The accumulation of more or less in the steel depends on the diffusion rate, which is the factor that determines the appearance of fish scales.

Different additives in the composition of steel can change the solubility of hydrogen in steel. Copper, carbon, aluminum, and chromium reduce the solubility of hydrogen; nickel, cobalt, manganese, and titanium all increase the solubility of hydrogen in steel.

However, when the same type of steel is coated with different enamel frit under different conditions, the fish scales that occur are also different. If you want to reduce the hydrogen content as much as possible, then pickling must be fast, and corrosion inhibitors (inhibitors) must be added. If the ground coat quickly overflows to the metal surface after the water in the clay is analyzed, the hydrogen formed at this time will be dissolved in the steel. The ground coat with a suitable wide firing range has a certain effect on the suppression of fish scale explosion.

A simple and quick way to test whether fish scales will burst: Put the enameled test piece in a freezer at minus 16°C for 30 minutes, then take it out and put it in a 140°C oven, take it out after 30 minutes, and observe whether there are fish scales on the porcelain surface. Explosion occurs.