What are the characteristics of the corrosion of steel?

Update:12 Mar 2018

    Color coated plate, color plate, color coated roll, […]

    Color coated plate, color plate, color coated roll, color steel coil exposed to the atmosphere. Mainly dry corrosion, wet rot and wet corrosion occurred.
Dry corrosion of steel means that the steel does not form a continuous electrolyte water film on the surface at a relative humidity of 40% in the atmosphere. In this case, the corrosion rate of galvanized steel is slow, but this is less. The wet corrosion of steel refers to the corrosion of steel in the atmospheric environment where the relative humidity is greater than 30% and less than 100%. In this case, there is dust on the surface of the steel. There are pores and cracks in the rust layer and microscopic adsorption occurs to form a water film that is invisible to the naked eye. Electrochemical corrosion occurs under the water film, and the corrosion rate is relatively fast. Wetting corrosion of steel refers to the corrosion of steel in the presence of a condensed, macroscopic water film in a humid atmosphere with a relative humidity of greater than 100%. In this case, the steel surface is thicker, so that the dissolution rate of oxygen to the steel surface is slower and reduces the corrosion rate.
    In fact, corrosion of steel is inseparable from the water film on the surface. Because of the presence of water, oxygen is dissolved in the water, and iron ionizes, causing a series of ionization reactions.
    The oxygen in the air is continuously dissolved in the water and the reaction continues. Because the main product of the reaction, Fes Oa, is red, the iron-oxidized product is generally called "red rust." The red rust is loose and easily dissolved, and it is difficult to protect the surface of the steel from being continuously eroded, so that the corrosion of steel continues until it is completely eroded. This is a characteristic of steel corrosion, and because of this, steel must be coated with other metal or non-metal protective layers to effectively prevent the corrosion of steel.