1. Corrosion resistance

Stainless steel contains chromium. When chromium is oxidized, a dense layer of chromium oxide is formed on the surface of stainless steel, called a passivation layer. The passivation layer is (3-5)10-6mm thick to prevent the metal from continuing to oxidize and prevent oxygen and iron from oxidizing to form loose iron oxide like carbon steel after oxidation. The loose iron oxide of carbon steel is oxidized, rusted and continuously peeled off. However, due to the presence of chromium in stainless steel, a dense chromium passivation layer is produced to protect the metal from continuous oxidation. The stainless steel passivation film has an automatic recovery function after damage, so the chromium content isStainless steelbright light tubeThe key to corrosion resistance. Copper and aluminum also have a dense passivation layer, but the strength of copper and aluminum is lower than that of stainless steel.

Solution is the key to improve the corrosion resistance and toughness of stainless steel bright tube

MostStainless steelbright light tubeIt is made of austenitic stainless steel with a nickel content of more than 8%, and the ferrite content in austenitic stainless steel generally does not exceed 8%. At high temperatures, carbon steel, alloy steel, and stainless steel are all austenitic, face-centered cubic lattices, with three carbon atoms in one cube. If it is carbon steel and low alloy steel, it will be in austenite, after cooling, the distance between iron atoms will be reduced, austenite will shrink, it will be transformed into a ferrite lattice with only one carbon atom, so it is easy to precipitate carbides from austenitic austenitic stainless steel containing more than 8% nickel, the atomic weight of nickel is 58.71, greater than the 55.847 of iron. In austenite, the crystal lattice of austenite is expanded after the iron atoms are replaced by nickel atoms. When the solution is heated and then rapidly cooled by water spray, the crystal lattice shrinks rapidly, and the carbon is too late to precipitate, so the carbon atoms are fixed in the austenite, the crystal lattice, which is called the solution.

If austenitic stainless steel is rapidly heated and cooled, carbon atoms will be dissolved in the crystal lattice, austenite, and carbides will not precipitate at the grain boundary, thereby avoiding the formation of chromium carbide, avoiding chromium loss at the grain boundary, and avoiding the compound oxidation of oxygen and iron, thereby avoiding intergranular corrosion. Similarly, austenitic stainless steel is cooled quickly, carbon atoms are dissolved in austenite, the crystal lattice, there is no carbide on the grain boundary, and there is no obstacle when the metal is deformed, so the stainless steel becomes very soft, with large elongation and good Toughness; however, when the carbon steel with a ferrite matrix is rapidly quenched and cooled, carbides precipitate and toughness decreases; the faster the cooling, the coarser the carbides precipitated and the lower the toughness. Therefore, the solid solution of austenitic stainless steel must be heated and rapidly cooled to avoid carbide precipitation.

3 Duplex Stainless Steelbright light tubeResistance to chloride ion corrosion

The passive film of the stainless steel surface is fragile in these places due to defects, impurities and solute inhomogeneities in the steel. When the etching pit exceeds a critical size (several tens of microns), it is easily destroyed in a chlorine-containing etching solution, and the destroyed part becomes an activated anode, surrounded by a cathode region. When the anode area is very small, the current density of the anode is very high and the active dissolution is accelerated, resulting in many needle-like pores and "pitting". Due to its small radius and strong penetration, chloride ions are easy to enter the passivation film and adsorb on the metal surface, and then form strong acid and weak alkali salts with Fe2 ions produced by corrosion, making the microenvironment more acidic and accelerating the corrosion process. Duplex stainless steel contains half austenite and half ferrite. Black is ferrite and white is austenite. There are two phases in duplex stainless steel, which are distributed in layers. The presence of one phase prevents the development of cracks in the other phase. Cracks propagate in the ferrite phase and need to bypass the island-like austenite phase that acts as a barrier. Therefore, duplex stainless steelbright light tubeResistant to chloride ion corrosion.