1. Corten-A high weather resistance and corrosion resistance plate is the abbreviation of weather resistance, corrosion resistance and high tensile strength steel.
Among all metal materials, steel is the most familiar to us. Because steel has high tensile strength and is easy to bend, cut, drill and weld, it is widely used in various buildings and industrial facilities. However, one of the problems that bothers people the most about steel is "corrosion and rust." Therefore, how to prevent corrosion has become a major topic studied by experts. There are many methods to prevent corrosion. Generally speaking, they can be divided into three types. The first method is to apply a layer of substance on the surface of steel to isolate the contact between the steel and the environment and prevent corrosion. The second type is potential anti-corrosion rust. The third type focuses on changing the material of steel to achieve the effect of resisting corrosion. The COR-TEN steel introduced in this article is an example of the third anti-rust method.
Corten-A steel was first used in buildings in 1958 because of its anti-corrosion properties. It was subsequently used in bridges, trains, cars, trucks and industrial facilities, and its uses have become increasingly widespread. In terms of bridge applications, for example, in the United States and Japan, the Arakawa Steel Bridge recently constructed in Tokyo Bay, Japan, is 840 meters long and is entirely constructed of Corten-A steel.
2. Types and chemical composition of Corten-A
Corten-A, a kind of weathering steel, is made by adding a little copper, chromium, phosphorus, and other elements to ordinary steel and undergoing special treatment. Its weathering and corrosion resistance is three to three times higher than that of ordinary steel. Eight times. According to different types and uses, Corten-A can be divided into four types: COR-TEN A, COR-TEN B, COR-TEN C, COR-TEN B-QT. Among them, the weather resistance and corrosion resistance of COR-TEN A is five to eight times better than that of ordinary steel, while the weather resistance and corrosion resistance of COR-TEN B is four times better than that of ordinary steel.
3. Anti-corrosion principle
The excellent atmospheric corrosion resistance is due to the formation of a dense rust layer on the surface of the steel, which isolates the steel matrix from the air and effectively prevents the continued growth of rust. The special elements contained in COR-TEN form an oxide film after contact with the atmosphere. This strong film isolates COR-TEN from the outside world and is no longer affected by the climate, achieving the purpose of weather resistance and corrosion resistance. When Corten-A or ordinary steel is exposed to the atmosphere and comes into contact with moisture and oxygen, the following chemical reactions will occur:
Fe+0.502+H2O→Fe(OH)2
2Fe(OH)2+0.502+H2O→2Fe(OH)3
There is a strong film on the outside of Corten-A steel material, which blocks moisture, oxygen and chemical reactions with the steel material. As for why Corten-A contains a small amount of copper, chromium, phosphorus, etc., it can form a protective film. So far, The jury is still out, but we can get some inspiration from the following points:
(1) There is almost no FeOOH (the experimental formula of Fe2O3.H2O) in the base layer of Corten-A, and a solid oxide film is formed between the FeOOH layer and several base layers. However, this is not the case with ordinary steel materials. FeOOH is even generated directly on the base layer, thus causing cracks and subsequent peeling.
(2) The oxide film between the FeOOH layer and the base layer is radiographically amorphous. (3) Copper, chromium, and phosphorus are all concentrated on the amorphous layer, while sulfur is evenly distributed on this oxide film in the form of sulfate radicals. The comparison of the corrosion rate of Corten-A steel material and general steel material can be expressed by two exposure tests. The first experiment was done in Kenney, New Jersey, USA, and the second experiment was done in Hyogo Prefecture, Japan (both experimental locations are industrial areas). Corten-A (corten steel) corrosion stopped after three to four years of testing, while other experimental steel materials continued to corrode. The formation of oxide film is related to climatic factors. Generally speaking, climate factors include: temperature, sunshine time, humidity, rainfall, wind speed, carbon dioxide and salt content in the atmosphere, etc. Usually these factors are directly proportional to the corrosion rate. According to experiments done in Cape Ashizuri, Shikoku, Japan, the temperature, humidity, and salinity are all high. The corrosion rate of general steel reaches 0.75 mm per year, while the corrosion rate of Corten-A is 0.75 mm per year. Only 0.25mm. The experiment lasted eight years, but after five years, the corrosion rate of Corten-A was greatly reduced, while ordinary steel continued to corrode. General estimate. In Japan, it takes about five to eight years to form a stable oxide film, while in Taiwan it takes about eight years.
therefore. Due to differences in region, environment and climate factors, the time it takes for a solid oxide film to form on the surface of Corten-A also varies greatly. In order to form this stable oxide film as early as possible, usually when using COR-TEN in island countries, weather-coated treatment-ment is required to make it easier for COR-TEN to exert its weather-resistant and anti-corrosion properties.
