Weather Resistant Steel Plate
Atmospheric corrosion resistant steel, also known as weathering resistant steel, is a kind of lowalloy steel made by adding a certain amount of alloy elements to ordinary steel. The main alloy components are Cu, P, Cr, Ni and other elements. Basic Information： Atmospheric corrosion resistant steel (i.e. weathering resistant steel) is a kind of low alloy steel with good atmospheric corrosion resistance made by adding a certain amount of Cu, P, C or Ni, Mo, Nb, Ti and other alloying elements into the steel. In industrial and rural atmospheric environment, weathering steel forms a layer of dense and stable oxide protective film on its matrix surface, which hinders the entry of corrosive medium and has excellent atmospheric corrosionresistance. However, the rust layer formed by corrosion on the surface of general carbon steel matrix is loose and has micro cracks, which can not really play a protective role on the matrix steel. Corrosion resistance mechanism： From the effect of corrosion products on corrosion process, atmospheric corrosion of steel is a process of electrochemical reaction of oxygen in the air through the rust layer in the presence of water film. The rust layer is composed of loose outer rust layer and dense inner rust layer. The alloy elements in steel mainly act through the influence of inner rust layer. The enrichment of Cu, P and Cr dense inner rust layer can be observed in the corrosion products of weathering resistant steel. The higher corrosion resistance of weathering resistant steel is related not only to the high impedance of the inner rust layer, but also to the dense inner rust layer, the finer grain size and the enrichment of Cu and P. The existence of this dense inner rust layer is reflected in the electrochemical behavior of the steel that the anode process is blocked. This process of gradually improving the densification in the corrosion process just shows that the longer the timethe stronger the corrosion resistance.
Atmospheric corrosion： From a global perspective, the main composition of the atmosphere is basically unchanged. A ccording to the experimental measurement, the composition of the air by volume is about: nitrogen 78%, oxygen 21%, noble gases 0.94%, carbon dioxide 0.03%, other gases and impurities 0.03%. Due to the natural location, climate and other conditions as well as man-made environmental pollution, the composition of the atmosphere has become complicated and diversified, and some harmful components have a tendency to increase gradually. In particular, global acid rain caused by sulfur dioxide and nitrogen dioxide in the air has exacerbated the corrosion of steel materials, even though sulfur dioxide and nitrogen dioxide do not occur naturally. However, the vast majority of these basic air pollutants are produced by human activities. Once the sulfur dioxide and nitrogen dioxide pollution gases emitted by humans enter the atmosphere, they maybe converted into secondary pollutants nitric acid and sulfuric acid, which are easily dissolved in water and return to the ground to form acid rain and acid snow. Different impurity types in the atmosphere have different effects on the corrosion rate of steel. The sulfur dioxide in industrial atmosphere and salt particles in Marine atmosphere have the greatest influence on the corrosion rate of steel. The corrosion rate of steel is very low in the pure rural atmosphere. Atmospheric corrosion of steel is a complex system. In addition to man-made enviro nmental pollution, corrosion rate is also related to wind speed and direction, temperature and rainfall, dew fall period, solar radiation, seasonal change and even natural dust in the atmosphere. Even under the same external conditions, the corrosion rate of the steel backside is significantly higher than that of the sunny side due to the deposition of rain. Rust layer structure： In the use of weathering steel, corrosion occurs at the initial stage, just like that of ordinary steel, but later the corrosion rate gradually slows down, and after a certain time, the corrosion is almost no longer carried out, so as to achieve the purpose of protecting the matrix. This ph enomenon is called the stabilization of the rust layer, and the rust layer in this state is called the stabilization of the rust layer. From the effect of corrosion products on corrosion process, atmos pheric corrosion of steel is a process of electrochemical reaction of oxygen in the air through therust layer in the presence of water film. The rust layer is composed of loose outer rust layer and dense inner rust layer. The alloy elements in steel mainly act through the influence of inner rust layer.
The rust layer is stabilized： (1) Rapid formation of stable rust layer: The primary key of rust layer stabilization technology is how to effectively control early rust corrosion and form a dense and stable rust layer, so as to obtain FeOOH in the coating film. (2) The role of alloying elements: chromium and other metal elements replace goethite to form the final stable rust layer, which generally takes 10 years. How to select appropriate metal element ions to replace iron ions, speed up the replacement speed, and form a stable rust layer in a short time; The second key is to enrich cu, P, cr and other alloying elements in the rust layer. (3) Organic coating materials: The research and development of the rust layer stabilization treatment method has three aspects: weatherproof film treatment, special oxidation coating treatment, iron oxide phosphate system treatment. Whether as a coating material, or as a color carrier or binder, organic matter needs to have good weather resistance and corrosion resistance, the coating material should also have the characteristics of porous grid. It can not only allow a certain amount of air and water to supply the bottom until the formation of a stable rust layer, but also prevent the flow of weathering steel rust liquid, flying, to maintain the appearance of beauty. |
