904L steel: An outstanding material for withstanding harsh corrosive environments
904L (UNS N08904, EN 1.4539) belongs to super austenitic stainless steel. It is a low-carbon, high-nickel and high-molybdenum austenitic stainless and acid-resistant steel, which was initially developed by the French H · S company. This steel grade is specially designed for harsh corrosive environments and performs exceptionally well in various complex working conditions.
Its characteristics are extremely remarkable. Firstly, its corrosion resistance is first-class. It has excellent corrosion resistance in non-oxidizing acids such as sulfuric acid, acetic acid, formic acid, and phosphoric acid. It can adapt to various concentrations of sulfuric acid below 70℃, and under normal pressure, it has good resistance to any concentration and temperature of acetic acid and mixed acids of formic acid and acetic acid. In neutral chloride-containing media, it has excellent resistance to pitting corrosion, crevice corrosion and stress corrosion. Secondly, 904L has excellent processing performance, with superior machinability and weldability, making it convenient to manufacture components of various complex shapes. In addition, it has a fully austenitic structure. Compared with common high-molybdenum austenitic stainless steels, it is less sensitive to the precipitation of ferrite and α phase, and its performance is more stable.
In terms of chemical composition, the carbon content of 904L is extremely low, not exceeding 0.020% at most, effectively avoiding the risk of intergranular corrosion after general heat treatment and welding. The chromium content is between 19.0 and 23.0%, and the nickel content is between 23.0 and 28.0%. The high chromium and nickel content enables it to resist corrosion in various oxidizing and reducing environments. The molybdenum content is 4.0-5.0%, and the copper content is 1.0-2.0%. The synergistic effect of molybdenum and copper enhances the steel's resistance to pitting and crevice corrosion in reducing acids. Meanwhile, the content of elements such as manganese and silicon is also reasonably controlled, and the content of impurity elements such as phosphorus and sulfur is extremely low, ensuring the high quality of the steel.
The 904L has a wide range of applications. In the field of petroleum and petrochemical equipment, it is often used to manufacture key components such as reactors; In terms of equipment for the storage and transportation of sulfuric acid, such as heat exchangers, with their excellent resistance to sulfuric acid corrosion, they ensure the long-term stable operation of the equipment. In the flue gas desulfurization equipment of power plants, 904L is often used in the main parts such as the tower body and flue of the absorption tower to resist complex corrosive environments. In the scrubbers and fans of organic acid treatment systems, as well as in fields with high requirements for material corrosion resistance such as seawater treatment devices, papermaking industry equipment, food equipment, and pharmaceutical equipment, 904L has also played a significant role and become an ideal material for dealing with harsh corrosive environments.