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Necessity of corrosion-resistant castings

Edit:Xiangyang Liqiang Machinery Co., Ltd.UpDate:2019-06-10

      The factors that cause corrosion are diverse. Once the steel structure is rusted, it will become more and more serious. As a result, the cross-sectional area of the component will decrease and the load carrying capacity will decrease. It will gradually lose its use value and be discarded. Although the corrosion of steel structures currently in use is unavoidable, the corrosion rate is controllable, which requires corrosion-resistant castings.

       Corrosion-resistant casting materials Its own influence

      different metals Has different electrode potentials and different metallographic structures They have different stability (ie corrosion resistance), while steels of the same chemical composition have different corrosion resistance due to different heat treatment processes. In addition, the metal treatment may cause unevenness of the internal electrode potential of the metal and accelerate the corrosion of the metal due to uneven thermal stress distribution during processing such as forging, casting, electric welding, or grain deformation during hot working. The metal itself.

        Corrosion-resistant Cast surface finish state

         It also has a significant effect on the corrosion rate. Especially at an early stage, the smoother the metal surface, the better the corrosion resistance. The rough metal surface becomes an anode because the deep concave portion is not easily contacted with oxygen, and the surface becomes a cathode, causing corrosion of the oxygen concentration battery.

        Impact

         Generally, as the temperature rises, the metal in the electrolyte solution Increase erosion rates. For every 10 °C rise in seawater temperature, the corrosion rate of the steel will double as the electrode reaction increases with increasing temperature.

       The effect of concentration

      For example, seawater is a natural electrolyte solution with various salts. Further comprising a biological precipitate, dissolved gases, organic substances and the like deterioration. However, important factors affecting the corrosion rate of steel are seawater salinity, high salinity, high electrical conductivity, increased corrosion current intensity of macroscopic cells, and increased corrosion of steel. In addition, the presence of large amounts of chloride ions in seawater can also hinder or even destroy the passivation of metals and promote corrosion of metals.

       Corrosion-resistant castings and other factors

       Corrosive media and other factors Accelerated corrosion of metals. Because the atmosphere contains N2 and various impurities, in addition to O2, H2, such as salt spray near the ocean, SO2, H2S chemical zone, as well as various soot, metal compounds and other salt particles. Once the medium falls on the metal surface, it will condense with water, accelerating the corrosion of the metal.

 

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